CVE-2022-31099 in rulex
Summary
by MITRE • 06/28/2022
rulex is a new, portable, regular expression language. When parsing untrusted rulex expressions, the stack may overflow, possibly enabling a Denial of Service attack. This happens when parsing an expression with several hundred levels of nesting, causing the process to abort immediately. This is a security concern for you, if your service parses untrusted rulex expressions (expressions provided by an untrusted user), and your service becomes unavailable when the process running rulex aborts due to a stack overflow. The crash is fixed in version **0.4.3**. Affected users are advised to update to this version. There are no known workarounds for this issue.
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Analysis
by VulDB Data Team • 07/16/2022
CVE-2022-31099 represents a stack overflow vulnerability in rulex, a portable regular expression language designed for cross-platform compatibility. This vulnerability stems from insufficient input validation during the parsing of rulex expressions, specifically when handling deeply nested structures that exceed several hundred levels of nesting. The flaw manifests as an uncontrolled stack growth condition that ultimately leads to process termination through stack overflow. The vulnerability is classified as a classic stack-based buffer overflow, which falls under the CWE-772 category of "Missing Release of Resource after Effective Lifetime" and more specifically aligns with CWE-121 for "Stack-based Buffer Overflow". The security implications extend beyond simple denial of service as this vulnerability can be exploited by malicious actors to disrupt service availability, making it particularly concerning for applications that process untrusted user input.
The technical exploitation of this vulnerability occurs during the parsing phase of rulex expressions where the recursive parsing algorithm fails to implement proper depth limiting mechanisms. When an attacker submits a crafted rulex expression containing excessive nesting levels, the parser's call stack grows exponentially until it exceeds the system's stack limit, causing immediate process termination. This behavior demonstrates a fundamental lack of input sanitization and resource management controls within the rulex parser implementation. The vulnerability's impact is amplified because rulex is designed to be embedded in various applications, meaning any service that accepts user-provided rulex expressions becomes a potential target. The crash occurs at the process level rather than being recoverable through normal error handling, making it particularly disruptive to service availability. According to ATT&CK framework, this vulnerability maps to T1499.004 "Endpoint Denial of Service" and potentially T1595.001 "Network Denial of Service" when considering the broader impact on networked services.
The operational impact of CVE-2022-31099 extends beyond immediate service disruption to encompass potential business continuity issues and reputational damage. Organizations relying on rulex for pattern matching, filtering, or validation tasks face significant risk when processing untrusted input from external sources. The vulnerability affects any application that integrates rulex and processes user-provided expressions without proper input validation, creating a wide attack surface across various deployment scenarios. Service providers using rulex in web applications, network security tools, or data processing pipelines are particularly vulnerable as these systems often encounter untrusted input from multiple sources. The fix implemented in version 0.4.3 addresses the core issue by introducing proper stack depth limiting and recursive parsing controls. Organizations must prioritize updating their rulex implementations to version 0.4.3 or later to remediate this vulnerability, as no effective workarounds exist for preventing the stack overflow condition. The vulnerability's severity classification as a denial of service issue underscores the importance of maintaining up-to-date security patches in production environments. Without proper mitigation, systems remain susceptible to intentional exploitation that could lead to extended service outages and potential revenue loss. Security teams should implement monitoring for rulex-related parsing activities and establish incident response procedures to address potential exploitation attempts. The vulnerability highlights the critical need for input validation and resource management controls in parsing libraries, particularly those handling recursive data structures.