CVE-2009-4633 in FFmpeg
Summary
by MITRE
vorbis_dec.c in FFmpeg 0.5 uses an assignment operator when a comparison operator was intended, which might allow remote attackers to cause a denial of service and possibly execute arbitrary code via a crafted file that modifies a loop counter and triggers a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 04/30/2026
The vulnerability identified as CVE-2009-4633 represents a critical software flaw within the FFmpeg multimedia framework version 0.5, specifically within the vorbis_dec.c file responsible for decoding Vorbis audio formats. This issue stems from a fundamental programming error where an assignment operator was mistakenly employed in place of a comparison operator, creating a dangerous condition that can be exploited by malicious actors. The flaw manifests when processing specially crafted audio files that manipulate loop counter variables, ultimately leading to unpredictable behavior within the decoding process.
The technical implementation of this vulnerability involves a classic programming error that falls under CWE-481, which addresses the improper assignment of boolean values. When the assignment operator is used instead of the comparison operator, the conditional logic becomes fundamentally flawed, causing the loop counter to be modified in unintended ways. This misconfiguration allows attackers to craft malicious audio files that, when processed by FFmpeg, trigger a cascade of events leading to heap-based buffer overflow conditions. The heap corruption occurs because the loop counter modification causes the decoder to allocate memory incorrectly or access memory locations beyond the intended buffer boundaries.
From an operational perspective, this vulnerability presents significant risks to systems that process multimedia content through FFmpeg, particularly in environments where user-uploaded files are handled without proper validation. The potential impact extends beyond simple denial of service to include arbitrary code execution capabilities, making it a severe security concern for web applications, media servers, and content delivery networks. Attackers can leverage this flaw to crash applications, potentially leading to system instability, data corruption, or in worst-case scenarios, complete system compromise. The vulnerability affects any system running FFmpeg 0.5 or earlier versions that process Vorbis audio files, making it particularly dangerous in widespread deployment scenarios.
The exploitation of this vulnerability aligns with techniques described in the ATT&CK framework under the T1203 category for Obfuscated Files or Information, as attackers can craft malicious files that appear legitimate but contain the specific programming error triggers. Organizations should prioritize immediate remediation by upgrading to FFmpeg versions that have patched this issue, as the vulnerability exists in the core decoding logic and cannot be effectively mitigated through configuration changes alone. Additionally, implementing input validation and sanitization measures for multimedia content, along with regular security updates and vulnerability assessments, remains crucial for protecting against similar issues in other components of the multimedia processing pipeline. The vulnerability demonstrates the critical importance of code review processes and automated static analysis tools in identifying such subtle but dangerous programming errors that can have far-reaching security implications across multiple systems and applications.