CVE-2017-8312 in VLC
Summary
by MITRE
Heap out-of-bound read in ParseJSS in VideoLAN VLC due to missing check of string length allows attackers to read heap uninitialized data via a crafted subtitles file.
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Analysis
by VulDB Data Team • 10/02/2020
The vulnerability CVE-2017-8312 represents a critical heap out-of-bounds read flaw within the VideoLAN VLC media player's JavaScript parsing component known as ParseJSS. This issue arises from insufficient validation of string length parameters during subtitle file processing, creating a scenario where maliciously crafted subtitle files can trigger unauthorized memory access patterns. The vulnerability specifically affects the handling of JavaScript subtitles within the VLC media player ecosystem, making it particularly dangerous for users who frequently process multimedia content from untrusted sources.
The technical root cause of this vulnerability stems from a missing bounds check in the string processing logic of the ParseJSS module. When VLC encounters a subtitle file containing JavaScript code, the parser fails to validate whether the input string length exceeds expected parameters before attempting to read memory locations. This oversight allows attackers to craft subtitle files that contain carefully constructed data sequences designed to trigger memory access beyond allocated heap boundaries. The flaw manifests as an uninitialized data read operation where the parser accesses memory locations that have not been properly initialized, potentially exposing sensitive information from other parts of the application's memory space.
From an operational perspective, this vulnerability poses significant risks to users who process multimedia content from untrusted sources or encounter maliciously crafted subtitle files. Attackers can exploit this flaw by preparing specially crafted subtitle files that, when loaded by VLC, cause the application to read uninitialized heap data and potentially leak sensitive information including cryptographic keys, user credentials, or other confidential data. The vulnerability is particularly concerning because it can be triggered through normal media playback operations without requiring any special privileges or user interaction beyond opening the malicious file. This makes it a prime candidate for drive-by attacks or supply chain compromises where malicious actors distribute compromised subtitle files through various channels.
The impact of this vulnerability extends beyond simple information disclosure, as it can potentially lead to more severe consequences including complete system compromise. The heap out-of-bounds read allows attackers to gain insights into memory layout and application state, which could facilitate further exploitation techniques such as information leakage attacks or memory corruption exploits. According to CWE classification, this vulnerability maps to CWE-125: Out-of-bounds Read, which is categorized under the broader class of buffer overflow vulnerabilities that can lead to unpredictable behavior and potential system compromise. The ATT&CK framework would classify this as a technique involving code injection through file processing, potentially leading to privilege escalation or lateral movement if combined with other exploitation vectors.
Mitigation strategies for CVE-2017-8312 should focus on immediate patching of affected VLC versions, as the vulnerability has been addressed through official security updates from VideoLAN. Organizations should implement strict content filtering policies for subtitle files, particularly those from untrusted sources, and consider disabling JavaScript subtitle processing entirely if not required for legitimate use cases. Network administrators should monitor for suspicious subtitle file downloads and implement sandboxing measures for media processing operations. The vulnerability also highlights the importance of input validation and bounds checking in multimedia processing libraries, emphasizing the need for comprehensive security testing of parsing components that handle external data inputs. Regular security updates and vulnerability assessments should be implemented to prevent similar issues in other media processing components within the broader VLC ecosystem and related software applications.