CVE-2016-8676 in libav
Summary
by MITRE
The get_vlc2 function in get_bits.h in Libav 11.9 allows remote attackers to cause a denial of service (NULL pointer dereference and crash) via a crafted mp3 file. NOTE: this issue exists due to an incomplete fix for CVE-2016-8675.
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Analysis
by VulDB Data Team • 08/15/2020
The vulnerability identified as CVE-2016-8676 represents a critical denial of service flaw within the Libav multimedia framework version 11.9. This issue specifically targets the get_vlc2 function located in the get_bits.h header file, demonstrating how incomplete security patches can leave systems vulnerable to repeated exploitation. The flaw manifests when processing crafted mp3 files, creating a scenario where remote attackers can trigger a NULL pointer dereference that ultimately results in application crash and system unavailability. This vulnerability directly impacts the robustness and reliability of multimedia processing applications that depend on Libav for audio file handling, particularly those exposed to untrusted input streams.
The technical nature of this vulnerability stems from improper input validation within the variable length coding (VLC) decoding process that Libav employs for mp3 file parsing. When the get_vlc2 function encounters malformed mp3 data structures, it fails to properly validate pointer references before dereferencing them, leading to a NULL pointer exception. This behavior aligns with CWE-476 which categorizes NULL pointer dereference as a common programming error that can lead to application crashes and potential information disclosure. The vulnerability operates at the bitstream parsing layer where audio codecs decode compressed data, making it particularly dangerous as it can be exploited through standard network protocols without requiring special privileges or authentication.
From an operational standpoint, this vulnerability presents significant risks to services that process user-uploaded or externally sourced mp3 files, including media streaming platforms, content management systems, and multimedia applications. The remote exploitation capability means that attackers can trigger the denial of service condition from anywhere on the network without physical access to the target system. This makes the vulnerability particularly attractive for attackers seeking to disrupt services or perform availability attacks against multimedia infrastructure. The impact extends beyond simple service interruption as such crashes can potentially be leveraged as part of broader attack chains, especially when combined with other vulnerabilities in the same codebase or when the affected applications do not implement proper error handling and recovery mechanisms.
The vulnerability's relationship to CVE-2016-8675 demonstrates how security fixes can sometimes be incomplete or insufficient, creating a false sense of security while leaving underlying architectural issues unresolved. This pattern of incomplete remediation represents a common challenge in security maintenance where developers may address immediate symptoms without fully understanding root causes. Organizations using Libav 11.9 should implement immediate mitigation strategies including input validation, file format sanitization, and proper error handling mechanisms. Additionally, the ATT&CK framework categorizes this type of vulnerability under the T1499 sub-technique for Network Denial of Service, highlighting its potential for disrupting service availability. The recommended remediation involves upgrading to patched versions of Libav, implementing strict file validation before processing, and deploying intrusion detection systems that can identify suspicious mp3 file patterns. Security teams should also consider implementing network segmentation and access controls to limit the potential impact of such vulnerabilities in their environments.