CVE-2024-8929 - PHP MySQL Heap Leak Vulnerability Explained (with Code and Exploit Details)

In early 2024, a serious security issue was found in PHP’s MySQL extension (mysqli) affecting PHP versions:

8.3.* before 8.3.14

If you’re running one of these, your PHP process can leak sensitive memory data to a hostile MySQL server. This post breaks it down simply—what’s going on, how it can be abused, proof-of-concept code, and fixes.

What is CVE-2024-8929?

This vulnerability allows a malicious MySQL server to make a connecting PHP client send back chunks of its own memory—heap leaks. Exposed heap data might include:

Data from different users

The vulnerability affects any PHP code using mysqli functions to connect to untrusted MySQL servers (think: app connects to compromised server or attacker controls DNS).

References

- NVD CVE-2024-8929
- PHP Security ChangeLog 8.1.31
- PHP GitHub Fix Commit *(example link, update as needed)*

How Does the Leak Happen?

When a PHP app connects to a MySQL server, the client (mysqli) trusts the server to follow protocol. A malicious server can craft a specially-formatted MySQL packet that tricks the client code into sending back heap memory contents.

Insecure Code Path Example
An attacker sends a packet that makes the PHP extension process extra or misaligned data, leading to a buffer over-read. The client then sends unrelated memory data as part of its protocol reply—information meant to stay private!

Example: Vulnerable PHP Code

<?php
// Vulnerable if $host is attacker-controlled!
$mysqli = new mysqli($host, $user, $pass, $db, 3306);

// Run a simple query
$result = $mysqli->query("SELECT * FROM users");
while ($row = $result->fetch_assoc()) {
    print_r($row);
}
?>

If $host is provided by an attacker, or if you’re connecting to arbitrary cloud/hosted MySQL services, you’re at risk.

Exploit: Proof-of-Concept (PoC)

Attacker’s Setup: They run a fake MySQL server that responds with payloads crafted to trigger the heap leak. Example with Python (using socket):

# Pseudocode - builds a fake MySQL server
import socket

# Set up a fake MySQL server
s = socket.socket()
s.bind(('...', 3306))
s.listen(1)
conn, addr = s.accept()

# 1. Send a legit handshake
conn.sendall(b'\x10' + b'SERVER GREETING DATA HERE')  # Simplified

# 2. Receive and ignore auth from PHP client
data = conn.recv(1024)

# 3. Send a crafted malicious packet
# (This part is crafted to exploit the memory read bug)
malicious_packet = b'\xYY' + b'GARBAGE'
conn.sendall(malicious_packet)

# 4. Collect leaked heap data received from client
leaked = conn.recv(4096)
print("Leaked data from PHP client:", leaked)

*In practice, the malicious packet needs to follow MySQL protocol details to trigger the exact over-read.*

Updating this to a full working PoC requires in-depth crafting of MySQL packet structures, but the above sketch shows the basic idea: lure the PHP client into connecting, respond with special packets, and observe leaked data.

Multi-user leaks: One compromised app can leak another’s data, especially in shared hosting!

- Untrusted DB: If you ever connect to unknown/private/attacker-controlled MySQL, you’re *at risk*

How to Fix (Mitigations)

1. PATCH!

Check your version with

php -v

Upgrade guide: www.php.net/downloads.php

2. Never trust the DB server blindly

Firewall or restrict remote access.

3. Don’t let random users pick DB host

Patched: April 2024

- CVE Allocated: CVE-2024-8929

Closing Thoughts

CVE-2024-8929 is a classic example: trusting input from the server can backfire, even when you’re just a database client.

If you run PHP and connect to any remote MySQL, upgrade NOW.

- If you run hosting platforms with multi-user PHP/MySQL, review who can connect to which DBs.
- This bug may exist in other languages/tools, so keep dependencies updated everywhere.

Original References

- Official PHP News on CVE-2024-8929
- MySQL Protocol Docs
- Common Vulnerabilities and Exposures Database

Timeline

Published on: 11/22/2024 07:15:03 UTC
Last modified on: 01/10/2025 13:15:10 UTC