CVE-2018-6621 in FFmpeg
Summary
by MITRE
The decode_frame function in libavcodec/utvideodec.c in FFmpeg through 3.4.1 allows remote attackers to cause a denial of service (out of array read) via a crafted AVI file.
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Analysis
by VulDB Data Team • 02/03/2023
The vulnerability identified as CVE-2018-6621 represents a critical buffer over-read flaw within the FFmpeg multimedia framework that affects versions through 3.4.1. This issue resides in the decode_frame function located in the libavcodec/utvideodec.c source file, which is responsible for decoding UT Video format video streams. The vulnerability manifests when processing maliciously crafted AVI files that contain specially constructed UT Video data, creating a scenario where the decoder attempts to read beyond the allocated memory boundaries. Such out-of-bounds memory access occurs during the frame decoding process when the software fails to properly validate the size parameters of video data structures before accessing array elements. The flaw stems from insufficient input validation and boundary checking mechanisms within the video decoding pipeline, allowing attackers to manipulate the decoding process through carefully crafted file contents.
The technical exploitation of this vulnerability requires an attacker to prepare a malicious AVI file containing malformed UT Video data that triggers the buffer over-read condition. When a vulnerable FFmpeg instance processes this crafted file, the decode_frame function executes without proper bounds checking, causing memory access violations that result in application crashes or unpredictable behavior. This type of vulnerability falls under CWE-125, which specifically addresses out-of-bounds read conditions in software implementations. The operational impact extends beyond simple denial of service since such vulnerabilities can potentially be leveraged in more sophisticated attack scenarios. The flaw demonstrates a classic weakness in memory safety practices where array indices are not properly validated against array boundaries before access operations. This vulnerability is particularly concerning because FFmpeg is widely integrated into numerous applications, media players, and content management systems, making the potential attack surface extensive across multiple platforms and use cases.
The security implications of CVE-2018-6621 align with ATT&CK technique T1203, which involves the exploitation of software vulnerabilities to achieve system compromise. The vulnerability creates a pathway for attackers to disrupt services through denial of service attacks, potentially affecting media processing applications, content delivery networks, and multimedia platforms that rely on FFmpeg for video handling. Remote attackers can leverage this flaw without requiring any special privileges or authentication, making it particularly dangerous in environments where users might unknowingly open malicious media files. The vulnerability's impact is amplified by the widespread adoption of FFmpeg across various software ecosystems including web browsers, media players, streaming platforms, and content management systems. Organizations utilizing FFmpeg in their infrastructure should consider this vulnerability as a critical threat that could enable attackers to disrupt services or potentially escalate to more severe exploits if combined with other vulnerabilities. The flaw represents a fundamental issue in input validation practices and highlights the importance of robust memory safety mechanisms in multimedia processing libraries.
The recommended mitigation strategy involves immediate upgrade to FFmpeg version 3.4.2 or later, where the vulnerability has been addressed through proper bounds checking implementation in the decode_frame function. System administrators should also implement additional protective measures such as input validation at network boundaries, sandboxing of media processing components, and regular security assessments of multimedia handling systems. Organizations should consider implementing network segmentation to limit exposure and establish monitoring protocols to detect potential exploitation attempts. The fix typically involves adding proper array boundary checks and input validation before memory access operations, ensuring that all buffer access operations are validated against legitimate data sizes. This vulnerability serves as a reminder of the critical importance of maintaining up-to-date multimedia libraries and implementing comprehensive security practices in media processing environments, particularly given the widespread use of FFmpeg across various software platforms and applications.