CVE-2026-64830 in FFmpeg
Summary
by MITRE • 07/22/2026
FFmpeg versions 2.1 through 8.1.2 contains a heap buffer overflow vulnerability in the VobSub subtitle demuxer that allows attackers to corrupt adjacent heap memory by supplying a malicious .sub/.idx subtitle file declaring more distinct stream IDs than the fixed-size array bounds in libavformat/mpeg.c. Attackers can craft a subtitle file with excessive distinct stream IDs to trigger unbounded writes beyond the vobsub->q[] array boundary via ff_subtitles_queue_insert(), potentially achieving arbitrary code execution in any application using FFmpeg's VobSub demuxer.
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Analysis
by VulDB Data Team • 07/22/2026
This heap buffer overflow vulnerability exists within FFmpeg's VobSub subtitle demuxer implementation across versions 2.1 through 8.1.2, representing a critical security flaw that can lead to remote code execution when processing malicious subtitle files. The vulnerability stems from inadequate bounds checking in the subtitle parsing logic where the vobsub->q[] array has fixed size constraints but the demuxer fails to validate the number of distinct stream IDs declared in .sub/.idx files. This weakness specifically manifests in libavformat/mpeg.c where the ff_subtitles_queue_insert() function performs unbounded writes beyond the allocated array boundary, allowing attackers to overwrite adjacent heap memory locations.
The technical exploitation of this vulnerability follows a straightforward yet dangerous pattern where an attacker crafts a malicious subtitle file containing more distinct stream IDs than the fixed-size vobsub->q[] array can accommodate. When FFmpeg processes such a file through its VobSub demuxer, the excessive stream ID count triggers the buffer overflow condition during the subtitle queue insertion operation. This unbounded memory write behavior creates opportunities for attackers to manipulate heap metadata, overwrite function pointers, or inject malicious code into adjacent memory regions, effectively bypassing standard memory protection mechanisms.
The operational impact of this vulnerability extends beyond simple memory corruption as it can be leveraged in various attack scenarios including remote code execution within applications that utilize FFmpeg for media processing. Any software system relying on FFmpeg's VobSub demuxer for handling subtitle files becomes susceptible to this exploit, particularly applications serving user-uploaded content or processing untrusted media files from external sources. The vulnerability is especially concerning in web applications, media servers, and content management systems where automated media processing workflows may inadvertently execute malicious subtitle parsing operations.
Security mitigations for this vulnerability require immediate version upgrades to FFmpeg releases that contain the patched implementation of the VobSub demuxer with proper bounds checking mechanisms. System administrators should implement strict input validation procedures for subtitle files and consider deploying sandboxed processing environments when handling untrusted media content. Additionally, organizations should establish comprehensive patch management protocols to ensure timely deployment of security updates across all FFmpeg-dependent applications. This vulnerability aligns with CWE-121 heap-based buffer overflow and can be classified under ATT&CK technique T1059 for command and script injection, emphasizing the need for robust input sanitization and memory safety practices in multimedia processing libraries.
The root cause of this vulnerability demonstrates a classic software security flaw where insufficient boundary validation leads to exploitable memory corruption conditions. The fixed-size array allocation pattern combined with unvalidated user input creates an ideal scenario for heap-based attacks that can be executed through carefully crafted malicious files. This type of vulnerability is particularly dangerous because it operates at the core processing layer of multimedia applications, making it difficult to detect and prevent through traditional network-level security measures. Organizations should prioritize comprehensive code review processes focusing on buffer management and memory safety practices when implementing or integrating multimedia processing libraries into their systems.
This vulnerability represents a significant risk to digital media ecosystems where subtitle files are commonly used without proper validation of their contents. The ease with which attackers can trigger this condition through simple file manipulation makes it an attractive target for exploit development, particularly in environments where FFmpeg is integrated into automated processing workflows or web applications handling user-generated content. Security researchers recommend implementing multiple layers of defense including input sanitization, memory protection mechanisms, and regular security auditing of multimedia processing components to prevent exploitation of similar buffer overflow conditions in other parts of the software stack.