CVE-2026-4015: GPAC Buffer Overflow Vulnerability

CVE-2026-4015 Overview

A stack-based buffer overflow vulnerability has been identified in GPAC version 26.03-DEV, affecting the txtin_process_texml function within the TeXML File Parser component. The flaw exists in the file src/filters/load_text.c and can be triggered by processing a maliciously crafted TeXML file, leading to memory corruption and potential code execution.

Critical Impact

This vulnerability allows local attackers with limited privileges to exploit a stack-based buffer overflow in GPAC's TeXML parsing functionality, potentially enabling arbitrary code execution or denial of service.

Affected Products

• GPAC 26.03-DEV
• GPAC versions prior to commit d29f6f1ada5cc284cdfa783b6f532c7d8bd049a5

Discovery Timeline

• 2026-03-12 - CVE-2026-4015 published to NVD
• 2026-03-12 - Last updated in NVD database

Technical Details for CVE-2026-4015

Vulnerability Analysis

The vulnerability resides in the txtin_process_texml function within GPAC's TeXML File Parser (src/filters/load_text.c). When parsing specially crafted TeXML input, the function fails to properly validate buffer boundaries before writing data to a stack-allocated buffer. This improper restriction of operations within the bounds of a memory buffer (CWE-119) allows an attacker to overflow the stack buffer and potentially corrupt adjacent memory regions, including return addresses and saved registers.

TeXML is a file format used for multimedia text content, and GPAC's parser processes these files to extract and render textual overlays for multimedia applications. The lack of proper bounds checking during the parsing routine creates an exploitable condition that could lead to denial of service through application crash, or in certain scenarios, arbitrary code execution if an attacker can control the overflowed data.

Root Cause

The root cause of this vulnerability is improper input validation within the txtin_process_texml function. The code fails to verify that input data from TeXML files does not exceed the size of the stack-allocated buffer before copying it. This allows specially crafted input to write beyond the buffer's allocated space on the stack, leading to memory corruption classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Attack Vector

This vulnerability requires local access to the system where GPAC is installed. An attacker must craft a malicious TeXML file and convince a user to process it using GPAC, or place the malicious file in a location where it will be automatically processed. The attack requires low privileges and no user interaction beyond opening or processing the malicious file.

The exploitation mechanism involves creating a TeXML file with oversized data fields that exceed the expected buffer size in the txtin_process_texml function. When GPAC parses this file, the overflow occurs on the stack, potentially allowing the attacker to overwrite control flow data. A proof-of-concept script demonstrating this vulnerability has been made available publicly. For technical details, see the GitHub Issue #3467 and the associated PoC file.

Detection Methods for CVE-2026-4015

Indicators of Compromise

• GPAC processes crashing unexpectedly when handling TeXML files
• Stack smashing detected errors or segmentation faults in GPAC logs
• Suspicious TeXML files with abnormally large text fields or malformed structure
• Memory corruption artifacts in crash dumps associated with the txtin_process_texml function

Detection Strategies

• Monitor GPAC process behavior for abnormal crashes or termination patterns when processing TeXML content
• Implement file integrity checks on TeXML files before processing to detect oversized or malformed input
• Deploy endpoint detection rules to identify crash signatures associated with stack buffer overflows in media processing applications
• Use application sandboxing to limit the impact of potential exploitation

Monitoring Recommendations

• Enable verbose logging for GPAC operations to capture detailed error information
• Monitor system logs for stack overflow or buffer overflow indicators related to multimedia processing
• Track file access patterns for TeXML files from untrusted sources
• Implement SentinelOne Singularity Platform for real-time detection of memory corruption exploitation attempts

How to Mitigate CVE-2026-4015

Immediate Actions Required

• Update GPAC to a version that includes commit d29f6f1ada5cc284cdfa783b6f532c7d8bd049a5 or later
• Avoid processing TeXML files from untrusted or unknown sources until patched
• Implement application sandboxing for GPAC processes to limit potential exploit impact
• Review recent TeXML processing activities for signs of exploitation

Patch Information

The GPAC development team has addressed this vulnerability in commit d29f6f1ada5cc284cdfa783b6f532c7d8bd049a5. Users should update their GPAC installation to include this fix. The patch implements proper bounds checking in the txtin_process_texml function to prevent stack buffer overflow conditions.

For additional context, refer to the GPAC GitHub Repository and GitHub Issue #3467.

Workarounds

• Disable TeXML file processing if not required for your use case
• Implement input validation on TeXML files before passing them to GPAC
• Run GPAC in a sandboxed environment with restricted privileges
• Use file type filtering to block potentially malicious TeXML files from untrusted sources

# Configuration example - Run GPAC with reduced privileges in a restricted environment
# Create a dedicated user for GPAC processing
sudo useradd -r -s /bin/false gpac-service

# Run GPAC with limited capabilities (example using firejail)
firejail --private --noroot gpac -i input.mp4 -o output.mp4