CVE-2017-12964 in LibSass
Summary
by MITRE
There is a stack consumption issue in LibSass 3.4.5 that is triggered in the function Sass::Eval::operator() in eval.cpp. It will lead to a remote denial of service attack.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 11/09/2019
The vulnerability identified as CVE-2017-12964 represents a critical stack consumption issue within LibSass version 3.4.5, a widely used C++ library for compiling Sass stylesheet files into CSS. This flaw manifests within the Sass::Eval::operator() function located in the eval.cpp source file, where excessive stack memory consumption occurs during the evaluation of certain Sass expressions. The issue arises from insufficient stack depth validation during recursive operations, creating a scenario where maliciously crafted Sass input can trigger rapid stack exhaustion. The vulnerability is particularly concerning as it exists within a component that is fundamental to web development toolchains, making it accessible to attackers who can manipulate Sass compilation processes through web applications or build systems.
The technical exploitation of this vulnerability occurs when the Sass evaluation engine processes nested or complex expressions that result in deep recursion without adequate stack management. The flaw allows an attacker to craft specific Sass code that causes the evaluation function to consume excessive stack memory during recursive operations, ultimately leading to stack overflow conditions. This behavior aligns with CWE-772, which describes insufficient resource pool sizing, and demonstrates how improper stack usage in recursive algorithms can create denial of service conditions. The vulnerability can be triggered remotely through web applications that compile Sass files, making it particularly dangerous in server-side rendering environments where user input is processed through the Sass compilation pipeline.
The operational impact of CVE-2017-12964 extends beyond simple service disruption, as it enables remote attackers to perform denial of service attacks against systems running LibSass versions prior to 3.4.6. When exploited, the vulnerability can cause application crashes, process termination, and complete service unavailability for legitimate users. This affects web applications, static site generators, and build systems that rely on LibSass for stylesheet compilation, potentially impacting thousands of applications and developers. The vulnerability's remote exploitation capability means that attackers do not require local access to the system, making it a significant risk for web-facing applications. From an attack framework perspective, this vulnerability maps to ATT&CK technique T1499.004, which covers network denial of service, and demonstrates how memory consumption issues can be leveraged for system availability compromise.
Mitigation strategies for CVE-2017-12964 primarily focus on updating to LibSass version 3.4.6 or later, where the stack consumption issue has been resolved through improved recursive depth management and stack usage monitoring. Organizations should conduct comprehensive inventory assessments to identify all systems using vulnerable LibSass versions and implement patch management procedures to ensure timely updates. Additionally, implementing input validation and sanitization measures for Sass compilation processes can provide defensive layers against exploitation attempts. System administrators should consider monitoring stack usage patterns and implementing resource limits for compilation processes to reduce the impact of potential exploitation attempts. The vulnerability highlights the importance of proper resource management in recursive algorithms and demonstrates the critical need for thorough testing of memory consumption patterns in development libraries used in production environments.