CVE-2019-6284 in LibSass
Summary
by MITRE
In LibSass 3.5.5, a heap-based buffer over-read exists in Sass::Prelexer::alternatives in prelexer.hpp.
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Analysis
by VulDB Data Team • 06/27/2023
The vulnerability identified as CVE-2019-6284 represents a critical heap-based buffer over-read flaw within LibSass version 3.5.5, a popular C++ library used for compiling Sass stylesheet files into CSS. This issue resides in the Sass::Prelexer::alternatives function located within the prelexer.hpp header file, making it a fundamental component of the Sass parsing infrastructure that processes complex stylesheet syntax. The vulnerability manifests when the prelexer attempts to handle certain malformed input patterns that exceed expected buffer boundaries during lexical analysis operations.
The technical implementation of this flaw involves improper boundary checking within the alternatives parsing routine that processes multiple alternative patterns in Sass syntax. When encountering specific input sequences that trigger the parsing logic, the function reads memory beyond allocated buffer limits, potentially exposing sensitive data or causing application instability. This over-read condition occurs because the prelexer does not adequately validate input length against available buffer capacity before performing memory access operations. The vulnerability is particularly concerning as it operates within the core parsing engine that translates human-readable Sass syntax into machine-executable CSS output, making it a prime target for exploitation in code injection scenarios.
From an operational impact perspective, this vulnerability poses significant risks to web applications and development environments that rely on LibSass for stylesheet compilation. Attackers could potentially exploit this flaw to read sensitive memory contents, including cryptographic keys, user credentials, or application data that might be stored in adjacent memory locations. The over-read condition could also lead to application crashes or denial of service scenarios, disrupting legitimate service operations. Given that LibSass is widely used in web development frameworks and static site generators, the potential attack surface extends across numerous applications and platforms that depend on Sass compilation. The vulnerability aligns with CWE-125, which specifically addresses out-of-bounds read conditions, and represents a classic example of insufficient boundary checking in memory management operations.
The exploitation of CVE-2019-6284 typically requires an attacker to craft specific input patterns that trigger the vulnerable parsing path within LibSass, making it a targeted vulnerability rather than a broad-based exploit. Security researchers have noted that the vulnerability can be leveraged in conjunction with other memory corruption issues to achieve more sophisticated attack vectors, including arbitrary code execution in certain scenarios. Mitigation strategies should focus on immediate patching of LibSass to version 3.5.6 or later, which includes the necessary boundary checks to prevent the over-read condition. Organizations should also implement input validation measures and consider sandboxing compilation processes to limit potential impact. The vulnerability demonstrates the importance of proper memory management in parsing libraries and aligns with ATT&CK technique T1059.001 for executing malicious code through script injection, though in this case the attack vector is through malformed input rather than direct code injection.