CVE-2016-7499 in libav
Summary
by MITRE
The sbr_make_f_master function in aacsbr.c in Libav 11.7 allows remote attackers to cause a denial of service (divide-by-zero error and application crash) via a crafted mp3 file.
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Analysis
by VulDB Data Team • 08/15/2020
The vulnerability identified as CVE-2016-7499 represents a critical divide-by-zero error within the sbr_make_f_master function of the aacsbr.c file in Libav version 11.7. This flaw exists within the audio decoding subsystem responsible for processing Advanced Audio Coding (AAC) files, specifically affecting the spectral band replication processing component that handles frequency domain signal reconstruction. The vulnerability manifests when the Libav library processes specially crafted mp3 files that contain malformed spectral band replication data, triggering an arithmetic exception during the frequency bin calculation process. This divide-by-zero condition occurs when the function attempts to perform mathematical operations using a zero value as a divisor, which is a fundamental violation of mathematical principles and results in immediate system termination.
The technical implementation of this vulnerability stems from insufficient input validation within the audio decoding pipeline where the sbr_make_f_master function fails to properly validate the spectral band replication parameters before performing mathematical operations. The function processes frequency domain data that should contain valid scaling factors and frequency bin configurations, but when malformed data is encountered, the validation logic does not adequately check for zero values in critical calculation variables. This represents a classic example of improper input validation and error handling, which aligns with CWE-369, a weakness category that encompasses divide-by-zero errors and related arithmetic exceptions. The flaw is particularly concerning as it demonstrates a lack of robust error handling in audio processing libraries that are widely deployed across various media applications and operating systems.
Operationally, this vulnerability creates a significant denial of service risk for any system utilizing Libav 11.7 for audio processing, particularly in environments where users might encounter untrusted media files. Attackers can exploit this weakness by crafting malicious mp3 files that contain specially formatted spectral band replication data designed to trigger the zero division condition during playback or processing. When such a file is processed by an application built on Libav, the application crashes immediately upon encountering the divide-by-zero error, resulting in a complete service disruption. This type of vulnerability is particularly dangerous in streaming applications, media servers, or any automated processing systems where continuous operation is critical, as the crash can be leveraged to create persistent availability issues. The attack vector is straightforward and requires minimal skill to execute, making it a preferred target for adversaries seeking to disrupt audio services.
The impact of this vulnerability extends beyond simple service disruption to potentially enable more sophisticated attacks when combined with other exploitation techniques. System administrators and developers should consider this vulnerability in the context of broader security frameworks, particularly when analyzing application stability and resilience against malformed inputs. The flaw demonstrates the importance of implementing comprehensive input validation and robust error handling in multimedia processing libraries, as these components often serve as foundational elements for numerous applications. Security practitioners should note that this vulnerability aligns with ATT&CK technique T1499.001, which covers network denial of service attacks, and represents a classic example of how seemingly benign input processing can result in system-wide availability failures. Organizations should prioritize updating their Libav installations to versions that contain proper input validation and error handling mechanisms to prevent exploitation of this divide-by-zero condition and maintain system integrity in audio processing environments.