CVE-2015-8661 in FFmpeg
Summary
by MITRE
The h264_slice_header_init function in libavcodec/h264_slice.c in FFmpeg before 2.8.3 does not validate the relationship between the number of threads and the number of slices, which allows remote attackers to cause a denial of service (out-of-bounds array access) or possibly have unspecified other impact via crafted H.264 data.
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Analysis
by VulDB Data Team • 07/01/2022
The vulnerability identified as CVE-2015-8661 resides within the FFmpeg multimedia framework's handling of H.264 video streams, specifically in the h264_slice_header_init function located in libavcodec/h264_slice.c. This flaw represents a classic buffer overflow condition that occurs when the software fails to properly validate input parameters during video decoding operations. The issue affects FFmpeg versions prior to 2.8.3, making it a significant concern for systems that rely on this widely-used open-source multimedia processing library for video content handling. The vulnerability stems from inadequate validation of the relationship between thread count and slice count parameters, creating a scenario where maliciously crafted H.264 data can trigger unexpected behavior in the decoding process.
The technical implementation of this vulnerability involves the improper handling of slice header initialization within H.264 video streams. When FFmpeg processes video data containing crafted slice information, the h264_slice_header_init function does not verify that the number of threads specified in the video stream corresponds appropriately with the number of slices present. This mismatch creates a condition where array bounds are exceeded during memory access operations, leading to potential out-of-bounds memory access. The flaw operates at the intersection of multimedia processing and memory management, where the expected relationship between parallel processing threads and video slice structures is violated. According to CWE classification, this represents a CWE-129: Improper Validation of Array Index vulnerability, where the software fails to validate that array indices are within acceptable ranges.
The operational impact of CVE-2015-8661 extends beyond simple denial of service conditions to potentially encompass more severe consequences including arbitrary code execution. Remote attackers can exploit this vulnerability by crafting malicious H.264 video content that, when processed by vulnerable FFmpeg implementations, triggers the out-of-bounds memory access condition. This vulnerability is particularly dangerous in environments where FFmpeg is used for video processing, streaming services, or content delivery networks, as it can be leveraged to disrupt services or potentially gain unauthorized access to systems. The attack surface is broad given FFmpeg's widespread adoption across various platforms and applications, including web browsers, media players, and server-side video processing systems. From an ATT&CK framework perspective, this vulnerability maps to T1059.007: Command and Scripting Interpreter: Python and T1499.004: Network Denial of Service, representing both execution and availability attack vectors.
Mitigation strategies for CVE-2015-8661 primarily involve upgrading to FFmpeg version 2.8.3 or later, where the validation issue has been addressed through proper bounds checking of thread and slice relationship parameters. System administrators should implement comprehensive patch management procedures to ensure all FFmpeg installations are updated promptly. Additionally, input validation measures can be implemented at network boundaries or application levels to filter suspicious H.264 content before processing. Organizations should also consider implementing runtime protections such as address space layout randomization and stack canaries to reduce the exploitability of similar vulnerabilities. The remediation process should include thorough testing of updated systems to ensure that the patch does not introduce compatibility issues with existing video processing workflows, while also monitoring for any potential side effects in video decoding performance or quality.