CVE-2017-6004 in PCRE
Summary
by MITRE
The compile_bracket_matchingpath function in pcre_jit_compile.c in PCRE through 8.x before revision 1680 (e.g., the PHP 7.1.1 bundled version) allows remote attackers to cause a denial of service (out-of-bounds read and application crash) via a crafted regular expression.
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Analysis
by VulDB Data Team • 12/27/2024
The vulnerability identified as CVE-2017-6004 represents a critical out-of-bounds read condition within the PCRE (Perl Compatible Regular Expressions) library's Just-In-Time compilation functionality. This flaw exists in the compile_bracket_matchingpath function located in pcre_jit_compile.c, affecting PCRE versions through 8.x before revision 1680. The vulnerability specifically impacts the PHP 7.1.1 bundled version of PCRE, making it particularly relevant for web applications that rely on regular expression processing for input validation, data parsing, or pattern matching operations. The issue stems from inadequate bounds checking during the JIT compilation phase of regular expression processing, creating a scenario where maliciously crafted regular expressions can trigger memory access violations.
The technical implementation of this vulnerability involves the improper handling of bracket expressions within the JIT compilation path of PCRE's regular expression engine. When a crafted regular expression containing specific bracket patterns is processed through the compile_bracket_matchingpath function, the JIT compiler fails to properly validate array indices or memory boundaries during the compilation process. This results in an out-of-bounds memory read operation that can access memory locations outside the intended data structures, ultimately leading to application crashes or unpredictable behavior. The vulnerability is classified under CWE-125 as an out-of-bounds read, which represents an insufficient boundary check in memory access operations. The flaw demonstrates characteristics consistent with memory safety issues that can be exploited by attackers to cause denial of service conditions or potentially escalate to more severe security impacts depending on the execution environment.
The operational impact of CVE-2017-6004 extends beyond simple denial of service, as it can affect the stability and availability of applications that depend on PCRE for regular expression processing. Web applications, particularly those written in PHP, are at significant risk since they often utilize regular expressions for input validation, data filtering, and pattern matching operations. When exploited, this vulnerability can cause complete application crashes, forcing administrators to restart services and potentially disrupting user access. The attack vector requires only the submission of a specially crafted regular expression, making it particularly dangerous in environments where user input is processed through regular expression engines. From an attack framework perspective, this vulnerability aligns with techniques described in the ATT&CK matrix under T1059.007 for Command and Scripting Interpreter, where the exploitation involves manipulating regular expression parsing to cause system instability. The vulnerability is especially concerning in web applications because it can be triggered through common input validation scenarios, making it difficult to detect and prevent through standard security measures.
Mitigation strategies for CVE-2017-6004 primarily involve upgrading to PCRE versions 8.x with revision 1680 or later, which contain the necessary patches to address the out-of-bounds read condition. System administrators should prioritize updating their PHP installations and underlying PCRE libraries to ensure protection against this vulnerability. Additionally, implementing proper input validation and sanitization practices can help reduce the risk of exploitation by limiting the types of regular expressions that reach the vulnerable JIT compilation path. Organizations should also consider implementing monitoring and logging mechanisms to detect unusual patterns of regular expression usage that might indicate attempted exploitation. The vulnerability serves as a reminder of the importance of keeping third-party libraries updated and maintaining comprehensive security patch management processes, particularly for components that handle user input processing and pattern matching operations.