CVE-2021-4043: Gpac NULL Pointer Dereference Flaw

CVE-2021-4043 Overview

CVE-2021-4043 is a NULL Pointer Dereference vulnerability affecting the GPAC multimedia framework. GPAC is an open-source multimedia framework used for creating, packaging, and streaming multimedia content in various formats. The vulnerability exists in versions prior to 1.1.0 and can be exploited when a user opens a specially crafted media file, leading to application crashes and denial of service conditions.

Critical Impact

This vulnerability allows attackers to cause application crashes through NULL pointer dereference, resulting in denial of service when users process malicious media files with GPAC.

Affected Products

• GPAC versions prior to 1.1.0
• Debian Linux 11.0 (through packaged GPAC)

Discovery Timeline

• 2022-02-04 - CVE-2021-4043 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-4043

Vulnerability Analysis

The vulnerability stems from improper handling of pointer references within the GPAC codebase. When processing certain media files or streams, the application fails to validate pointer values before dereferencing them. This missing validation allows an attacker to trigger a code path where a NULL pointer is dereferenced, causing the application to crash immediately.

The local attack vector requires user interaction, meaning a victim must be convinced to open a maliciously crafted file. While this limits the attack surface compared to network-exploitable vulnerabilities, it remains a significant concern in environments where GPAC is used to process untrusted media content. The vulnerability affects only availability (denial of service) without compromising data confidentiality or integrity.

Root Cause

The root cause is a classic NULL Pointer Dereference (CWE-476) defect where the code attempts to access memory through a pointer that has not been properly initialized or validated. In this case, certain execution paths within GPAC fail to check whether a pointer is NULL before dereferencing it, leading to immediate process termination when the pointer value is zero.

Attack Vector

Exploitation requires local access and user interaction. An attacker would need to craft a malicious media file that triggers the vulnerable code path when processed by GPAC. The attack scenario typically involves:

1. Creating a specially crafted media file that exploits the NULL pointer condition
2. Distributing the file to potential victims through social engineering, malicious websites, or email attachments
3. The victim opens the file using GPAC or an application that uses GPAC libraries
4. The vulnerable code path is triggered, causing application crash

The vulnerability does not provide arbitrary code execution capabilities but effectively denies service to users attempting to process legitimate media content after encountering the malicious file.

Detection Methods for CVE-2021-4043

Indicators of Compromise

• Unexpected GPAC application crashes when opening media files
• Process termination signals (SIGSEGV) in system logs related to GPAC processes
• Crash dump files indicating NULL pointer access in GPAC libraries
• Repeated application failures when processing files from untrusted sources

Detection Strategies

• Monitor application crash logs for GPAC-related segmentation faults
• Implement file integrity monitoring to detect potentially malicious media files
• Deploy endpoint detection solutions that can identify crash patterns indicative of exploitation attempts
• Review system logs for repeated GPAC process terminations

Monitoring Recommendations

• Enable crash reporting for GPAC applications to capture NULL pointer dereference events
• Monitor for unusual patterns of application restarts or failures
• Implement security monitoring for media file processing pipelines
• Track GPAC version deployments to identify vulnerable instances

How to Mitigate CVE-2021-4043

Immediate Actions Required

• Update GPAC to version 1.1.0 or later immediately
• Review and update Debian Linux 11.0 systems with the latest security patches
• Restrict processing of media files from untrusted sources until patches are applied
• Implement input validation for media files before processing

Patch Information

The vulnerability has been addressed by the GPAC development team in commit 64a2e1b799352ac7d7aad1989bc06e7b0f2b01db. Users should upgrade to GPAC version 1.1.0 or later to receive the fix. Debian users should apply the security updates referenced in DSA-5411.

Additional resources:

• GitHub Commit Update
• Huntr Bounty Report

Workarounds

• Avoid processing media files from untrusted or unknown sources until patches can be applied
• Implement sandboxing for GPAC applications to contain potential crashes
• Use application-level crash recovery mechanisms to minimize service disruption
• Consider temporarily disabling automated media processing workflows that use vulnerable GPAC versions

# Update GPAC on Debian-based systems
sudo apt update
sudo apt install --only-upgrade gpac

# Verify installed version (should be 1.1.0 or later)
gpac -version