CVE-2024-5629: MongoDB PyMongo Out-of-Bounds Vulnerability

CVE-2024-5629 Overview

An out-of-bounds read vulnerability exists in the bson module of PyMongo versions 4.6.2 and earlier. This flaw allows deserialization of malformed BSON data provided by a server to raise an exception that may contain arbitrary application memory. The vulnerability (CWE-125) could enable attackers to extract sensitive information from application memory through carefully crafted BSON responses.

Critical Impact

This out-of-bounds read vulnerability can expose sensitive application memory contents when processing malformed BSON data from a malicious MongoDB server, potentially leading to information disclosure and application crashes.

Affected Products

• MongoDB PyMongo versions up to and including 4.6.2
• Debian Linux 10.0 (with affected PyMongo packages)

Discovery Timeline

• June 5, 2024 - CVE-2024-5629 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2024-5629

Vulnerability Analysis

The vulnerability resides in PyMongo's BSON deserialization logic within the bson module. When processing BSON (Binary JSON) data received from a MongoDB server, the library fails to properly validate buffer boundaries. An attacker controlling or impersonating a MongoDB server can craft malformed BSON documents that trigger out-of-bounds memory reads during deserialization.

The improper boundary checking means that when the parser encounters specially crafted BSON data with invalid length fields or malformed structures, it attempts to read beyond allocated memory buffers. This memory content is then exposed through exception messages that bubble up to the application layer.

Root Cause

The root cause is insufficient bounds checking in the BSON deserialization routines within PyMongo. The bson module does not adequately validate the length and structure fields embedded in BSON documents before attempting to read data. When malformed BSON with inconsistent or excessive length indicators is processed, the parser reads beyond the actual data buffer boundaries, accessing adjacent memory regions that may contain sensitive application data.

Attack Vector

The attack vector is network-based and requires user interaction. An attacker must position themselves as a MongoDB server or compromise an existing MongoDB server that the target PyMongo client connects to. The attack flow is as follows:

1. The attacker establishes a malicious MongoDB server or performs a man-in-the-middle attack
2. When the PyMongo client issues queries, the attacker responds with crafted BSON documents containing malformed length fields
3. PyMongo's bson module attempts to deserialize the malformed data
4. The deserialization process reads beyond buffer boundaries due to improper validation
5. An exception is raised containing the out-of-bounds memory content
6. If the exception is logged or displayed, the leaked memory becomes accessible to the attacker

The vulnerability mechanism involves the BSON parser trusting length fields within the binary format without proper boundary validation. When a BSON document specifies a string or binary data length that exceeds the actual buffer size, the parser continues reading into adjacent memory. For detailed technical information, refer to MongoDB Python Issue PYTHON-4305.

Detection Methods for CVE-2024-5629

Indicators of Compromise

• Unexpected exceptions or error messages containing binary data or memory artifacts during MongoDB operations
• Anomalous BSON parsing errors in application logs, particularly with unusual byte sequences in error messages
• MongoDB connection attempts to unknown or untrusted server addresses
• Application crashes during BSON deserialization with memory-related errors

Detection Strategies

• Implement application-level monitoring for BSON deserialization exceptions that contain unusual data patterns
• Deploy network monitoring to detect connections to unverified MongoDB servers or potential MITM attacks on MongoDB traffic
• Conduct software composition analysis (SCA) to identify PyMongo versions 4.6.2 and earlier in your environment
• Monitor for applications exhibiting unexpected memory disclosure behaviors during database operations

Monitoring Recommendations

• Enable verbose logging for PyMongo operations and monitor for deserialization-related exceptions
• Implement TLS/SSL certificate pinning for MongoDB connections to prevent server impersonation
• Deploy runtime application self-protection (RASP) solutions capable of detecting memory access violations
• Establish baseline network traffic patterns for MongoDB connections to identify anomalies

How to Mitigate CVE-2024-5629

Immediate Actions Required

• Upgrade PyMongo to version 4.6.3 or later, which contains the fix for this vulnerability
• Audit all applications and services using PyMongo to identify affected deployments
• Ensure MongoDB connections use TLS/SSL with proper certificate validation to prevent server impersonation
• Implement network segmentation to restrict MongoDB server connectivity to trusted endpoints only

Patch Information

MongoDB has addressed this vulnerability and released updated versions of PyMongo. The fix is tracked in MongoDB Python Issue PYTHON-4305. Debian has also released security updates as documented in the Debian LTS Announce June 2024 and Debian LTS Announce September 2024 advisories.

Organizations should update PyMongo packages through their package managers and verify the installed version is 4.6.3 or higher.

Workarounds

• If immediate patching is not possible, implement strict network controls to ensure PyMongo only connects to known, trusted MongoDB servers
• Enable TLS/SSL for all MongoDB connections and implement certificate validation to prevent man-in-the-middle attacks
• Configure application exception handling to sanitize error messages before logging or displaying, preventing potential memory disclosure
• Consider implementing a network-level proxy that validates BSON responses before passing them to the application

# Configuration example
# Upgrade PyMongo to patched version
pip install --upgrade pymongo>=4.6.3

# Verify installed version
pip show pymongo | grep Version

# For Debian systems, update via apt
sudo apt update && sudo apt upgrade python3-pymongo