CVE-2022-43358 in LibSass
Summary
by MITRE • 08/22/2023
Stack overflow vulnerability in ast_selectors.cpp: in function Sass::ComplexSelector::has_placeholder in libsass:3.6.5-8-g210218, which can be exploited by attackers to cause a denial of service (DoS).
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Analysis
by VulDB Data Team • 09/14/2023
The vulnerability identified as CVE-2022-43358 represents a critical stack overflow condition within the libsass library version 3.6.5-8-g210218, specifically manifesting in the Sass::ComplexSelector::has_placeholder function located in ast_selectors.cpp. This flaw occurs when processing malformed CSS selector inputs that trigger recursive parsing operations, ultimately leading to excessive stack consumption and potential program termination. The issue stems from inadequate input validation and bounds checking within the selector processing logic, creating a scenario where maliciously crafted CSS content can cause the application to crash or become unresponsive.
The technical exploitation of this vulnerability involves triggering the recursive parsing behavior through carefully constructed CSS selectors that contain nested or deeply nested pseudo-selectors and placeholder references. When the Sass::ComplexSelector::has_placeholder function processes these inputs, it fails to properly validate the depth of nested structures, allowing the stack to grow uncontrollably until it overflows. This particular flaw falls under CWE-129, which addresses insufficient validation of the length or size of input data, and more specifically aligns with CWE-787, concerning out-of-bounds write operations that can occur during recursive processing. The vulnerability demonstrates characteristics consistent with the attack pattern described in MITRE ATT&CK technique T1499.004, which involves resource exhaustion attacks targeting application stability through memory manipulation.
The operational impact of CVE-2022-43358 extends beyond simple denial of service, as it can be leveraged in broader attack scenarios involving web applications that utilize libsass for CSS processing. Applications such as static site generators, content management systems, and web development tools that rely on this library for style compilation become vulnerable to malicious input injection attacks. The vulnerability particularly affects environments where user-supplied CSS content is processed without proper sanitization, creating opportunities for attackers to exploit the stack overflow condition through crafted CSS files or dynamic content injection. This makes the vulnerability especially dangerous in multi-tenant environments or applications that accept arbitrary CSS input from untrusted sources.
Mitigation strategies for this vulnerability require immediate implementation of input validation measures and library version updates to address the core stack overflow condition. Organizations should prioritize updating to libsass versions that contain fixed implementations of the ComplexSelector::has_placeholder function, ensuring that recursive parsing operations include proper depth limits and stack consumption monitoring. Additionally, implementing input sanitization at the application level can provide defense-in-depth measures by filtering or rejecting CSS content that exhibits suspicious nesting patterns. Security teams should also consider deploying runtime protections such as stack canaries or address space layout randomization to reduce the exploitability of such memory corruption vulnerabilities. The implementation of automated testing for CSS parsing functions and regular security audits of third-party libraries will help prevent similar issues from emerging in future software deployments.