Medium Severity
Published: Nov 6, 2026
# php2shell — PHP 8.4.26 Session Vulnerability Reproduction
[中文](#中文) | [English](#english)
---
## English
Under the constraints of "fully remote, HTTP-only, target page without `session_start()`, no PHP code written to target", use **a single `exploit.py`** to achieve RCE on PHP 8.4.26 + Apache prefork + mod_php. Target page contains only `<?php echo "OK\n"; ?>`.
### Supported Scope (Read First)
> **The only supported runtime environment is the official `php:8.4.26-apache` image** (PHP 8.4.26 / Debian 12 / Apache prefork + mod_php) combined with the configuration under [docker/](docker/) in this repository.
This is not a generic ASLR bypass, nor is ASLR disabled:
- The exploitation process leaks only the **Zend MM chunk base** and **libphp base** via two out-of-bounds reads, without leaking libc, stack, or complete memory mappings.
- Address space remains randomized by ASLR. Host kernel ASLR (kASLR), container runtime, kernel `mmap` behavior, allocator, and the specific builds of PHP/Apache all affect heap layout and leak results.
- Heap geometry, calibration values, and libphp offsets in the chain are measured against the official image and do not include address scanning or brute-force enumeration. After switching images, PHP builds, or distributions, even if addresses can still be leaked, the subsequent layout of forged objects may not hold.
There are also hard requirements on the Apache side:
- Must be **prefork MPM + single worker + mod_php**. After a child process aborts, the parent process directly `fork`s a new worker without `exec`, thus preserving libphp mappings and the address space dependencies for each stage.
- `docker/apache.conf` fixes `StartServers/MinSpareServers/MaxSpareServers/MaxRequestWorkers/ServerLimit = 1`, `MaxConnectionsPerChild = 0`, and disables KeepAlive.
- Multiple workers, event/worker MPM, Apache restart/graceful restart, worker re-`exec`, container rebuild, or parent process exit may re-randomize addresses or route requests to different processes, breaking the entire chain.
- If any stage of leaking fails, ASLR remains effective; retry simply switches to a different worker and does not "defeat" ASLR.
The current RCE also requires: `display_errors=1`, `memory_limit=8M`, `max_input_vars=1000`, `session.use_cookies=1`, `session.use_strict_mode=0`, `session.upload_progress.enabled=1`.
### One-Command Reproduction
This repository does not compile PHP/Apache and has no `docker build`: the environment is the official `php:8.4.26-apache` image plus configuration mounts under `docker/`.
```bash
# Dependencies: Docker Engine/Desktop + Docker Compose v2 + Python 3.9+
git clone https://github.com/9bie/php2shell-bypass-aslr-exp.git
cd php2shell-bypass-aslr-exp
# 1) Pull official image (PHP 8.4.26 / Debian 12 / Apache prefork)
docker compose -f docker/docker-compose.yml pull
# 2) Start target: single worker, display_errors=On, memory_limit=8M
docker compose -f docker/docker-compose.yml up -d
# 3) Wait for Apache readiness and confirm normal page
for i in $(seq 1 20); do
curl -fsS http://127.0.0.1:8088/index.php >/dev/null 2>&1 && break
sleep 0.5
done
curl -s http://127.0.0.1:8088/index.php # OK
# 4) Complete the entire exploitation with one command; first run automatically reads libphp offset
python3 exploit.py -u http://127.0.0.1:8088
```