CVE-2015-8381 in PCRE
Summary
by MITRE
The compile_regex function in pcre_compile.c in PCRE before 8.38 and pcre2_compile.c in PCRE2 before 10.2x mishandles the /(?J:(?|(:(?|(?'R')(\k'R')|((?'R')))H'Rk'Rf)|s(?'R'))))/ and /(?J:(?|(:(?|(?'R')(\z(?|(?'R')(\k'R')|((?'R')))k'R')|((?'R')))H'Ak'Rf)|s(?'R')))/ patterns, and related patterns with certain group references, which allows remote attackers to cause a denial of service (heap-based buffer overflow) or possibly have unspecified other impact via a crafted regular expression, as demonstrated by a JavaScript RegExp object encountered by Konqueror.
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Analysis
by VulDB Data Team • 06/28/2022
The vulnerability described in CVE-2015-8381 represents a critical heap-based buffer overflow in the PCRE (Perl Compatible Regular Expressions) library affecting versions prior to 8.38 and PCRE2 versions before 10.2x. This flaw exists within the compile_regex function in pcre_compile.c and pcre2_compile.c, where the library fails to properly handle specific complex regular expression patterns containing nested group references and conditional constructs. The affected patterns utilize the (?J:) syntax for duplicate named group support combined with nested conditional constructs (?|) and recursive group references (\k'R') that create a scenario where the parser's internal memory management becomes corrupted during compilation. The vulnerability specifically manifests when processing regular expressions that contain recursive references to named groups within conditional constructs, creating a situation where the library allocates insufficient memory for internal structures while simultaneously attempting to write beyond allocated boundaries.
The technical exploitation of this vulnerability occurs through carefully crafted regular expressions that leverage the interaction between named group references, conditional matching constructs, and recursive pattern matching. When the PCRE library processes these malformed patterns, it enters a state where it attempts to allocate memory for internal tracking structures but fails to account for the recursive nature of the pattern matching, leading to heap corruption. The attack vector is particularly insidious because it can be triggered through JavaScript RegExp objects processed by web browsers like Konqueror, making it exploitable in web-based environments where regular expressions are commonly used for input validation and pattern matching. The flaw is categorized under CWE-121 as a heap-based buffer overflow, which represents a classic memory safety issue where insufficient bounds checking allows arbitrary writes to heap memory locations.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable more sophisticated attacks depending on the execution environment. Remote attackers can cause applications using vulnerable PCRE libraries to crash through heap corruption, leading to denial of service conditions that can disrupt legitimate service operations. In some cases, the memory corruption could potentially be leveraged for more severe consequences including arbitrary code execution, though the specific exploitability depends on the target environment's memory protection mechanisms. The vulnerability affects a wide range of applications that rely on PCRE for regular expression processing, including web servers, email servers, intrusion detection systems, and various scripting environments that utilize regular expressions for input validation and pattern matching. The attack is particularly concerning in web environments where user input is processed through regular expressions, as it can be triggered through maliciously crafted input that gets processed by vulnerable applications.
Mitigation strategies for CVE-2015-8381 require immediate patching of all affected PCRE and PCRE2 installations to versions 8.38 or later for PCRE and 10.2x or later for PCRE2, which contain the necessary fixes for proper memory management during regular expression compilation. Organizations should also implement input validation measures to prevent untrusted regular expressions from being processed by applications, including limiting the complexity of regular expressions that can be submitted by users. Additionally, implementing proper bounds checking and memory protection mechanisms in applications that utilize PCRE libraries can help reduce the impact of potential exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1059.007 for the execution of malicious code through regular expression processing, and T1499.004 for denial of service attacks targeting application memory corruption. Organizations should also consider implementing network segmentation and monitoring for unusual regular expression processing patterns that might indicate exploitation attempts, particularly in web applications that process user input through regular expression engines.