CVE-2008-0171 in regex library
Summary
by MITRE
regex/v4/perl_matcher_non_recursive.hpp in the Boost regex library (aka Boost.Regex) in Boost 1.33 and 1.34 allows context-dependent attackers to cause a denial of service (failed assertion and crash) via an invalid regular expression.
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Analysis
by VulDB Data Team • 07/30/2021
The vulnerability identified as CVE-2008-0171 resides within the Boost.Regex library version 1.33 and 1.34, specifically in the perl_matcher_non_recursive.hpp component. This issue represents a denial of service weakness that can be exploited through crafted invalid regular expressions, potentially leading to application crashes and system instability. The vulnerability manifests when the regex matching engine encounters malformed patterns that trigger internal assertion failures, causing the application to terminate unexpectedly.
The technical flaw stems from inadequate input validation within the regular expression matching algorithm. When Boost.Regex processes malformed regular expressions, particularly those containing constructs that violate expected parsing patterns, the perl_matcher_non_recursive.hpp module fails to handle these edge cases gracefully. The implementation lacks proper error recovery mechanisms, causing the system to assert and crash rather than gracefully rejecting the invalid pattern or providing appropriate error messaging. This behavior creates a predictable crash scenario that attackers can exploit systematically.
The operational impact of this vulnerability extends beyond simple service disruption, as it can affect any application that relies on Boost.Regex for pattern matching operations. Systems utilizing this library for text processing, log analysis, input validation, or configuration parsing become susceptible to denial of service attacks. Attackers can craft malicious regular expressions that, when processed by vulnerable applications, cause immediate crashes, potentially leading to system unavailability and service interruption. The context-dependent nature of this vulnerability means that exploitation requires the attacker to have knowledge of the target application's usage patterns and the specific regular expressions it processes.
This vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and relates to the broader category of input validation flaws that can lead to denial of service conditions. From an ATT&CK perspective, this weakness maps to the T1499.004 technique involving network denial of service, as the vulnerability enables attackers to disrupt services through crafted input. The attack surface is particularly concerning because regular expressions are commonly used in security-sensitive applications, making this a potential vector for more sophisticated attacks that could be combined with other exploitation techniques.
Mitigation strategies should focus on immediate patching of the Boost library to versions that address this assertion failure issue. Organizations should implement input validation measures that sanitize regular expressions before processing, including limiting pattern complexity and implementing timeouts for matching operations. Additionally, deploying intrusion detection systems that can identify patterns associated with this specific vulnerability can provide early warning of attempted exploitation. Application developers should consider implementing exception handling around regex operations and establishing fallback mechanisms that prevent complete application crashes. The recommended approach includes upgrading to patched versions of Boost 1.35 or later, where this vulnerability has been resolved through improved error handling and input validation mechanisms.