CVE-2019-6283 in LibSass
Summary
by MITRE
In LibSass 3.5.5, a heap-based buffer over-read exists in Sass::Prelexer::parenthese_scope in prelexer.hpp.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 06/27/2023
The vulnerability identified as CVE-2019-6283 represents a critical heap-based buffer over-read flaw within LibSass version 3.5.5, a widely-used C++ library for compiling Sass stylesheets to CSS. This issue resides in the Sass::Prelexer::parenthese_scope function located within the prelexer.hpp header file, making it a fundamental component of the Sass processing pipeline that handles parsing of parentheses and scope boundaries. The vulnerability arises from insufficient bounds checking during the parsing of complex nested parentheses structures, creating a scenario where memory reads extend beyond allocated buffer boundaries. This type of vulnerability falls under CWE-125, which specifically addresses out-of-bounds read conditions in software systems.
The technical implementation of this flaw occurs when LibSass processes Sass code containing deeply nested or malformed parentheses structures that exceed the expected buffer capacity. During the parsing phase, the prelexer function attempts to read memory locations beyond the allocated heap buffer, potentially accessing sensitive data from adjacent memory regions or causing application crashes through segmentation faults. The vulnerability is particularly concerning because it operates within the core parsing logic that handles fundamental syntactic elements of the Sass language, making it exploitable through maliciously crafted Sass input files that could be processed by applications using LibSass. This issue demonstrates poor memory management practices and inadequate input validation in the prelexer component that should have been protected against buffer over-read conditions.
The operational impact of CVE-2019-6283 extends beyond simple application crashes, as it creates potential security risks in environments where LibSass processes untrusted input from external sources. Attackers could potentially exploit this vulnerability to extract sensitive information from memory, cause denial-of-service conditions, or in more sophisticated scenarios, potentially execute arbitrary code through memory corruption. The vulnerability affects web applications, static site generators, and build systems that rely on LibSass for CSS compilation, particularly those processing user-generated content or external stylesheet inputs. Given the widespread adoption of LibSass in modern web development workflows and the prevalence of automated build processes, this vulnerability could be leveraged in supply chain attacks or web application exploitation scenarios, making it a significant concern for security-conscious organizations. The ATT&CK framework categorizes this as a memory corruption vulnerability that could enable privilege escalation or information disclosure through improper input handling.
Mitigation strategies for CVE-2019-6283 require immediate patching of LibSass to version 3.6.0 or later, where the buffer over-read issue has been resolved through proper bounds checking and memory management improvements. Organizations should also implement input validation measures that sanitize Sass code before processing, particularly when handling external or user-generated content. Additional defensive measures include deploying runtime protections such as address space layout randomization and stack canaries to mitigate potential exploitation attempts, along with monitoring for unusual memory access patterns that might indicate exploitation attempts. Security teams should conduct thorough vulnerability assessments of systems using LibSass to identify potential attack surfaces and implement network segmentation to limit the impact of successful exploitation attempts. The fix implemented in newer LibSass versions demonstrates proper adherence to secure coding practices by ensuring all buffer operations are properly bounded and validated, addressing the underlying CWE-125 vulnerability through comprehensive code review and testing procedures.