CVE-2015-8387 in PCRE
Summary
by MITRE
PCRE before 8.38 mishandles (?123) subroutine calls and related subroutine calls, 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-2015-8387 affects PCRE (Perl Compatible Regular Expressions) versions prior to 8.38 and represents a critical security flaw in regular expression processing. This vulnerability specifically targets the handling of subroutine calls within regular expressions, particularly those beginning with (?123) patterns that reference subroutine calls. The flaw exists in the parsing and execution logic of the PCRE library when processing certain malformed regular expressions, creating a scenario where malicious inputs can trigger unexpected behavior in applications relying on PCRE for pattern matching operations.
The technical implementation of this vulnerability stems from improper integer handling during the parsing phase of subroutine calls in regular expressions. When the PCRE library encounters a subroutine reference such as (?123), it attempts to process this as a valid subroutine call but fails to properly validate the integer values used in the reference. This leads to an integer overflow condition that can cause the library to behave unpredictably, potentially resulting in memory corruption or application crashes. The 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 CVE-2015-8387 extends beyond simple denial of service scenarios, as the integer overflow condition can potentially lead to more severe consequences including arbitrary code execution or information disclosure. Attackers can craft malicious regular expressions that, when processed by vulnerable PCRE implementations, will cause the application to enter an unstable state. This vulnerability affects a wide range of applications and systems that utilize PCRE for regular expression processing, including web browsers, web application firewalls, intrusion detection systems, and various server-side applications. The exploitation of this vulnerability through JavaScript RegExp objects in Konqueror demonstrates the real-world impact on web browsers and highlights the potential for widespread exploitation in web environments where regular expressions are extensively used for input validation.
The vulnerability aligns with CWE-190, Integer Overflow or Wraparound, which describes situations where integer arithmetic operations produce results that exceed the maximum value representable by the data type. This flaw also maps to ATT&CK technique T1059.007, Command and Scripting Interpreter: JavaScript, as it specifically targets JavaScript RegExp processing and can be exploited through web-based JavaScript execution. Additionally, the vulnerability demonstrates characteristics of T1499.004, Network Denial of Service, as it can cause service disruption through controlled resource exhaustion. Organizations using PCRE-based systems should prioritize immediate patching of affected versions to prevent exploitation, as the vulnerability can be leveraged for both denial of service attacks and potentially more sophisticated exploitation techniques that could compromise system integrity and availability.
This vulnerability serves as a reminder of the critical importance of proper input validation and integer overflow protection in security-critical libraries. The impact of such flaws extends far beyond individual applications, affecting entire ecosystems where PCRE is utilized for security purposes. The remediation approach requires updating to PCRE version 8.38 or later, which includes proper bounds checking and integer overflow protection mechanisms. System administrators and security teams should conduct comprehensive vulnerability assessments to identify all systems and applications that may be vulnerable to this issue, particularly those that process untrusted regular expression inputs or rely on PCRE for security-related functions. The vulnerability also underscores the need for thorough security testing of regular expression processing capabilities and the importance of implementing robust error handling mechanisms to prevent exploitation of similar integer overflow conditions in other libraries and applications.