CVE-2005-2491 in PHP
Summary
by MITRE
Integer overflow in pcre_compile.c in Perl Compatible Regular Expressions (PCRE) before 6.2, as used in multiple products such as Python, Ethereal, and PHP, allows attackers to execute arbitrary code via quantifier values in regular expressions, which leads to a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 07/05/2019
The vulnerability described in CVE-2005-2491 represents a critical integer overflow flaw within the Perl Compatible Regular Expressions library that affected numerous software applications including Python, Ethereal (now Wireshark), and PHP. This issue stems from improper handling of quantifier values in regular expression parsing, creating a condition where attackers can manipulate input to trigger memory corruption. The vulnerability specifically resides in the pcre_compile.c source file, which is responsible for compiling regular expression patterns into executable code structures. When processing certain quantifier expressions, the library fails to properly validate integer values, leading to arithmetic overflow conditions that can result in heap-based buffer overflows.
The technical exploitation of this vulnerability occurs when an attacker crafts malicious regular expressions containing specially formatted quantifiers that cause integer overflow during the compilation phase. The overflow results in incorrect memory allocation calculations, where the system allocates insufficient memory for buffer storage while the actual processing attempts to write beyond allocated boundaries. This heap-based buffer overflow creates opportunities for arbitrary code execution, as attackers can control the memory layout to inject and execute malicious code. The flaw demonstrates a classic software security issue where insufficient input validation and integer overflow protection mechanisms allow attackers to manipulate program execution flow through carefully crafted inputs.
From an operational perspective, this vulnerability impacts a wide range of applications that rely on PCRE for text processing and pattern matching operations. The affected products span across different domains including web application frameworks, network protocol analyzers, and scripting languages, making the potential attack surface extensive. Security practitioners must consider that this vulnerability can be exploited through various attack vectors including web application input fields, network packet analysis tools, and any system processing user-supplied regular expressions. The integer overflow condition typically manifests during regular expression compilation rather than execution, making detection more challenging as the vulnerability may not be immediately apparent during normal system operation. The exploitation requires precise control over the quantifier values to trigger the specific overflow condition that leads to memory corruption.
Mitigation strategies for CVE-2005-2491 primarily focus on updating affected systems to PCRE versions 6.2 or later where the integer overflow protection has been implemented. Organizations should prioritize patch management across all systems utilizing vulnerable PCRE libraries, particularly those handling untrusted input through regular expression processing. Additional protective measures include implementing input validation and sanitization for regular expression patterns, limiting the complexity and length of user-supplied patterns, and employing regular expression engines with better overflow protection mechanisms. Security monitoring should include detection of unusual regular expression processing patterns that might indicate attempted exploitation. The vulnerability aligns with CWE-190, Integer Overflow or Wraparound, and represents a technique commonly associated with the ATT&CK tactic of Execution through code injection. Network segmentation and application whitelisting can provide additional defense-in-depth measures to limit potential exploitation impact.