Medium Severity
Published: Nov 2, 2026
# php2shell — PHP 8.4.26 session vulnerability reproduction
[中文](#中文) | [English](#english)
---
## English
Under the constraints of "completely remote, HTTP only, target page has no `session_start()`, no PHP code written on target side", use **a single `exploit.py`** to achieve RCE on PHP 8.4.26 + Apache prefork + mod_php. The 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 in the [docker/](docker/) directory of this repository.
This is not a generic ASLR bypass, nor is ASLR disabled:
- The exploitation process leaks only **Zend MM chunk base** and **libphp base** through two out-of-bounds reads, without leaking libc, stack, or complete memory maps.
- The address space is still randomized by ASLR. Host kernel ASLR (kASLR), container runtime, kernel `mmap` behavior, allocator, and specific builds of PHP/Apache all affect heap layout and leak results.
- Heap geometry, calibration values, and libphp offsets in the chain are empirically measured against the official image and do not include address scanning or brute-force enumeration. After changing images, PHP builds, or distributions, even if addresses can still be leaked, the subsequent forged object layout 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`ing it, so libphp mappings and address space dependencies at each stage are preserved.
- `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 is still in effect; retrying only switches to a different worker and does not "defeat" ASLR.
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-click 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 mounted configurations 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 the 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 to be ready 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 exploitation with one command; first run automatically reads libphp offsets
python3 exploit.py -u http://127.0.0.1:8088