CVE-2019-6286 in LibSass
Summary
by MITRE
In LibSass 3.5.5, a heap-based buffer over-read exists in Sass::Prelexer::skip_over_scopes in prelexer.hpp when called from Sass::Parser::parse_import(), a similar issue to CVE-2018-11693.
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Analysis
by VulDB Data Team • 06/27/2023
The vulnerability identified as CVE-2019-6286 represents a critical heap-based buffer over-read flaw within the LibSass library version 3.5.5. This issue resides in the Sass::Prelexer::skip_over_scopes function located in the prelexer.hpp file, which is invoked during the Sass::Parser::parse_import() processing sequence. The vulnerability demonstrates a concerning pattern of memory safety issues within the Sass parsing infrastructure, particularly when handling import directives in stylesheet files. The flaw stems from insufficient bounds checking when processing certain input patterns, allowing an attacker to potentially read memory beyond the allocated buffer boundaries. This type of vulnerability falls under the CWE-125 weakness category, which specifically addresses out-of-bounds read conditions that can lead to information disclosure or system compromise.
The technical exploitation of this vulnerability occurs when the prelexer attempts to process complex or malformed import statements within sass stylesheet files. During the parsing operation, the skip_over_scopes function fails to properly validate the boundaries of memory operations, causing the parser to read beyond the intended buffer limits. When the Sass::Parser::parse_import() function calls this vulnerable code path, it creates an opportunity for attackers to craft malicious input that triggers the over-read condition. The heap-based nature of the vulnerability means that the memory corruption occurs in the heap allocation area rather than on the stack, making it particularly challenging to detect and exploit. This vulnerability aligns with ATT&CK technique T1059.001 for execution through script-based attacks and T1555.003 for credential access through memory manipulation.
The operational impact of CVE-2019-6286 extends beyond simple memory corruption, potentially enabling attackers to extract sensitive information from adjacent memory locations. This could include cached credentials, cryptographic keys, or other confidential data stored in the application's memory space. The vulnerability affects systems that utilize LibSass for stylesheet compilation, particularly those running web applications that process user-supplied sass files or import directives. Attackers could leverage this flaw to perform reconnaissance activities, gather system information, or potentially escalate privileges within affected environments. The similarity to CVE-2018-11693 indicates a persistent pattern of buffer over-read issues within the LibSass parsing engine, suggesting that the underlying memory management logic requires comprehensive review and remediation. Organizations using sass-based build systems, web frameworks, or static site generators that depend on LibSass should consider this vulnerability as a high-priority concern for their security posture.
Mitigation strategies for CVE-2019-6286 should focus on immediate patching of the LibSass library to version 3.5.6 or later, where the buffer over-read has been addressed through proper bounds checking implementation. System administrators should also implement input validation controls at multiple layers, including web application firewalls and content filtering mechanisms that can detect and block suspicious import patterns. Additionally, organizations should consider implementing memory safety monitoring tools and runtime protections such as address space layout randomization and stack canaries to reduce the exploitability of similar vulnerabilities. The fix for this vulnerability typically involves adding proper boundary checks in the skip_over_scopes function to ensure that memory reads remain within allocated buffer limits. Security teams should also conduct thorough code reviews of any custom sass processing logic and monitor for similar patterns that might indicate other potential buffer over-read conditions within the application stack.