CVE-2019-19721 in VLC Media Player
Summary
by MITRE
An off-by-one error in the DecodeBlock function in codec/sdl_image.c in VideoLAN VLC media player before 3.0.9 allows remote attackers to cause a denial of service (memory corruption) via a crafted image file. NOTE: this may be related to the SDL_Image product.
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Analysis
by VulDB Data Team • 05/16/2020
The vulnerability identified as CVE-2019-19721 represents a critical memory corruption issue within the VideoLAN VLC media player software ecosystem. This flaw exists in the DecodeBlock function located within the codec/sdl_image.c file, specifically affecting versions prior to 3.0.9. The vulnerability manifests as an off-by-one error, a common class of programming defect that occurs when a loop or buffer operation exceeds its intended boundaries by a single element. Such errors typically arise from improper boundary checking in array or buffer operations where the condition for iteration or access includes an extra element beyond the allocated memory space.
The technical implementation of this vulnerability involves the SDL_Image library integration within VLC's media processing pipeline, where the DecodeBlock function handles the decoding of image data from various formats. When processing maliciously crafted image files, the off-by-one error causes the function to access memory locations beyond the allocated buffer boundaries, leading to memory corruption. This type of error can result in unpredictable program behavior, application crashes, or potentially more severe consequences depending on the memory layout and the specific nature of the corruption. The vulnerability's classification under CWE-129 (Improper Validation of Array Index) and CWE-131 (Incorrect Calculation of Buffer Size) demonstrates its fundamental nature as a buffer overflow condition that occurs due to inadequate input validation and boundary checking.
From an operational perspective, this vulnerability poses significant risks to users who may encounter crafted malicious image files through various attack vectors including email attachments, web downloads, or file sharing networks. The remote exploitation capability means that attackers can trigger the denial of service condition without requiring local access to the target system, making it particularly dangerous in environments where VLC is used for media processing. The memory corruption can lead to complete application crashes, rendering the media player unusable until restarted, which constitutes a denial of service condition that can be exploited to disrupt user activities or potentially serve as a stepping stone for more sophisticated attacks. According to ATT&CK framework, this vulnerability maps to T1203 (Exploitation for Client Execution) and T1499 (Endpoint Denial of Service) techniques, as it enables remote code execution through application instability and service disruption.
The mitigation strategy for CVE-2019-19721 centers on immediate software updates to VLC version 3.0.9 or later, which contains the necessary patches to address the buffer boundary checking issue. Organizations should implement comprehensive patch management procedures to ensure all instances of VLC are updated promptly, particularly in environments where the software processes untrusted media content. Additional defensive measures include implementing content filtering mechanisms to scan and validate image files before processing, employing sandboxing techniques to isolate media processing operations, and configuring network security controls to prevent access to potentially malicious content. System administrators should also monitor for unusual application behavior or crash patterns that might indicate exploitation attempts. The vulnerability highlights the importance of robust input validation and boundary checking in multimedia processing libraries, as demonstrated by the relationship to SDL_Image product components that require careful attention to memory management practices. Security teams should consider this vulnerability as part of broader media processing security assessments, particularly in environments where media files are frequently processed from external sources or user-generated content.