CVE-2018-18827 in libav
Summary
by MITRE
There exists a heap-based buffer over-read in ff_vc1_pred_dc in vc1_block.c in Libav 12.3, which allows attackers to cause a denial-of-service via a crafted aac file.
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Analysis
by VulDB Data Team • 04/07/2020
The vulnerability identified as CVE-2018-18827 represents a critical heap-based buffer over-read flaw within the Libav multimedia framework version 12.3. This issue specifically affects the ff_vc1_pred_dc function located in the vc1_block.c source file, which is responsible for processing digital video compression in the VC-1 video codec standard. The flaw manifests when processing maliciously crafted AAC audio files, demonstrating how audio processing components can inadvertently trigger memory corruption issues in video decoding libraries. Such cross-component vulnerabilities highlight the complex interdependencies within multimedia processing frameworks where errors in one codec can affect the processing of entirely different media formats.
The technical nature of this vulnerability stems from improper bounds checking within the VC-1 video decoding logic. When the ff_vc1_pred_dc function attempts to read data from a heap-allocated buffer, it fails to validate the boundaries of the memory access, allowing an attacker to craft an AAC file that triggers an over-read condition. This occurs because the function assumes certain data structures or buffer sizes that may not be properly validated when processing malformed input. The vulnerability operates at the memory management level where insufficient input validation leads to memory access violations that can cause the application to crash or behave unpredictably. This type of flaw falls under the CWE-125 category of Out-of-Bounds Read, which is classified as a fundamental memory safety issue that can lead to system instability.
The operational impact of CVE-2018-18827 extends beyond simple denial-of-service conditions, as it represents a potential pathway for more sophisticated attacks within multimedia processing environments. An attacker could leverage this vulnerability to cause application crashes in media players, streaming services, or content processing pipelines that utilize Libav for video decoding. The vulnerability's exploitation requires crafting a specific AAC file that triggers the buffer over-read condition, making it a targeted attack vector rather than a widespread issue. However, the potential for cascading failures exists in environments where multiple media processing components interact, as the denial-of-service condition could disrupt legitimate media processing workflows. This vulnerability aligns with ATT&CK technique T1059.007 for application execution through media processing, where adversaries might use such flaws to disrupt services or create conditions for more complex attacks.
Mitigation strategies for CVE-2018-18827 should focus on immediate software updates and input validation improvements. The most effective approach involves upgrading to a patched version of Libav where the buffer over-read condition has been addressed through proper bounds checking and memory management. Organizations should implement comprehensive input validation for all media files processed through Libav, including signature verification and format consistency checks to prevent malformed files from reaching the vulnerable code path. Additionally, deployment of runtime protections such as address space layout randomization and stack canaries can help mitigate potential exploitation scenarios. Security monitoring should include detection of unusual application crashes or memory access patterns that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of proper memory management in multimedia libraries and the need for thorough input validation across all processing components.