CVE-2017-16231 in PCRE
Summary
by MITRE
** DISPUTED ** In PCRE 8.41, after compiling, a pcretest load test PoC produces a crash overflow in the function match() in pcre_exec.c because of a self-recursive call. NOTE: third parties dispute the relevance of this report, noting that there are options that can be used to limit the amount of stack that is used.
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Analysis
by VulDB Data Team • 07/04/2024
The vulnerability identified as CVE-2017-16231 relates to a critical stack overflow condition within the Perl Compatible Regular Expressions library version 8.41. This issue manifests during the execution phase of regular expression matching when a specific pattern triggers a self-recursive call within the match() function located in pcre_exec.c. The problem occurs specifically in the context of pcretest load testing scenarios where maliciously crafted regular expressions can cause the application to crash due to excessive stack consumption. The vulnerability represents a classic stack buffer overflow scenario that can potentially lead to arbitrary code execution or denial of service conditions.
From a technical perspective, this vulnerability falls under CWE-121, which describes stack-based buffer overflow conditions, and demonstrates the dangerous nature of recursive regular expression matching algorithms. The self-recursive call pattern in the match() function creates an unbounded recursion chain that consumes stack space rapidly, eventually leading to stack exhaustion and program termination. This type of vulnerability is particularly concerning in regular expression engines because regex patterns can be crafted to exploit the backtracking behavior in ways that amplify the stack consumption exponentially. The attack surface is expanded by the fact that regular expression processing is commonly used in web applications, network security tools, and system utilities where input validation may not adequately restrict pattern complexity.
The operational impact of CVE-2017-16231 extends beyond simple application crashes to potentially compromise system availability and stability. When exploited in web applications or security tools that process untrusted user input through regular expressions, this vulnerability can enable denial of service attacks that render services unavailable to legitimate users. The vulnerability's exploitation requires specific conditions where the input pattern triggers the recursive behavior, but given the widespread use of PCRE in various software components, the potential impact is significant. The issue is particularly relevant in environments where regular expression processing occurs in security-sensitive contexts such as intrusion detection systems, web application firewalls, or log analysis tools that may process user-supplied patterns.
Organizations should consider multiple mitigation strategies to address this vulnerability effectively. The primary recommendation involves upgrading to PCRE versions that have addressed this recursion limit issue, as newer versions implement stack depth limiting mechanisms and improved recursion handling. Additionally, implementing input validation and limiting the complexity of regular expressions processed by applications can significantly reduce exposure. The use of alternative regex engines or libraries that provide better recursion control mechanisms represents another viable approach. Security practitioners should also consider implementing monitoring and alerting for unusual regex processing patterns that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving execution of malicious code through input processing and resource exhaustion attacks, making it relevant to both defensive and offensive security operations. The disputed nature of the report suggests that proper configuration and parameter settings can mitigate the risk, but organizations should not rely solely on these mitigations without proper validation and testing.