CVE-2026-3949: libheif Buffer Overflow Vulnerability

CVE-2026-3949 Overview

An out-of-bounds read vulnerability has been identified in strukturag libheif versions up to and including 1.21.2. This memory corruption vulnerability affects the vvdec_push_data2 function within the file libheif/plugins/decoder_vvdec.cc, which is part of the HEIF File Parser component. By manipulating the size argument, an attacker with local access can trigger an out-of-bounds read condition, potentially leading to information disclosure or application crashes.

Critical Impact

Local attackers can exploit this vulnerability to read memory beyond allocated boundaries in the HEIF file parsing process, potentially exposing sensitive information or causing denial of service conditions.

Affected Products

• strukturag libheif versions up to 1.21.2
• Applications utilizing the libheif HEIF File Parser with vvdec decoder plugin
• Systems processing HEIF/HEIC image files through vulnerable libheif versions

Discovery Timeline

• 2026-03-11 - CVE-2026-3949 published to NVD
• 2026-03-12 - Last updated in NVD database

Technical Details for CVE-2026-3949

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw exists in the vvdec decoder plugin component of libheif, specifically within the vvdec_push_data2 function located in libheif/plugins/decoder_vvdec.cc. When processing HEIF files, the function fails to properly validate the size argument, allowing attackers to craft malicious input that triggers memory reads beyond the allocated buffer boundaries.

The exploit has been publicly disclosed, and proof-of-concept materials are available. The vulnerability requires local access to exploit, meaning an attacker would need to convince a user to open a specially crafted HEIF file or have local access to a system processing such files.

Root Cause

The root cause stems from insufficient bounds checking when handling the size parameter in the vvdec_push_data2 function. The code path allows processing of data without adequate validation that the specified size falls within the boundaries of the allocated memory buffer. This improper memory buffer operation restriction enables attackers to specify a size value that causes the function to read beyond the legitimate data boundaries.

Attack Vector

The attack requires local access and involves crafting a malicious HEIF file with manipulated size values. When a vulnerable application processes this file using libheif with the vvdec decoder plugin, the malformed size argument triggers the out-of-bounds read condition. An attacker could potentially:

1. Craft a specially malformed HEIF/HEIC image file
2. Deliver the malicious file to a target system
3. Trigger processing of the file through any application using vulnerable libheif versions
4. Exploit the out-of-bounds read to leak sensitive memory contents or cause application instability

The vulnerability mechanism involves improper handling of the size argument in the vvdec decoder plugin. When parsing HEIF files, the vvdec_push_data2 function accepts a size parameter that should define the boundaries of data to process. Due to insufficient validation, attackers can specify size values that exceed the actual buffer allocation, causing the function to read beyond legitimate memory boundaries. For technical details, see the GitHub Issue #1712 and the PoC repository.

Detection Methods for CVE-2026-3949

Indicators of Compromise

• Unexpected application crashes when processing HEIF/HEIC image files
• Memory access violations or segmentation faults in applications using libheif
• Abnormal memory consumption patterns during image file processing
• Error logs indicating buffer overread conditions in vvdec decoder operations

Detection Strategies

• Monitor for crashes or exceptions in applications utilizing libheif for HEIF file processing
• Implement file integrity monitoring for unexpected HEIF files in sensitive directories
• Deploy memory protection tools to detect out-of-bounds memory access attempts
• Audit system logs for vvdec decoder plugin errors or anomalies

Monitoring Recommendations

• Enable AddressSanitizer (ASan) in development and testing environments to detect out-of-bounds reads
• Configure application crash reporting to capture and analyze HEIF-related failures
• Monitor for unusual patterns in image file processing across endpoint systems
• Implement file scanning for malformed HEIF files before processing

How to Mitigate CVE-2026-3949

Immediate Actions Required

• Update libheif to a patched version containing commit b97c8b5f198b27f375127cd597a35f2113544d03
• Audit all applications and systems using libheif for HEIF file processing
• Implement input validation for HEIF files before processing with libheif
• Consider temporarily disabling the vvdec decoder plugin if not required for operations

Patch Information

The strukturag development team has addressed this vulnerability through commit b97c8b5f198b27f375127cd597a35f2113544d03. Organizations should apply this patch immediately or upgrade to a libheif version that includes this fix. The patch adds proper bounds checking for the size argument in the vvdec_push_data2 function to prevent out-of-bounds read conditions.

Additional technical details and discussion can be found in GitHub Issue #1712 and the VulDB entry #350381.

Workarounds

• Disable or remove the vvdec decoder plugin from libheif configurations where VVC decoding is not required
• Implement strict file type validation and sanitization for all incoming HEIF/HEIC files
• Use application sandboxing to limit the impact of potential exploitation
• Deploy endpoint protection solutions capable of detecting memory corruption attempts

# Verify libheif version and check for vulnerable installations
# Check installed libheif version
pkg-config --modversion libheif

# If using git, verify the patch is applied
cd /path/to/libheif
git log --oneline | grep b97c8b5

# Rebuild libheif with the security patch
git pull origin main
mkdir build && cd build
cmake ..
make && sudo make install