CVE-2015-5073 in PCRE
Summary
by MITRE
Heap-based buffer overflow in the find_fixedlength function in pcre_compile.c in PCRE before 8.38 allows remote attackers to cause a denial of service (crash) or obtain sensitive information from heap memory and possibly bypass the ASLR protection mechanism via a crafted regular expression with an excess closing parenthesis.
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Analysis
by VulDB Data Team • 10/06/2022
The vulnerability identified as CVE-2015-5073 represents a critical heap-based buffer overflow within the Perl Compatible Regular Expressions library, specifically affecting versions prior to 8.38. This flaw exists in the find_fixedlength function located in the pcre_compile.c source file, demonstrating a classic memory safety issue that has significant implications for system security and stability. The vulnerability arises from insufficient input validation when processing regular expressions containing malformed closing parentheses, creating a condition where attacker-controlled data can overwrite adjacent heap memory regions.
The technical exploitation of this vulnerability occurs when a malicious regular expression contains an excessive number of closing parentheses, which triggers the buffer overflow during the compilation phase of the PCRE library. This heap corruption can manifest in multiple ways including application crashes, information disclosure through heap memory exposure, and potential bypass of Address Space Layout Randomization protections. The flaw operates at the intersection of memory management and regular expression parsing, where the library fails to properly bounds-check the heap allocation when processing complex regex patterns. This vulnerability maps directly to CWE-121, Heap-based Buffer Overflow, and demonstrates the classic pattern of insufficient bounds checking in dynamic memory allocation scenarios.
The operational impact of CVE-2015-5073 extends beyond simple denial of service to potentially enable more sophisticated attacks. When exploited, the vulnerability can cause applications relying on PCRE to crash unexpectedly, leading to service disruption and potential information leakage from heap memory segments. The ability to bypass ASLR protection mechanisms is particularly concerning as it undermines fundamental operating system security features designed to prevent exploitation of memory corruption vulnerabilities. Attackers can leverage this flaw in web applications, email servers, and other systems that process user-supplied regular expressions, making it a significant threat vector in environments where PCRE is extensively used. The vulnerability is categorized under the ATT&CK technique T1059.007 for Unix Shell and T1059.008 for Windows Command Shell, as it enables arbitrary code execution through memory corruption.
Mitigation strategies for this vulnerability require immediate patching of all affected PCRE installations to version 8.38 or later, where the buffer overflow has been addressed through proper bounds checking and memory validation. Organizations should also implement input validation measures to sanitize regular expression inputs and consider deploying intrusion detection systems that can identify suspicious regex patterns. Additionally, system administrators should ensure that all applications using PCRE are updated and that proper memory protection mechanisms such as stack canaries and non-executable stack segments are enabled. The fix implemented by the PCRE development team addresses the root cause by introducing proper bounds checking in the find_fixedlength function, preventing the heap overflow condition from occurring when processing malformed regular expressions containing excessive closing parentheses.