CVE-2009-4639 in FFmpeg
Summary
by MITRE
The av_rescale_rnd function in the AVI demuxer in FFmpeg 0.5 allows remote attackers to cause a denial of service (crash) via a crafted AVI file that triggers a divide-by-zero error.
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Analysis
by VulDB Data Team • 04/30/2026
The vulnerability identified as CVE-2009-4639 represents a critical denial of service flaw within the FFmpeg multimedia framework's AVI demuxer component. This issue specifically affects version 0.5 of FFmpeg, where the av_rescale_rnd function demonstrates a problematic handling of certain mathematical operations that can lead to system instability. The vulnerability manifests when processing maliciously crafted AVI files that contain malformed data structures designed to exploit the divide-by-zero condition inherent in the function's implementation. The AVI demuxer serves as a crucial component for parsing and extracting audio and video streams from AVI container format files, making this vulnerability particularly dangerous as it can be triggered through routine media file processing operations.
The technical root cause of this vulnerability lies in the improper validation and handling of parameters within the av_rescale_rnd function, which is responsible for scaling audio and video sample rates during demuxing operations. When the demuxer encounters an AVI file containing specially constructed metadata or stream parameters, the function attempts to perform a division operation where the denominator becomes zero, resulting in an immediate system crash or termination of the processing application. This divide-by-zero error occurs because the function fails to validate incoming stream parameters before executing mathematical operations, allowing malformed data to propagate through the processing pipeline. The vulnerability demonstrates a classic lack of input sanitization and error handling that aligns with CWE-369, which specifically addresses the issue of divide-by-zero conditions in software implementations.
The operational impact of CVE-2009-4639 extends beyond simple system crashes, as it can be leveraged by remote attackers to disrupt services that depend on FFmpeg for media processing. Any application or service utilizing FFmpeg 0.5 for AVI file handling becomes vulnerable to this attack vector, including media servers, content management systems, and multimedia processing applications. The vulnerability can be exploited through various attack scenarios including web-based file uploads, automated media processing pipelines, or even through embedded media players that utilize FFmpeg as their underlying multimedia engine. The remote nature of this attack means that an attacker can trigger the vulnerability without requiring local system access, making it particularly concerning for publicly accessible services. This flaw can lead to complete service disruption, resource exhaustion, and potential denial of service conditions that affect legitimate users and system availability.
Mitigation strategies for CVE-2009-4639 primarily focus on immediate version upgrades to patched versions of FFmpeg where the divide-by-zero condition has been addressed through proper input validation and error handling mechanisms. System administrators should prioritize updating their FFmpeg installations to versions that contain fixes for this vulnerability, typically found in FFmpeg releases following version 0.5. Additionally, implementing input validation measures at the application level can provide an additional layer of protection by sanitizing AVI file parameters before they reach the FFmpeg demuxer. Network-level filtering and sandboxing approaches can also help contain the impact of such vulnerabilities by limiting the scope of potential exploitation. Organizations should consider implementing automated patch management processes to ensure timely deployment of security updates. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service, and the T1203 technique for exploitation of software vulnerabilities, highlighting the need for comprehensive security posture management that includes both preventive and detective controls to address such remote code execution and denial of service threats in multimedia processing environments.