CVE-2017-18246 in libav
Summary
by MITRE
The pcm_encode_frame function in libavcodec/pcm.c in Libav 12.2 allows remote attackers to cause a denial of service (heap-based buffer over-read) via a crafted media file.
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Analysis
by VulDB Data Team • 01/16/2020
The vulnerability identified as CVE-2017-18246 represents a critical heap-based buffer over-read flaw within the Libav multimedia framework version 12.2. This issue resides in the pcm_encode_frame function located in the libavcodec/pcm.c source file, where improper input validation and boundary checking allows maliciously crafted media files to trigger unauthorized memory access patterns. The flaw specifically affects the handling of PCM (Pulse Code Modulation) audio encoding operations, making it particularly dangerous for applications that process audio content from untrusted sources. Attackers can exploit this vulnerability by preparing a specially crafted media file that, when processed by the vulnerable Libav library, causes the application to read beyond the allocated heap memory boundaries.
The technical implementation of this vulnerability stems from inadequate validation of input parameters within the PCM encoding pipeline. When the pcm_encode_frame function processes audio data, it fails to properly verify the size and structure of the incoming PCM frames, allowing attackers to craft input sequences that exceed the expected buffer limits. This over-read condition occurs during the frame encoding process where the function attempts to access memory locations that have not been properly allocated or are outside the intended data boundaries. The heap-based nature of the vulnerability indicates that the memory corruption happens within dynamically allocated heap segments rather than stack-based memory areas, making the exploitation more complex but equally dangerous. The vulnerability manifests as a denial of service condition where the application crashes or becomes unresponsive due to the memory access violation.
The operational impact of CVE-2017-18246 extends beyond simple service disruption to potentially enable more sophisticated attack vectors. Applications that utilize Libav for multimedia processing, including media players, streaming services, content management systems, and digital asset processing tools, become vulnerable to remote exploitation. This vulnerability can be leveraged by attackers to cause widespread service outages across systems that depend on Libav for audio processing functionality. The remote nature of the attack means that adversaries can exploit this flaw without requiring local access to the target system, making it particularly concerning for web-based applications and services that handle user-uploaded media content. The vulnerability affects the integrity of the application's memory space and can potentially lead to information disclosure or further exploitation if combined with other vulnerabilities.
Mitigation strategies for CVE-2017-18246 primarily focus on immediate remediation through version updates and input validation enhancements. Organizations should prioritize upgrading to Libav versions that contain patches addressing this specific buffer over-read condition, typically found in versions released after the vulnerability disclosure. The patch implementation involves adding proper bounds checking and input validation within the pcm_encode_frame function to ensure that all PCM frame data remains within allocated memory boundaries. Additionally, implementing robust input sanitization measures at the application level can provide defense-in-depth protection, including media file format validation, size limitation checks, and content scanning for suspicious patterns. System administrators should also consider deploying network-based intrusion detection systems that can identify and block suspicious media file patterns associated with known exploitation attempts. This vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and may map to ATT&CK technique T1059 for remote code execution through application exploitation, emphasizing the need for comprehensive security posture management and regular vulnerability assessment programs.
The vulnerability demonstrates the critical importance of proper memory management in multimedia processing libraries, where buffer overflows and over-read conditions can have severe operational consequences. The flaw highlights the need for thorough code review processes and automated testing frameworks that can identify memory safety issues in complex multimedia processing pipelines. Organizations relying on Libav or similar multimedia frameworks must implement continuous monitoring and vulnerability management procedures to ensure timely patch deployment and prevent exploitation of similar memory safety issues in their software ecosystems.