CVE-2018-19826 in LibSass
Summary
by MITRE
In inspect.cpp in LibSass 3.5.5, a high memory footprint caused by an endless loop (containing a Sass::Inspect::operator()(Sass::String_Quoted*) stack frame) may cause a Denial of Service via crafted sass input files with stray '&' or '/' characters.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability CVE-2018-19826 represents a critical denial of service flaw within LibSass version 3.5.5, specifically within the inspect.cpp component. This issue manifests as an excessive memory consumption pattern that originates from an infinite loop mechanism within the Sass::Inspect::operator() function when processing certain string quoted objects. The flaw is particularly concerning because it can be triggered through carefully crafted sass input files containing stray '&' or '/' characters, making it exploitable via user-supplied content.
The technical root cause of this vulnerability lies in the improper handling of string quoted objects during the inspection phase of sass processing. When the parser encounters specific combinations of '&' and '/' characters within quoted strings, the inspection routine enters an infinite loop that continuously consumes memory resources. This behavior stems from the absence of proper loop termination conditions within the Sass::Inspect::operator()(Sass::String_Quoted*) stack frame, causing the memory footprint to grow uncontrollably until system resources are exhausted. The vulnerability is classified as a CWE-835: Loop with Unreachable Exit Condition (Infinite Loop) and maps to ATT&CK technique T1499.004: Network Denial of Service, as it can be leveraged to consume system resources and render services unavailable.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it can be exploited by attackers to perform remote denial of service attacks against systems processing sass content. This includes web applications, build systems, and static site generators that utilize LibSass for css compilation. The vulnerability is particularly dangerous in environments where sass files are processed from untrusted sources, such as user-uploaded content or third-party libraries. The infinite loop behavior can cause applications to become unresponsive, leading to complete service disruption and potentially affecting multiple concurrent users or processes. Systems running on limited hardware resources or containerized environments are especially vulnerable to this attack vector.
Mitigation strategies for CVE-2018-19826 involve immediate upgrading to LibSass version 3.5.6 or later, which contains the necessary patches to prevent the infinite loop condition. Organizations should also implement input validation and sanitization measures to filter out potentially malicious sass content before processing. Additionally, deploying resource limits and monitoring systems can help detect and prevent excessive memory consumption patterns. The fix addresses the underlying CWE-835 issue by implementing proper loop termination conditions and adding bounds checking to prevent the recursive inspection process from entering infinite execution paths. Security teams should also consider implementing automated scanning tools to identify and remediate vulnerable LibSass installations within their infrastructure, particularly in continuous integration pipelines and web application environments that process user-generated sass content.