CVE-2023-46407: FFmpeg Buffer Overflow Vulnerability

CVE-2023-46407 Overview

CVE-2023-46407 is an Out-of-Bounds Read vulnerability discovered in FFmpeg, the widely-used open-source multimedia framework. The vulnerability exists in the read_vlc_prefix() function within the JPEG XL parser component (libavcodec/jpegxl_parser.c), where improper handling of the dist->alphabet_size variable can lead to reading memory beyond allocated buffer boundaries.

Critical Impact

Successful exploitation of this vulnerability could allow an attacker to read sensitive information from memory by crafting a malicious media file, potentially leading to information disclosure when a user processes the file with an affected FFmpeg version.

Affected Products

• FFmpeg versions prior to commit bf814387f42e9b0dea9d75c03db4723c88e7d962
• FFmpeg 6.1 and earlier releases without the security patch
• Applications and services utilizing vulnerable FFmpeg libraries for media processing

Discovery Timeline

• October 27, 2023 - CVE-2023-46407 published to NVD
• August 11, 2025 - Last updated in NVD database

Technical Details for CVE-2023-46407

Vulnerability Analysis

This vulnerability is classified as CWE-125 (Out-of-bounds Read), affecting FFmpeg's JPEG XL parser implementation. The flaw occurs within the read_vlc_prefix() function where the dist->alphabet_size variable is used without proper validation, allowing read operations to access memory locations outside the intended buffer boundaries.

The local attack vector requires user interaction—typically tricking a victim into opening a specially crafted media file. While the vulnerability does not allow code execution or data modification, it enables unauthorized disclosure of potentially sensitive memory contents, which could include cryptographic keys, authentication tokens, or other process data residing in adjacent memory regions.

Root Cause

The root cause stems from an uninitialized VLC (Variable Length Code) structure in the JPEG XL parser. The level1_vlc variable was not properly initialized before use, leading to undefined behavior when the dist->alphabet_size variable referenced memory locations. This regression introduced an out-of-bounds read condition that could be triggered when parsing malformed JPEG XL content.

Attack Vector

An attacker can exploit this vulnerability through the following attack flow:

1. Craft Malicious Media File: Create a specially crafted JPEG XL or media file that triggers the vulnerable code path in the VLC prefix reading function
2. Social Engineering: Distribute the malicious file through email attachments, web downloads, or media streaming services
3. Victim Interaction: When the victim opens or processes the file using FFmpeg or any application built with vulnerable FFmpeg libraries
4. Memory Disclosure: The out-of-bounds read occurs, potentially exposing sensitive process memory to the attacker

     int repeat_count_prev = 0, repeat_count_zero = 0, prev = 8;
     int total_code = 0, len, hskip, num_codes = 0, ret;
 
-    VLC level1_vlc;
+    VLC level1_vlc = { 0 };
 
     if (dist->alphabet_size == 1) {
         dist->vlc.bits = 0;

Source: GitHub Commit Update

The patch initializes the level1_vlc structure to zero, preventing the out-of-bounds read by ensuring all fields have known, safe values before any operations are performed.

Detection Methods for CVE-2023-46407

Indicators of Compromise

• Unexpected crashes or segmentation faults in FFmpeg-based applications when processing JPEG XL files
• Memory access violations logged by system monitoring tools during media file processing
• Unusual memory read patterns detected by runtime memory sanitizers (ASan, Valgrind)

Detection Strategies

• Deploy file integrity monitoring to detect suspicious media files being processed by FFmpeg instances
• Implement application-level logging to capture FFmpeg parsing errors and abnormal terminations
• Use memory safety tools in development and staging environments to identify out-of-bounds access attempts
• Monitor for unusual file types or malformed headers in media processing pipelines

Monitoring Recommendations

• Enable verbose logging in applications using FFmpeg to capture detailed error information during media processing
• Configure endpoint detection solutions to alert on repeated crashes of FFmpeg processes
• Implement sandboxing for media processing workflows to contain potential exploitation attempts
• Review application logs for patterns indicating attempts to trigger parser vulnerabilities

How to Mitigate CVE-2023-46407

Immediate Actions Required

• Update FFmpeg to a version containing commit bf814387f42e9b0dea9d75c03db4723c88e7d962 or later
• Audit all applications and services using FFmpeg libraries and schedule updates accordingly
• Implement input validation to filter potentially malicious media files before processing
• Consider temporarily disabling JPEG XL support if immediate patching is not possible

Patch Information

The vulnerability has been addressed in FFmpeg through commit bf814387f42e9b0dea9d75c03db4723c88e7d962. The fix properly initializes the level1_vlc VLC structure to zero before use, eliminating the out-of-bounds read condition.

Official patch resources:

• GitHub Commit Update
• FFmpeg Patch Submission (October 13, 2023)
• FFmpeg Patch Submission (October 15, 2023)

Workarounds

• Restrict media file processing to trusted sources until patches can be applied
• Implement sandboxed execution environments for FFmpeg processing tasks to limit potential impact
• Use network segmentation to isolate media processing systems from sensitive data repositories
• Deploy web application firewalls with rules to inspect and block potentially malicious media uploads

# Verify FFmpeg version and check if patch is applied
ffmpeg -version

# Check if the vulnerable commit is present in your build
git log --oneline | grep bf814387f42e9b0dea9d75c03db4723c88e7d962

# Compile FFmpeg from source with the latest security patches
git clone https://github.com/FFmpeg/FFmpeg.git
cd FFmpeg
./configure --enable-gpl --enable-version3
make -j$(nproc)
sudo make install