CVE-2018-20001 in libav
Summary
by MITRE
In Libav 12.3, there is a floating point exception in the range_decode_culshift function (called from range_decode_bits) in libavcodec/apedec.c that will lead to remote denial of service via crafted input.
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Analysis
by VulDB Data Team • 04/19/2020
The vulnerability identified as CVE-2018-20001 represents a critical floating point exception within the Libav multimedia framework version 12.3, specifically affecting the range_decode_culshift function located in the libavcodec/apedec.c file. This flaw manifests when the function is invoked through the range_decode_bits calling sequence, creating a scenario where malformed input data can trigger an unexpected floating point operation that results in program termination. The vulnerability operates at the intersection of multimedia processing and memory management, where the decoder fails to properly validate input parameters before executing mathematical operations that could lead to arithmetic exceptions.
The technical exploitation of this vulnerability requires an attacker to craft specially formatted media files that contain malicious data structures designed to trigger the specific floating point exception within the range_decode_culshift function. When the Libav library processes such crafted input, the function attempts to perform bit manipulation operations that result in invalid floating point states, causing the application to crash and terminate unexpectedly. This behavior constitutes a remote denial of service condition as the vulnerability can be triggered through network-delivered media content without requiring local system access. The flaw demonstrates poor error handling and input validation practices within the audio decoding component, particularly in how it processes compressed audio data formats.
The operational impact of CVE-2018-20001 extends beyond simple service disruption, as it represents a fundamental weakness in the robustness of multimedia processing libraries that are widely deployed across various applications and systems. Any software utilizing Libav version 12.3 for audio decoding capabilities becomes vulnerable to this remote denial of service attack, potentially affecting media players, streaming services, content processing applications, and other systems that rely on this library for audio format support. The vulnerability's classification aligns with CWE-191, which addresses integer underflow conditions, and demonstrates characteristics consistent with ATT&CK technique T1499.004 for network denial of service attacks. Organizations deploying affected systems face significant risk as this vulnerability can be exploited by malicious actors to disrupt services without requiring elevated privileges or specialized access.
Mitigation strategies for CVE-2018-20001 primarily focus on immediate software updates and patches provided by the Libav development community, as well as implementing input validation measures at application layers that utilize the affected library. System administrators should prioritize updating to patched versions of Libav where available, while organizations may need to consider temporary workarounds such as restricting media file types processed by affected applications or implementing additional validation layers before media processing occurs. The vulnerability highlights the importance of robust error handling in multimedia libraries and demonstrates the need for comprehensive testing of edge cases in audio decoding functions. Security monitoring should include detection of unusual application termination patterns and potential exploitation attempts targeting multimedia processing components, as this vulnerability can serve as an initial access vector for more sophisticated attacks targeting systems that rely heavily on multimedia processing capabilities.