CVE-2021-25802 in VLC Media Player
Summary
by MITRE • 07/26/2021
A buffer overflow vulnerability in the AVI_ExtractSubtitle component of VideoLAN VLC Media Player 3.0.11 allows attackers to cause an out-of-bounds read via a crafted .avi file.
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Analysis
by VulDB Data Team • 08/05/2021
The vulnerability CVE-2021-25802 represents a critical buffer overflow flaw within the AVI_ExtractSubtitle component of VideoLAN VLC Media Player version 3.0.11. This issue stems from inadequate input validation when processing specially crafted .avi media files that contain maliciously constructed subtitle data. The vulnerability manifests as an out-of-bounds read condition that occurs during the parsing of AVI container files, specifically when the player attempts to extract subtitle information from malformed media streams. Such buffer overflows typically arise when applications fail to properly bounds-check data read from external sources before processing or storing it in memory buffers. The flaw exists in the subtitle extraction logic where the application does not adequately verify the size or structure of subtitle data contained within the AVI file format, leading to memory access violations when the player attempts to process the crafted input. This vulnerability falls under the CWE-121 category of stack-based buffer overflow, though the specific implementation details suggest it operates as a more complex memory corruption issue that can lead to arbitrary code execution or denial of service conditions.
The operational impact of this vulnerability extends beyond simple media playback disruption as it creates a potential attack vector for remote code execution or system compromise. When a user opens a maliciously crafted .avi file through VLC Media Player, the buffer overflow can trigger unpredictable behavior including application crashes, memory corruption, or even allow attackers to inject and execute arbitrary code on the target system. The attack scenario typically involves social engineering tactics where users are tricked into opening specially crafted media files that contain the malicious subtitle data designed to exploit this buffer overflow. The vulnerability is particularly concerning because VLC Media Player is widely distributed and used across multiple platforms including Windows, macOS, Linux, and mobile operating systems, making the potential attack surface extensive. Security researchers have noted that the vulnerability can be exploited through various attack vectors including web-based delivery, email attachments, or file sharing platforms where users might unknowingly open infected media files. The out-of-bounds read condition specifically targets the subtitle extraction component which is commonly used in multimedia applications and can be triggered even when users simply play media files without any explicit interaction with subtitle features.
Mitigation strategies for CVE-2021-25802 should prioritize immediate software updates and patches from VideoLAN, as the vendor has released versions that address this specific vulnerability in their media player software. System administrators and end users must ensure they are running patched versions of VLC Media Player, specifically versions 3.0.12 or later, which contain the necessary fixes for the buffer overflow condition. Organizations should implement strict file validation policies and consider deploying network-based intrusion detection systems that can identify and block malicious media file content. Security teams should also consider implementing sandboxing techniques when processing untrusted media files, particularly in environments where users may be exposed to potentially malicious content. Additionally, users should be educated about the risks of opening media files from untrusted sources and should be trained to recognize potential social engineering attempts that might lead to exploitation of this vulnerability. The ATT&CK framework categorizes this vulnerability under T1203 - Exploitation for Client Execution, where attackers leverage media player vulnerabilities to execute malicious code on target systems. Organizations should also consider implementing automated patch management systems to ensure all instances of VLC Media Player across their network are updated promptly. Regular security assessments should include scanning for vulnerable versions of VLC Media Player and monitoring for any attempts to exploit this buffer overflow through network traffic analysis or endpoint detection and response systems.