CVE-2015-8380 in PCRE
Summary
by MITRE
The pcre_exec function in pcre_exec.c in PCRE before 8.38 mishandles a // pattern with a \01 string, which allows remote attackers to cause a denial of service (heap-based buffer 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-2015-8380 represents a critical heap-based buffer overflow in the PCRE (Perl Compatible Regular Expressions) library version 8.37 and earlier. This flaw exists within the pcre_exec function located in pcre_exec.c, specifically when processing certain malformed regular expression patterns that contain a forward slash followed by a null byte character. The issue manifests when the library encounters a pattern such as // followed by a null character, which triggers improper memory handling during the regular expression execution process. The vulnerability was particularly concerning because it could be exploited through JavaScript RegExp objects processed by web browsers, making it applicable to web-based attack scenarios where regular expressions are commonly used for input validation and pattern matching.
The technical root cause of this vulnerability stems from inadequate bounds checking within the pcre_exec function's handling of specific pattern combinations. When the regular expression engine processes the malformed // pattern with a null byte, it fails to properly validate memory allocation and buffer boundaries, leading to a situation where memory operations exceed allocated buffer limits. This improper memory management creates a heap-based buffer overflow condition that can be exploited by remote attackers to either crash the application through denial of service or potentially execute arbitrary code depending on the system configuration and memory layout. The vulnerability is classified under CWE-121 as a heap-based buffer overflow, which occurs when more data is written to a buffer than it can hold, and it aligns with ATT&CK technique T1059.007 for script-based execution through web applications.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it represents a potential path for remote code execution in affected systems. Web browsers that utilize PCRE for JavaScript regular expression processing, including Konqueror mentioned in the original description, become vulnerable to attacks that could compromise user sessions or system integrity. The exploitability of this vulnerability is enhanced by its ability to be triggered through common web-based inputs such as JavaScript RegExp objects, making it particularly dangerous in web applications where user input is processed through regular expression engines. Attackers could craft malicious regular expressions that, when processed by vulnerable applications, would cause heap corruption and potentially lead to arbitrary code execution or system crashes, affecting both client-side and server-side applications that depend on PCRE for pattern matching operations.
Mitigation strategies for CVE-2015-8380 require immediate patching of all affected PCRE installations to version 8.38 or later, where the buffer overflow handling has been corrected. Organizations should also implement input validation and sanitization measures to prevent malformed regular expressions from reaching the PCRE engine, particularly in web applications that process user-supplied data. Additionally, system administrators should consider implementing application-level restrictions on regular expression complexity and length to reduce the attack surface. The fix implemented in PCRE 8.38 addresses the specific memory handling issue by adding proper bounds checking and validation for the pattern processing logic, preventing the heap overflow condition that previously occurred when encountering the // pattern with null byte sequences. Security monitoring should include detection of suspicious regular expression patterns that could trigger similar buffer overflow conditions in other regular expression libraries or components within the application stack.