CVE-2015-2325 in PCRE
Summary
by MITRE
The compile_branch function in PCRE before 8.37 allows context-dependent attackers to compile incorrect code, cause a denial of service (out-of-bounds heap read and crash), or possibly have other unspecified impact via a regular expression with a group containing a forward reference repeated a large number of times within a repeated outer group that has a zero minimum quantifier.
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Analysis
by VulDB Data Team • 04/27/2025
The vulnerability identified as CVE-2015-2325 affects the Perl Compatible Regular Expressions library version 8.36 and earlier, specifically targeting the compile_branch function within the PCRE engine. This flaw represents a critical security issue that demonstrates how improper handling of regular expression parsing can lead to severe system instability and potential exploitation. The vulnerability is classified under CWE-129 as an Improper Validation of Array Index, which directly relates to the out-of-bounds heap read condition that occurs during the compilation process. The issue manifests when processing regular expressions containing forward references within nested quantified groups, creating a scenario where the parser fails to properly validate memory access patterns during code generation.
The technical exploitation of this vulnerability occurs when a regular expression contains a group with a forward reference that is repeated a large number of times within an outer group that has a zero minimum quantifier. During the compilation phase, the compile_branch function attempts to process these complex nested structures without adequate bounds checking, leading to memory corruption. The heap read operations extend beyond allocated memory boundaries, causing the application to crash or potentially allowing for further exploitation. This behavior aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter: Python, though the specific vector is through regular expression processing rather than direct scripting execution. The vulnerability demonstrates how regular expression engines can become attack surfaces when they fail to properly validate complex pattern structures.
The operational impact of this vulnerability extends beyond simple denial of service, as it can potentially allow for more sophisticated attacks depending on the environment where PCRE is utilized. Applications that process untrusted regular expressions, including web applications, network security tools, and system utilities, become vulnerable to this class of attack. The vulnerability is particularly concerning because it can be triggered through user input that gets processed as regular expressions, making it applicable to a wide range of software systems. When exploited, the out-of-bounds memory access can cause unpredictable behavior including crashes, data corruption, or in some scenarios, arbitrary code execution depending on the specific implementation and memory layout. This type of vulnerability directly impacts the reliability and security posture of systems relying on PCRE for text processing and pattern matching operations.
Mitigation strategies for CVE-2015-2325 focus primarily on upgrading to PCRE version 8.37 or later, where the vulnerability has been addressed through improved bounds checking in the compile_branch function. Organizations should also implement input validation measures to limit the complexity and length of regular expressions processed by applications, particularly those accepting user input. The fix implemented by the PCRE maintainers includes enhanced validation of forward references within repeated groups and proper bounds checking during compilation. Additionally, system administrators should monitor applications that utilize PCRE for regular expression processing and ensure that all components are updated to versions that contain the necessary security patches. The vulnerability highlights the importance of regular security updates and proper input sanitization, particularly in systems that process untrusted data through pattern matching mechanisms. Organizations should also consider implementing rate limiting and complexity checks on regular expression processing to prevent exploitation of similar vulnerabilities in other parts of their software stack.