CVE-2018-11693 in LibSaas
Summary
by MITRE
An issue was discovered in LibSaas through 3.5.4. An out-of-bounds read of a memory region was found in the function Sass::Prelexer::skip_over_scopes which could be leveraged by an attacker to disclose information or manipulated to read from unmapped memory causing a denial of service.
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Analysis
by VulDB Data Team • 03/21/2023
The vulnerability identified as CVE-2018-11693 resides within the LibSass library version 3.5.4 and earlier, representing a critical out-of-bounds memory read flaw that fundamentally compromises the library's memory safety mechanisms. This issue manifests specifically within the Sass::Prelexer::skip_over_scopes function, which serves as a crucial component in the preprocessing phase of Sass stylesheet compilation. The flaw occurs when the library processes malformed input data that triggers improper boundary checking during scope parsing operations, creating a scenario where the application attempts to access memory locations beyond the allocated buffer boundaries.
The technical exploitation of this vulnerability follows a well-defined pattern that aligns with CWE-125, which describes out-of-bounds read conditions in software implementations. When the Sass::Prelexer::skip_over_scopes function encounters malformed input sequences, it fails to properly validate array indices or buffer limits, leading to memory access violations. This memory corruption can result in two distinct operational impacts that attackers can leverage for different objectives. The first impact involves information disclosure, where the out-of-bounds read may expose sensitive data from adjacent memory regions, potentially including stack contents, heap data, or other confidential information stored in memory proximity to the vulnerable function execution context.
The second operational impact occurs when the memory access violation results in a denial of service condition, specifically causing the application to crash or terminate unexpectedly. This occurs when the out-of-bounds read attempts to access unmapped memory regions that are not allocated to the process, triggering segmentation faults or access violations that terminate the executing program. This behavior directly maps to ATT&CK technique T1499.004, which describes the use of memory corruption to cause denial of service conditions in software systems.
From a security perspective, this vulnerability represents a significant risk to applications that rely on LibSass for stylesheet processing, particularly web applications that accept user-provided CSS or Sass content. The attack surface expands when considering that many web frameworks and content management systems utilize LibSass for dynamic styling, making the exploitation potential widespread. The vulnerability's impact extends beyond simple denial of service as it can potentially be chained with other memory corruption flaws to achieve more sophisticated attacks including arbitrary code execution, though the immediate risk lies in the information disclosure and service disruption capabilities. The flaw's exploitation requires minimal privileges and can be accomplished through carefully crafted input that triggers the specific parsing path within the prelexer component.
Mitigation strategies for CVE-2018-11693 primarily focus on immediate remediation through version updates to LibSass 3.5.5 and later releases where the out-of-bounds read has been patched. Organizations should conduct comprehensive vulnerability assessments to identify all systems utilizing affected LibSass versions and implement patch management procedures to ensure timely deployment of security fixes. Additionally, input validation measures should be enhanced at application boundaries to filter potentially malicious Sass content before processing, providing defense-in-depth protection against exploitation attempts. The vulnerability serves as a reminder of the critical importance of memory safety practices in C++ based libraries and the necessity of thorough boundary checking mechanisms in parsing functions that handle user-supplied data.