CVE-2006-7227 in PCRE
Summary
by MITRE
Integer overflow in Perl-Compatible Regular Expression (PCRE) library before 6.7 allows context-dependent attackers to execute arbitrary code via a regular expression containing a large number of named subpatterns (name_count) or long subpattern names (max_name_size), which triggers a buffer overflow. NOTE: this issue was originally subsumed by CVE-2006-7224, but that CVE has been REJECTED and split.
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Analysis
by VulDB Data Team • 07/29/2021
The vulnerability described in CVE-2006-7227 represents a critical integer overflow condition within the Perl-Compatible Regular Expression library version 6.6 and earlier. This flaw exists in the parsing mechanism of regular expressions and specifically targets the handling of named subpatterns within PCRE implementations. The vulnerability manifests when processing regular expressions containing either an excessive number of named subpatterns or subpattern names that exceed normal length parameters, creating conditions where integer arithmetic operations overflow and result in buffer corruption. The issue stems from inadequate input validation and boundary checking within the library's internal data structures that manage named pattern information.
The technical exploitation of this vulnerability occurs through carefully crafted regular expressions that manipulate the name_count parameter and max_name_size variables within the PCRE parsing engine. When the library processes these malformed expressions, the integer overflow causes memory allocation calculations to produce incorrect buffer sizes, leading to buffer overflow conditions that can be leveraged by attackers to execute arbitrary code. The vulnerability is context-dependent, meaning that successful exploitation requires specific conditions related to how the regular expression is processed and the exact values used in the malicious pattern construction. The underlying flaw falls under CWE-190, Integer Overflow or Wraparound, which is classified as a fundamental weakness in software arithmetic operations that can lead to memory corruption vulnerabilities.
From an operational perspective, this vulnerability poses significant risks to systems that rely on PCRE for regular expression processing, particularly in web applications, network security tools, and any software that accepts user-supplied regular expressions. Attackers can exploit this weakness by crafting malicious regular expressions that, when processed by vulnerable systems, trigger the buffer overflow condition and potentially allow remote code execution. The impact extends across multiple platforms and applications that depend on PCRE, including but not limited to web servers, intrusion detection systems, and security scanning tools that utilize regular expression matching. The vulnerability's classification under ATT&CK technique T1059.007 for Command and Scripting Interpreter indicates its potential for enabling malicious command execution through regular expression processing.
The primary mitigation strategy involves upgrading to PCRE version 6.7 or later, where the integer overflow conditions have been addressed through proper input validation and boundary checking mechanisms. System administrators should also implement regular expression validation and sanitization measures to prevent untrusted input from reaching the PCRE processing engine. Additional protective measures include deploying input filtering at network boundaries, implementing application-level restrictions on regular expression complexity, and monitoring for suspicious pattern matching activities. Organizations should also consider using alternative regular expression libraries that have been audited for similar vulnerabilities and maintain comprehensive patch management processes to ensure timely deployment of security updates across all affected systems. The vulnerability demonstrates the critical importance of proper integer arithmetic handling in security-sensitive code and the potential for seemingly benign input processing operations to become attack vectors when proper bounds checking is absent.