CVE-2018-19219 in LibSass
Summary
by MITRE
In LibSass 3.5-stable, there is an illegal address access at Sass::Eval::operator that will lead to a DoS attack.
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Analysis
by VulDB Data Team • 09/08/2025
The vulnerability identified as CVE-2018-19219 represents a critical memory access issue within the LibSass CSS preprocessor library version 3.5-stable. This flaw exists within the Sass::Eval::operator function which is responsible for evaluating Sass expressions during the compilation process. The vulnerability manifests as an illegal address access pattern that occurs when the parser encounters specific malformed input sequences within Sass code. This type of memory corruption vulnerability falls under the category of improper input validation and memory management errors that can be exploited to cause system instability.
The technical implementation of this vulnerability stems from inadequate bounds checking and memory access validation within the evaluation engine of LibSass. When the Sass::Eval::operator function processes certain input patterns, it fails to properly validate memory pointers or array indices, leading to attempts to access memory locations that are either unmapped or protected. This improper memory access results in segmentation faults or access violations that terminate the application process. The vulnerability is particularly concerning because it can be triggered through user-supplied Sass code, making it exploitable in environments where untrusted input is processed, such as web applications or automated build systems.
From an operational perspective, this vulnerability creates significant denial of service risks for systems that rely on LibSass for CSS compilation. The impact extends beyond simple application crashes to potentially affect entire web services or development environments that depend on Sass processing capabilities. Attackers could exploit this vulnerability by crafting malicious Sass code that when processed by the affected library would cause the compilation process to terminate unexpectedly. This vulnerability has been classified under CWE-125 as "Out-of-bounds Read" and aligns with ATT&CK technique T1499.004 for "Network Denial of Service" as it can be leveraged to disrupt service availability through controlled input manipulation.
The exploitation of this vulnerability requires minimal privileges and can be executed through normal Sass compilation workflows, making it particularly dangerous in production environments. Systems utilizing LibSass for automated CSS processing, including content management systems, web application frameworks, or continuous integration pipelines, are at risk. The vulnerability demonstrates a fundamental flaw in the library's error handling and memory management practices, highlighting the importance of robust input validation in parsing libraries. Organizations should prioritize updating to patched versions of LibSass, implementing input sanitization measures, and monitoring for potential exploitation attempts that could disrupt service availability. The vulnerability also underscores the need for comprehensive testing of parsing libraries against malformed inputs to prevent similar issues in other components of the software supply chain.