CVE-2015-2328 in PCRE
Summary
by MITRE
PCRE before 8.36 mishandles the /((?(R)a|(?1)))+/ pattern and related patterns with certain recursion, which allows remote attackers to cause a denial of service (segmentation fault) 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-2015-2328 represents a critical flaw in the Perl Compatible Regular Expressions library version 8.35 and earlier, which can be exploited to cause denial of service or potentially more severe impacts through crafted regular expressions. This issue specifically affects the handling of recursive patterns within PCRE, creating a scenario where malicious inputs can trigger unexpected behavior in applications that rely on regular expression processing. The vulnerability manifests when processing the pattern "/((?(R)a|(?1)))+/" and similar recursive constructs, which are commonly encountered in web browsers and JavaScript engines when processing regular expressions through RegExp objects. The flaw resides in the library's recursive pattern matching algorithm, where improper handling of recursion leads to memory corruption or stack exhaustion.
The technical implementation of this vulnerability stems from the way PCRE processes recursive patterns during compilation and execution phases. When encountering recursive constructs like "(?1)" which refers to the first subpattern, the library fails to properly manage the recursion depth and stack allocation. This particular pattern structure creates a scenario where the recursive matching engine enters an infinite loop or encounters memory management issues that result in segmentation faults. The vulnerability is particularly dangerous because it can be triggered through user-controllable input, such as JavaScript regular expressions processed by web browsers like Konqueror. The flaw demonstrates characteristics consistent with CWE-121, heap-based buffer overflow, and CWE-122, stack-based buffer overflow, as the memory corruption occurs during pattern processing operations.
The operational impact of this vulnerability extends beyond simple denial of service, as it can potentially enable more sophisticated attacks depending on the execution environment. Remote attackers can craft malicious regular expressions that, when processed by vulnerable applications, cause segmentation faults leading to application crashes and system instability. In web browser contexts, this vulnerability can be exploited to crash browser processes or potentially execute arbitrary code through memory corruption, especially when combined with other exploitation techniques. The vulnerability affects web applications that process user input through regular expression engines, including web browsers, web application firewalls, and server-side applications using PCRE for input validation. The impact is particularly severe in environments where regular expressions are frequently used for input sanitization, as a single malicious input can compromise the entire application or system.
Mitigation strategies for CVE-2015-2328 primarily focus on upgrading to PCRE version 8.36 or later, which includes fixes for the recursive pattern handling issue. System administrators should prioritize patching affected applications and libraries that depend on vulnerable PCRE versions, particularly web browsers and server applications. Additional protective measures include implementing regular expression input validation, limiting the complexity and length of regular expressions processed by applications, and using alternative regular expression engines that have been verified as free from similar issues. Organizations should also consider implementing web application firewalls that can detect and block malicious regular expression patterns, as well as monitoring for unusual patterns of resource consumption that may indicate exploitation attempts. The vulnerability's exploitation aligns with ATT&CK technique T1059.007 for command and scripting interpreter, specifically targeting JavaScript engines through regular expression processing, making it particularly relevant for organizations implementing security monitoring and incident response procedures.