CVE-2009-4631 in FFmpeg
Summary
by MITRE
Off-by-one error in the VP3 decoder (vp3.c) in FFmpeg 0.5 allows remote attackers to cause a denial of service and possibly execute arbitrary code via a crafted VP3 file that triggers an out-of-bounds read and possibly memory corruption.
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Analysis
by VulDB Data Team • 04/30/2026
The vulnerability identified as CVE-2009-4631 represents a critical off-by-one error within the VP3 decoder component of FFmpeg version 0.5, demonstrating a classic buffer boundary violation that can be exploited remotely. This flaw exists in the vp3.c source file where the decoder fails to properly validate array indices during video frame processing, creating a condition where malicious input can cause the software to read memory locations beyond allocated buffers. The vulnerability falls under CWE-129, which specifically addresses improper validation of array indices, and aligns with ATT&CK technique T1203 for legitimate program exploitation through memory corruption. The VP3 video format decoder in FFmpeg processes compressed video data using a complex algorithm that involves multiple stages including motion compensation, transform decoding, and entropy decoding, making this particular flaw particularly dangerous as it can be triggered during normal playback operations.
The technical exploitation of this vulnerability occurs when a specially crafted VP3 file contains malformed data that causes the decoder to access memory beyond the bounds of allocated buffers during frame reconstruction. The off-by-one error specifically manifests when the decoder calculates array indices for motion vectors or coefficient storage, where an increment operation or boundary check fails to account for the full range of valid indices. This memory corruption can lead to unpredictable behavior including application crashes, denial of service conditions, or potentially arbitrary code execution if the corrupted memory locations contain executable code or if the corruption affects control flow structures. The vulnerability is particularly concerning because VP3 format was widely used in various multimedia applications and web browsers, making the attack surface extensive and the potential impact significant for users processing multimedia content.
The operational impact of CVE-2009-4631 extends beyond simple denial of service scenarios to include potential remote code execution capabilities that could be leveraged by attackers to compromise systems running vulnerable FFmpeg implementations. When exploited, this vulnerability can affect any application or service that utilizes FFmpeg for video processing, including web servers, content management systems, multimedia players, and streaming services. The vulnerability's remote exploitability means that attackers can deliver malicious VP3 files through various channels including email attachments, web downloads, or streaming services without requiring user interaction beyond opening the media file. This characteristic makes it particularly dangerous in enterprise environments where multimedia content is frequently processed and where the attack surface includes not just end-user systems but also server infrastructure that processes user-uploaded content. The vulnerability's presence in FFmpeg 0.5 indicates that it was present in a widely distributed multimedia processing library, amplifying its potential impact across numerous platforms and applications.
Mitigation strategies for CVE-2009-4631 focus on immediate patching of affected FFmpeg versions and implementation of input validation measures to prevent malformed VP3 files from reaching the vulnerable decoder. Organizations should prioritize updating to FFmpeg versions that contain the specific fix for this off-by-one error, typically available in versions 0.5.1 and later where proper boundary checks were implemented. System administrators should also implement content filtering mechanisms that validate media file integrity before processing, particularly for user-uploaded content or content from untrusted sources. Network-level protections can include implementing sandboxing techniques that isolate multimedia processing components from core system functions, and deploying intrusion detection systems that monitor for patterns associated with VP3 file processing. Additionally, security teams should conduct thorough vulnerability assessments of all systems that utilize FFmpeg or related multimedia libraries to ensure complete remediation and prevent similar issues in other components of the multimedia processing stack. The vulnerability serves as a reminder of the importance of rigorous input validation in multimedia decoders and the critical need for regular security updates in widely-used open source libraries.