CVE-2011-0522 in VLC Media Player
Summary
by MITRE
The StripTags function in (1) the USF decoder (modules/codec/subtitles/subsdec.c) and (2) the Text decoder (modules/codec/subtitles/subsusf.c) in VideoLAN VLC Media Player 1.1 before 1.1.6-rc allows remote attackers to execute arbitrary code via a subtitle with an opening "<" without a closing ">" in an MKV file, which triggers heap memory corruption, as demonstrated using refined-australia-blu720p-sample.mkv.
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Analysis
by VulDB Data Team • 01/18/2025
The vulnerability identified as CVE-2011-0522 represents a critical heap-based buffer overflow in VideoLAN VLC Media Player versions prior to 1.1.6-rc. This flaw exists within the subtitle processing functionality of the media player, specifically affecting both the USF decoder and Text decoder components. The vulnerability manifests when the StripTags function processes subtitle data from MKV files, creating a dangerous condition that can be exploited by remote attackers to execute arbitrary code on affected systems. The flaw is particularly concerning because it operates during the normal playback of media files, making exploitation possible through legitimate media consumption activities without requiring special privileges or user interaction beyond playing the malicious content.
The technical implementation of this vulnerability stems from inadequate input validation within the subtitle parsing logic. When VLC encounters a subtitle entry containing an opening angle bracket "<" character without a corresponding closing ">" bracket, the StripTags function fails to properly handle this malformed input. This condition leads to heap memory corruption as the function attempts to process the malformed data structure, causing memory allocation errors that can be manipulated by attackers to overwrite critical memory locations. The vulnerability specifically affects the USF decoder located in modules/codec/subtitles/subsdec.c and the Text decoder in modules/codec/subtitles/subsusf.c, both of which are part of VLC's core subtitle processing pipeline. The exploitation mechanism leverages the predictable nature of heap corruption to potentially overwrite function pointers or return addresses, enabling code execution.
The operational impact of CVE-2011-0522 extends beyond simple remote code execution, as it represents a significant security risk for any system running vulnerable versions of VLC Media Player. Attackers can craft malicious MKV files containing specially formatted subtitle data to trigger the vulnerability, making this a vector that could be exploited through various attack scenarios including malicious file sharing, compromised media servers, or targeted attacks against users who download content from untrusted sources. The vulnerability's exploitation does not require user interaction beyond normal media playback, making it particularly dangerous as users may unknowingly execute malicious code while simply watching videos. The heap corruption aspect of this vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and the code execution capability maps to CWE-787, representing out-of-bounds writes that can lead to arbitrary code execution.
Security practitioners should consider this vulnerability in the context of the MITRE ATT&CK framework, particularly under the T1059.007 technique for command and scripting interpreter and T1203 for Exploitation for Client Execution. The vulnerability demonstrates how media player applications can serve as attack vectors for privilege escalation and system compromise, as the code execution occurs within the context of the media player process. Organizations should prioritize immediate patching of VLC installations to version 1.1.6-rc or later, as this vulnerability has been widely exploited in the wild and represents a significant risk to end-user security. Additionally, network administrators should consider implementing content filtering measures to prevent the distribution of potentially malicious MKV files, particularly in environments where users may be exposed to untrusted media content. The vulnerability underscores the importance of proper input validation in multimedia processing libraries and highlights the need for robust memory safety mechanisms in media player applications to prevent similar issues in future implementations.