CVE-2015-8394 in PCRE
Summary
by MITRE
PCRE before 8.38 mishandles the (?(<digits>) and (?(R<digits>) conditions, which allows remote attackers to cause a denial of service (integer 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 identified as CVE-2015-8394 affects PCRE (Perl Compatible Regular Expressions) libraries version 8.37 and earlier, representing a critical security flaw that can be exploited to cause denial of service or potentially more severe impacts through crafted regular expressions. This vulnerability specifically targets the handling of conditional constructs within regular expressions, namely the (?(<digits>) and (?(R<digits>) syntax patterns that are used to create conditional matching logic in regular expression engines.
The technical flaw manifests in how PCRE processes these conditional expressions when they contain digit sequences, leading to improper integer overflow conditions during the parsing and compilation phases of regular expression evaluation. When a malicious user crafts a regular expression containing these specific conditional patterns with numeric values, the library fails to properly validate the input parameters, resulting in integer overflow conditions that can cause the application to crash or behave unpredictably. This vulnerability is particularly dangerous 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 operational impact of this vulnerability extends beyond simple denial of service scenarios, as the integer overflow conditions could potentially lead to unspecified other impacts that might include arbitrary code execution or information disclosure depending on the specific implementation and context in which the vulnerable library is used. The vulnerability affects web browsers, web applications, and any software that relies on PCRE for regular expression processing, creating a wide attack surface that could be exploited by remote attackers. When exploited, this vulnerability can cause applications to crash or become unresponsive, effectively preventing legitimate users from accessing services, while the potential for more severe impacts makes it particularly concerning for security professionals managing web applications and browser-based systems.
The vulnerability maps to CWE-190, Integer Overflow or Wraparound, which specifically addresses issues where integer arithmetic operations produce results that exceed the maximum value that can be represented by the data type, and it aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter: JavaScript, as the exploitation occurs through JavaScript RegExp objects. Organizations should implement immediate mitigations including upgrading to PCRE version 8.38 or later, which contains the necessary patches to properly handle these conditional expressions without causing integer overflow conditions. Additionally, input validation should be strengthened to prevent malicious regular expressions from being processed, and runtime protections such as sandboxing or memory protection mechanisms should be considered to limit the potential impact of successful exploitation attempts.