CVE-2022-31626: PHP pdo_mysql Buffer Overflow RCE Flaw

CVE-2022-31626 Overview

CVE-2022-31626 is a buffer overflow vulnerability affecting PHP versions 7.4.x below 7.4.30, 8.0.x below 8.0.20, and 8.1.x below 8.1.7. The vulnerability exists within the pdo_mysql extension when using the mysqlnd driver. When a third party is allowed to supply the host to connect to and the password for the connection, an excessively long password can trigger a buffer overflow in PHP, potentially leading to remote code execution.

Critical Impact

This buffer overflow vulnerability in PHP's pdo_mysql extension can be exploited by attackers to achieve remote code execution on affected systems, potentially leading to complete system compromise.

Affected Products

• PHP 7.4.x versions below 7.4.30
• PHP 8.0.x versions below 8.0.20
• PHP 8.1.x versions below 8.1.7
• Debian Linux 10.0
• Debian Linux 11.0

Discovery Timeline

• 2022-06-16 - CVE-2022-31626 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-31626

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), commonly known as a classic buffer overflow. The flaw resides in how PHP's pdo_mysql extension with the mysqlnd driver handles password authentication during database connection establishment.

When an application allows user-controlled input for database connection parameters, particularly the password field, attackers can supply a password of excessive length. The mysqlnd driver fails to properly validate the length of the password before copying it into a fixed-size buffer, resulting in a buffer overflow condition.

The attack requires network access and low privileges, but no user interaction is needed. Successful exploitation can lead to complete compromise of confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of CVE-2022-31626 is insufficient bounds checking in the mysqlnd driver's password handling routine within the pdo_mysql extension. The driver allocates a fixed-size buffer for password storage but does not verify that the incoming password length fits within this buffer before performing the copy operation. This classic buffer overflow pattern allows an attacker to overwrite adjacent memory regions.

Attack Vector

The attack vector for this vulnerability requires specific conditions to be met:

1. The target application must use PHP's pdo_mysql extension with the mysqlnd driver
2. The application must allow third-party input to control the database host and password parameters
3. The attacker submits an excessively long password string during connection establishment

When these conditions are met, the attacker-supplied oversized password overwrites memory beyond the allocated buffer. Depending on the memory layout and exploitation technique, this can lead to arbitrary code execution, allowing the attacker to run malicious code with the privileges of the PHP process.

The vulnerability is exploited over the network, making it particularly dangerous for web applications that accept user input for database connection parameters, such as multi-tenant applications or database administration tools.

Detection Methods for CVE-2022-31626

Indicators of Compromise

• Abnormally long password strings in MySQL/MariaDB connection attempts exceeding typical password lengths
• PHP process crashes or unexpected terminations, particularly during database connection operations
• Unusual memory access patterns or segmentation faults in PHP error logs
• Signs of code execution following pdo_mysql connection attempts

Detection Strategies

• Monitor PHP error logs for buffer overflow indicators, memory corruption, or segmentation faults related to pdo_mysql operations
• Implement input validation rules to flag excessively long password strings in database connection parameters
• Deploy runtime application self-protection (RASP) solutions to detect memory corruption attempts
• Use SentinelOne's behavioral AI to identify anomalous process behavior indicative of exploitation

Monitoring Recommendations

• Enable comprehensive logging for PHP applications, capturing connection parameters (excluding actual passwords)
• Monitor for unusual PHP process behavior, including unexpected child processes or network connections
• Track PHP version inventory across your environment to identify unpatched instances
• Configure alerts for MySQL/MariaDB authentication failures with unusually large connection payloads

How to Mitigate CVE-2022-31626

Immediate Actions Required

• Upgrade PHP to version 7.4.30, 8.0.20, or 8.1.7 or later depending on your PHP branch
• Audit applications to identify any that allow user-controlled database connection parameters
• Implement strict input validation on any user-supplied database connection strings, particularly password length limits
• Consider using a Web Application Firewall (WAF) to filter excessively long password inputs

Patch Information

PHP has released security patches addressing this vulnerability. Organizations should upgrade to the following versions or later:

• PHP 7.4.x: Upgrade to 7.4.30 or later
• PHP 8.0.x: Upgrade to 8.0.20 or later
• PHP 8.1.x: Upgrade to 8.1.7 or later

For detailed information, refer to PHP Bug Report #81719. Distribution-specific patches are also available via Debian Security Advisory DSA-5179, Gentoo GLSA 202209-20, and respective Fedora package announcements.

Workarounds

• Restrict user input for database connection parameters; never allow untrusted input to control host or password values
• Implement application-level password length validation before passing to PDO connection functions
• Use connection pooling or centralized database connection management to reduce exposure
• Consider switching to mysqli with a different driver if pdo_mysql with mysqlnd cannot be immediately patched

# Verify your PHP version and check for vulnerable installations
php -v

# Check for pdo_mysql extension with mysqlnd driver
php -i | grep -i "pdo_mysql\|mysqlnd"

# Update PHP on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade php

# Update PHP on RHEL/CentOS/Fedora systems
sudo dnf update php