CVE-2017-18243 in libav
Summary
by MITRE
The unpack_parse_unit function in libavcodec/dirac_parser.c in Libav 12.2 allows remote attackers to cause a denial of service (segmentation fault) via a crafted file.
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Analysis
by VulDB Data Team • 01/15/2020
The vulnerability identified as CVE-2017-18243 resides within the libavcodec library, specifically in the dirac_parser.c component that handles Dirac video stream parsing. This flaw manifests as a remote code execution risk that can be exploited through crafted media files, potentially leading to system instability and denial of service conditions. The affected version libav 12.2 represents a widely used multimedia processing library that forms part of numerous applications and systems handling video content, making this vulnerability particularly concerning from a security perspective.
The technical root cause of this vulnerability lies in the unpack_parse_unit function which fails to properly validate input parameters during the parsing of Dirac video streams. When processing specially crafted files, the function does not adequately check array bounds or memory access patterns, leading to a segmentation fault during execution. This type of flaw falls under the category of buffer over-read conditions as defined by CWE-129, where the application attempts to read memory beyond allocated boundaries. The vulnerability represents a classic example of improper input validation that allows attackers to manipulate memory access patterns through malicious file structures.
From an operational standpoint, this vulnerability presents significant risks to systems that process video content from untrusted sources. Attackers can exploit this weakness by preparing specially crafted Dirac video files that, when processed by vulnerable applications, trigger the segmentation fault and cause system crashes. The impact extends beyond simple denial of service as the vulnerability may potentially be leveraged in more sophisticated attacks where multiple system components are affected. The vulnerability affects applications using libavcodec for video decoding including media players, streaming servers, and content processing systems that handle Dirac format video streams.
The exploitation of this vulnerability aligns with ATT&CK technique T1203, which involves gaining access to systems through the manipulation of input data to cause system instability. Security practitioners should consider this vulnerability as part of a broader attack surface analysis, particularly in environments where media processing occurs. Organizations utilizing libav or derivative libraries such as ffmpeg should prioritize patching and updating their systems to prevent potential exploitation. The recommended mitigation strategy involves immediate deployment of updated libav versions that contain fixes for the buffer over-read condition in the dirac_parser.c file, alongside implementing proper input validation measures and sandboxing techniques for untrusted media content processing.
The broader implications of this vulnerability highlight the importance of robust input validation in multimedia processing libraries, which are often targeted due to their complex parsing requirements and the diverse range of file formats they must handle. This flaw demonstrates how seemingly benign parsing operations can become security risks when proper bounds checking and memory management practices are not implemented. Security teams should monitor for similar patterns in other multimedia libraries and ensure comprehensive testing of input validation mechanisms in all file processing components. The vulnerability serves as a reminder of the critical need for regular security assessments of multimedia processing systems and the importance of maintaining up-to-date software versions to protect against known exploits.