CVE-2015-8390 in PCRE
Summary
by MITRE
PCRE before 8.38 mishandles the [: and \\ substrings in character classes, which allows remote attackers to cause a denial of service (uninitialized memory read) 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-2015-8390 affects PCRE (Perl Compatible Regular Expressions) versions prior to 8.38 and represents a critical flaw in how the library processes character classes containing specific substring patterns. This issue manifests when the PCRE engine encounters the [: and \ substrings within character class definitions, creating a scenario where uninitialized memory is accessed during regular expression compilation and execution. The vulnerability specifically impacts web browsers and applications that rely on PCRE for pattern matching operations, with Konqueror serving as a notable example of an affected JavaScript engine that processes RegExp objects through this vulnerable library.
The technical root cause of this vulnerability lies in improper handling of character class parsing within PCRE's regular expression engine. When the parser encounters the [: substring within a character class, it fails to properly initialize memory structures before accessing them, leading to uninitialized memory reads that can result in unpredictable behavior. Similarly, the \ substring pattern within character classes triggers the same memory access issue. This flaw falls under the CWE-457 category of "Use of Uninitialized Variable" and can be classified as a memory safety vulnerability that enables both denial of service conditions and potential information disclosure through uninitialized memory content exposure. The vulnerability is particularly concerning because it can be triggered through user-supplied input in regular expressions, making it exploitable in web applications and browser environments where JavaScript RegExp objects are processed.
The operational impact of CVE-2015-8390 extends beyond simple denial of service conditions to potentially enable more sophisticated attacks. Remote attackers can craft malicious regular expressions that trigger uninitialized memory reads, which may lead to information leakage from the application's memory space, including sensitive data such as stack contents, heap information, or other application state. In browser contexts, this vulnerability can be exploited through malicious web pages that contain specially crafted regular expressions, potentially allowing attackers to gather information about the target system or application state. The vulnerability's exploitation capability aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: JavaScript" and T1211 for "Exploitation for Defense Evasion" as it enables attackers to manipulate application behavior through crafted inputs.
The remediation for this vulnerability requires updating to PCRE version 8.38 or later, where the character class parsing logic has been corrected to properly initialize memory structures before accessing them. System administrators and application developers should prioritize patching affected installations, particularly those running web browsers or applications that utilize PCRE for regular expression processing. Additionally, implementing input validation and sanitization measures can provide defense-in-depth protection against malformed regular expressions. Organizations should also consider monitoring for suspicious regular expression patterns in application logs and implementing proper error handling to prevent exploitation attempts. The vulnerability demonstrates the importance of memory safety in regular expression engines and highlights the need for comprehensive testing of parsing logic in security-critical components, as the flaw could potentially be leveraged for information disclosure attacks under certain conditions.