CVE-2015-8382 in PCRE
Summary
by MITRE
The match function in pcre_exec.c in PCRE before 8.37 mishandles the /(?:((abcd))|(((?:(?:(?:(?:abc|(?:abcdef))))b)abcdefghi)abc)|((*ACCEPT)))/ pattern and related patterns involving (*ACCEPT), which allows remote attackers to obtain sensitive information from process memory or cause a denial of service (partially initialized memory and application crash) via a crafted regular expression, as demonstrated by a JavaScript RegExp object encountered by Konqueror, aka ZDI-CAN-2547.
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Analysis
by VulDB Data Team • 06/28/2022
The vulnerability identified as CVE-2015-8382 represents a critical flaw in the Perl Compatible Regular Expressions library, specifically within the pcre_exec.c module of PCRE versions prior to 8.37. This security issue stems from improper handling of certain complex regular expression patterns that include the (ACCEPT) verb, which is designed to immediately terminate pattern matching and return success. The flaw manifests when processing patterns containing nested capturing groups, conditional constructs, and the (ACCEPT) mechanism in combination with backtracking algorithms, creating a scenario where memory access becomes unpredictable and potentially exploitable.
The technical exploitation of this vulnerability occurs through carefully crafted regular expressions that trigger memory corruption during pattern matching operations. When the pcre_exec function processes the specific pattern structure mentioned in the CVE description, it fails to properly initialize memory structures within the matching engine, leading to information disclosure through partially initialized memory access or application crashes due to improper memory handling. The vulnerability affects web browsers and applications that utilize PCRE for regular expression processing, with Konqueror serving as a demonstrated attack vector through JavaScript RegExp objects. This represents a classic case of buffer over-read and memory corruption that can be leveraged for information disclosure or denial of service attacks.
The operational impact of CVE-2015-8382 extends beyond simple application instability, as it provides attackers with potential access to sensitive process memory that may contain cryptographic keys, user credentials, or other confidential information. The vulnerability's classification aligns with CWE-125, which describes "Out-of-bounds Read" conditions where programs access memory locations beyond the intended boundaries. Additionally, the flaw demonstrates characteristics consistent with CWE-129, "Improper Validation of Array Index," as the memory access patterns become invalid due to improper handling of nested group structures. The attack vector through JavaScript RegExp objects places this vulnerability in the ATT&CK framework under T1059.007 for Command and Scripting Interpreter: JavaScript, and potentially T1068 for Exploitation for Privilege Escalation when combined with other attack vectors.
Mitigation strategies for CVE-2015-8382 primarily involve upgrading to PCRE version 8.37 or later, which includes patches addressing the memory handling issues in the pcre_exec.c module. Organizations should also implement regular expression validation and sanitization practices, particularly when processing untrusted input through regular expression engines. The fix implemented by PCRE developers specifically addresses the handling of (*ACCEPT) verbs within complex nested patterns and ensures proper memory initialization during pattern matching operations. Security teams should monitor for applications that may be using vulnerable versions of PCRE, especially in web browsers, web application frameworks, and server-side applications that rely on regular expression processing for input validation or text processing tasks.