Medium Severity
Published: Nov 2, 2026
# php2shell — PHP 8.4.26 Session Vulnerability Reproduction
[Chinese](#chinese) | [English](#english)
---
## English
Under the constraints of "fully remote, HTTP only, target page without `session_start()`, no PHP written on the 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 [docker/](docker/) of this repository.
This is not a generic ASLR bypass, nor does it disable ASLR:
- 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 mapping.
- The address space remains 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.
- The heap geometry, calibration values, and libphp offsets in the chain are empirically measured for 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 object forgery layout may not hold.
There are also hard prerequisites 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`, preserving libphp mapping and 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 `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 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-Command Reproduction
This repository does not compile PHP/Apache, nor does it have `docker build`: the environment is the official `php:8.4.26-apache` image plus configuration mounts from `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 the entire exploitation with one command; first run automatically reads libphp offset
python3 exploit.py -u http://127.0.0.1:8088
```