CVE-2018-19839 in LibSass
Summary
by MITRE
In LibSass prior to 3.5.5, the function handle_error in sass_context.cpp allows attackers to cause a denial-of-service resulting from a heap-based buffer over-read via a crafted sass file.
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Analysis
by VulDB Data Team • 06/12/2023
The vulnerability identified as CVE-2018-19839 represents a critical heap-based buffer over-read flaw within LibSass version 3.5.4 and earlier. This issue exists within the handle_error function located in the sass_context.cpp source file, which serves as a core component of the LibSass library responsible for processing sass files. The vulnerability stems from inadequate input validation and memory management during error handling operations, creating a scenario where maliciously crafted sass files can trigger unintended memory access patterns. Attackers can exploit this weakness by constructing specially formatted sass input that causes the library to read beyond allocated memory boundaries, leading to system instability and potential denial-of-service conditions. The flaw specifically manifests when the library processes error conditions in a manner that does not properly bounds-check memory accesses, allowing for arbitrary memory reads beyond the intended buffer limits. This vulnerability directly impacts the stability and reliability of applications that depend on LibSass for css compilation, particularly those processing untrusted sass content from external sources. The security implications extend beyond simple service disruption as the over-read behavior could potentially expose sensitive memory contents or facilitate more sophisticated exploitation techniques. According to CWE classification, this vulnerability maps to CWE-125: Out-of-bounds Read, which specifically addresses situations where programs access memory beyond the boundaries of allocated buffers. The ATT&CK framework categorizes this as a Denial of Service attack vector through memory corruption, falling under the technique of process injection and memory manipulation. The vulnerability affects systems where LibSass is integrated into web applications, build systems, or development environments that compile sass files without proper input sanitization. Applications utilizing LibSass for dynamic css generation, particularly those accepting user-generated content or external sass inputs, face significant risk. The exploitation requires minimal privileges and can be executed through simple file manipulation, making it particularly dangerous in automated build processes or web applications that compile sass on-the-fly. The fix for this vulnerability required implementing proper bounds checking within the handle_error function to prevent memory access beyond allocated buffer boundaries. Security researchers recommend immediate patching of affected systems to prevent exploitation, as the vulnerability does not require elevated privileges to trigger and can be easily weaponized by attackers. Organizations should also implement input validation measures and consider sandboxing sass compilation processes to limit potential impact. The vulnerability highlights the importance of proper memory management in C++ applications and underscores the need for comprehensive testing of error handling paths in library code. Regular security assessments of third-party dependencies should include examination of memory safety aspects to prevent similar issues from affecting production systems. The remediation process involves updating to LibSass version 3.5.5 or later, which includes fixed memory management routines and enhanced input validation that properly handle edge cases in error conditions.