CVE-2017-11341 in LibSass
Summary
by MITRE
There is a heap based buffer over-read in lexer.hpp of LibSass 3.4.5. A crafted input will lead to a remote denial of service attack.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 09/08/2025
The vulnerability identified as CVE-2017-11341 represents a critical heap-based buffer over-read flaw within the LibSass library version 3.4.5. This issue resides in the lexer.hpp component, which serves as the lexical analyzer responsible for parsing Sass syntax into tokens that the compiler can process. The flaw arises from insufficient input validation and boundary checking during the tokenization process, creating a scenario where maliciously crafted input can cause the application to read memory beyond the allocated buffer boundaries. Such buffer over-read conditions typically occur when the parser attempts to access memory locations that have not been properly allocated or have already been freed, potentially leading to unpredictable behavior and system instability.
The technical execution of this vulnerability involves a remote attacker who can construct specific input sequences that trigger the buffer over-read condition within the LibSass lexer. When the library processes this crafted input, the parsing logic fails to properly validate the boundaries of memory allocations, allowing the program to access adjacent memory regions. This flaw can be exploited through various attack vectors including web applications that utilize LibSass for CSS compilation, build systems that incorporate the library, or any software that depends on LibSass for processing Sass files. The over-read condition typically manifests as a segmentation fault or memory access violation that causes the application to crash, thereby enabling a denial of service attack against the target system.
From an operational impact perspective, this vulnerability poses significant risks to web applications and development environments that rely on LibSass for CSS preprocessing. The remote denial of service aspect means that attackers can potentially disrupt services by causing applications to crash or become unresponsive, leading to availability issues for end users. The vulnerability affects systems where LibSass is integrated into web frameworks, static site generators, or build pipelines, making it particularly dangerous in production environments where continuous availability is critical. Security researchers have classified this issue under CWE-125, which specifically addresses out-of-bounds read vulnerabilities, and it aligns with ATT&CK technique T1499.004 for network denial of service attacks. The impact extends beyond simple service disruption as the over-read condition could potentially expose sensitive information from adjacent memory locations, though the primary concern remains the denial of service aspect.
Mitigation strategies for CVE-2017-11341 primarily focus on upgrading to patched versions of LibSass where the buffer over-read issue has been addressed through proper input validation and boundary checking. Organizations should immediately update their LibSass dependencies to versions 3.5.0 or later, which contain the necessary fixes for this vulnerability. Additionally, implementing input sanitization measures at the application level can provide an additional layer of protection by validating and filtering user-supplied Sass content before it reaches the LibSass parser. Security monitoring should include detection of unusual memory access patterns and segmentation faults that may indicate exploitation attempts. The fix typically involves strengthening the lexer's boundary checking mechanisms and ensuring that all memory access operations are properly validated against allocated buffer sizes. Organizations should also consider implementing network segmentation and access controls to limit exposure of systems that utilize LibSass, particularly those that process untrusted input from web users or external sources. Regular security assessments and dependency updates remain crucial for maintaining defense in depth against similar vulnerabilities in the software supply chain.