CVE-2017-9991 in FFmpeg
Summary
by MITRE
Heap-based buffer overflow in the xwd_decode_frame function in libavcodec/xwddec.c in FFmpeg before 2.8.12, 3.0.x before 3.0.8, 3.1.x before 3.1.8, 3.2.x before 3.2.5, and 3.3.x before 3.3.1 allows remote attackers to cause a denial of service (application crash) or possibly have unspecified other impact via a crafted file.
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Analysis
by VulDB Data Team • 12/09/2022
The vulnerability identified as CVE-2017-9991 represents a critical heap-based buffer overflow affecting the FFmpeg multimedia framework's X11 Window Dump (xwd) decoder component. This flaw exists within the xwd_decode_frame function located in libavcodec/xwddec.c and impacts multiple versions of FFmpeg including 2.8.x series before 2.8.12, 3.0.x series before 3.0.8, 3.1.x series before 3.1.8, 3.2.x series before 3.2.5, and 3.3.x series before 3.3.1. The vulnerability arises from insufficient input validation when processing specially crafted XWD image files, creating conditions where maliciously constructed data can overwrite adjacent memory regions in the heap.
The technical nature of this vulnerability stems from improper bounds checking within the xwd decoding logic, where the application fails to adequately validate the size parameters of XWD file headers before allocating memory for frame data. When a maliciously crafted XWD file is processed, the decoder attempts to allocate heap memory based on malformed size fields contained within the file structure, leading to a situation where the allocated buffer is insufficient to contain the actual data being read. This fundamental flaw in memory management allows attackers to write beyond the allocated buffer boundaries, potentially corrupting adjacent heap metadata or other critical application data structures.
From an operational perspective, this vulnerability presents significant risks to systems that process untrusted multimedia content through FFmpeg libraries. Remote attackers can exploit this weakness by crafting malicious XWD files that, when opened by applications using vulnerable FFmpeg versions, trigger application crashes and denial of service conditions. The impact extends beyond simple service disruption as the heap corruption could potentially enable more sophisticated attacks depending on the execution environment and memory layout. The vulnerability's classification under CWE-121 heap-based buffer overflow indicates it follows a well-known pattern of memory safety issues that have historically led to privilege escalation and arbitrary code execution in similar scenarios. Security researchers have noted that such buffer overflows in multimedia decoders often provide attack vectors for remote code execution when combined with other vulnerabilities or when the target environment lacks modern exploit mitigations like stack canaries or address space layout randomization.
The exploitation of this vulnerability demonstrates the importance of input validation and memory safety practices in multimedia processing libraries that handle untrusted content. Organizations using FFmpeg for video processing, streaming, or content conversion services are particularly at risk, as these applications often process files from unknown sources without proper sanitization. The vulnerability aligns with ATT&CK technique T1203 (Exploitation for Client Execution) and T1068 (Exploitation for Privilege Escalation) when considering potential escalation paths. Mitigation strategies should focus on immediate patching of affected FFmpeg versions, implementing strict input validation at application layers, and deploying network-based intrusion detection systems to monitor for suspicious XWD file processing activities. Additionally, organizations should consider implementing sandboxing mechanisms and privilege separation for multimedia processing components to limit potential impact from successful exploitation attempts.