CVE-2007-2026 in file
Summary
by MITRE
The gnu regular expression code in file 4.20 allows context-dependent attackers to cause a denial of service (CPU consumption) via a crafted document with a large number of line feed characters, which is not well handled by OS/2 REXX regular expressions that use wildcards, as originally reported for AMaViS.
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Analysis
by VulDB Data Team • 07/18/2019
The vulnerability identified as CVE-2007-2026 represents a significant denial of service weakness within the GNU regular expression implementation, specifically affecting version 4.20 of the library. This flaw manifests when processing documents containing an excessive number of line feed characters, creating a scenario where the regular expression engine becomes overwhelmed by the pattern matching operations required to handle such inputs. The vulnerability was originally discovered and reported within the context of AMaViS, a mail filtering system that relies heavily on regular expression processing for content analysis and filtering operations. The issue stems from the inefficient handling of wildcard patterns in OS/2 REXX regular expressions, which are utilized by the GNU regex library for pattern matching operations.
The technical root cause of this vulnerability lies in the algorithmic inefficiency of the regular expression engine when confronted with pathological input patterns containing numerous consecutive line feed characters. When the regex engine processes such inputs, it enters into a computationally expensive state where the backtracking mechanisms become excessively active, leading to exponential time complexity in pattern matching operations. This behavior creates a condition where CPU resources are consumed at an alarming rate, effectively rendering the system or application unresponsive to legitimate requests. The vulnerability is context-dependent because it requires specific input patterns that trigger the problematic code paths within the regex implementation, making it less straightforward to exploit but still potentially devastating in impact.
The operational impact of CVE-2007-2026 extends beyond simple service disruption, as it can effectively paralyze mail filtering systems and other applications that depend on regular expression processing. In the case of AMaViS, this vulnerability could lead to complete system downtime, preventing legitimate email processing while attackers could potentially use this weakness to launch resource exhaustion attacks against mail servers. The vulnerability's classification aligns with CWE-400, which addresses unchecked resource consumption in software systems, and demonstrates how seemingly benign input handling can become a critical security concern when combined with inefficient algorithms. Organizations using affected systems face the risk of denial of service attacks that can be executed with relatively simple input patterns, making this vulnerability particularly dangerous in networked environments where mail processing systems are commonly targeted.
Mitigation strategies for this vulnerability require both immediate patching and architectural considerations to prevent similar issues in the future. The primary solution involves updating to patched versions of the GNU regex library where the problematic backtracking algorithms have been optimized or replaced with more efficient implementations. System administrators should also implement input validation mechanisms that limit the number of consecutive line feed characters allowed in processed documents, creating a defense-in-depth approach that reduces the attack surface. Additionally, implementing rate limiting and resource monitoring for regular expression processing operations can help detect and prevent exploitation attempts before they cause significant system impact. This vulnerability highlights the importance of considering algorithmic complexity in security design and demonstrates how the NIST Cybersecurity Framework's risk management principles should be applied to software development processes to prevent such issues from arising in the first place.