CVE-2016-9823 in libav
Summary
by MITRE
libavcodec/x86/mpegvideo.c in libav 11.8 allows remote attackers to cause a denial of service (crash) via a crafted file.
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Analysis
by VulDB Data Team • 09/03/2020
The vulnerability identified as CVE-2016-9823 resides within the libavcodec library, specifically in the x86/mpegvideo.c file of libav version 11.8. This issue represents a critical denial of service vulnerability that can be exploited by remote attackers through the careful crafting of media files. The libav library serves as a comprehensive multimedia framework that handles various audio and video codecs, making it a fundamental component in many media processing applications and systems. When a maliciously constructed file is processed by this library, the vulnerability manifests as an application crash or system instability, effectively rendering the affected software unusable for its intended purpose.
The technical flaw stems from inadequate input validation within the MPEG video decoding routines. The vulnerability occurs during the parsing and processing of specific MPEG video frames where the code fails to properly validate the structure and content of incoming data. This particular weakness allows attackers to construct media files containing malformed or unexpected data sequences that trigger buffer overflows, invalid memory access patterns, or other critical execution errors within the decoder. The issue is particularly concerning because it operates at the codec level, meaning that any application relying on libav for video processing could be affected, regardless of the application's own security measures. The vulnerability can be triggered through various attack vectors including web browsers, media players, or any system that processes video content using the affected library.
The operational impact of CVE-2016-9823 extends beyond simple system crashes, potentially affecting a wide range of applications and services that utilize the libav library. This includes web browsers that support video playback, media servers, content management systems, and various multimedia applications. The vulnerability's remote exploitability means that attackers can potentially compromise systems without requiring local access or user interaction beyond the simple act of opening or processing a malicious file. In enterprise environments, this could lead to widespread service disruption, particularly in systems that automatically process or stream video content. The vulnerability also presents challenges for security teams as it can be difficult to detect and prevent, since the malicious files appear legitimate until they are processed by the vulnerable library.
Mitigation strategies for CVE-2016-9823 primarily involve immediate patching of the affected libav library to version 11.9 or later, where the vulnerability has been resolved through improved input validation and error handling mechanisms. System administrators should prioritize updating all applications and services that depend on libav, particularly those handling untrusted media content. Network-based mitigations can include implementing content filtering and sanitization procedures for video files, though these approaches are not foolproof given the nature of the vulnerability. The fix implemented by the developers typically involves adding additional checks to validate frame structures and memory boundaries during MPEG video decoding, preventing the execution path that leads to the crash condition. Organizations should also consider implementing runtime protections such as address space layout randomization and stack canaries to add additional layers of defense. This vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and can be mapped to ATT&CK technique T1203, involving legitimate user execution through exploitation of vulnerabilities in applications. The vulnerability demonstrates the critical importance of maintaining up-to-date multimedia libraries and implementing robust input validation practices in security-sensitive applications.