CVE-2006-4566 in Firefox
Summary
by MITRE
Mozilla Firefox before 1.5.0.7, Thunderbird before 1.5.0.7, and SeaMonkey before 1.0.5 allows remote attackers to cause a denial of service (crash) via a malformed JavaScript regular expression that ends with a backslash in an unterminated character set ("[\\"), which leads to a buffer over-read.
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Analysis
by VulDB Data Team • 01/14/2025
This vulnerability affects Mozilla Firefox versions prior to 1.5.0.7, Thunderbird versions prior to 1.5.0.7, and SeaMonkey versions prior to 1.0.5, representing a critical buffer over-read condition that can be exploited to cause denial of service. The flaw occurs when processing malformed JavaScript regular expressions that contain a backslash character at the end of an unterminated character set, specifically in the pattern "[\". This particular syntax creates a scenario where the JavaScript engine fails to properly handle the boundary conditions of the regular expression parser, leading to memory access violations. The vulnerability stems from inadequate input validation and boundary checking within the regular expression engine implementation, which is classified under CWE-121 as a stack-based buffer overflow or more specifically CWE-125 as an out-of-bounds read. The attack vector is remote and requires no authentication, making it particularly dangerous as it can be triggered through web pages or email content that contains malicious regular expressions. When the vulnerable browser encounters such malformed input, the parser attempts to read memory beyond the allocated buffer boundaries, causing the application to crash and potentially leading to a complete denial of service for the affected user. This type of vulnerability falls under the ATT&CK technique T1203 - Exploitation for Client Execution, where adversaries exploit software vulnerabilities to execute arbitrary code or cause system instability. The impact extends beyond simple crashes as it can be used in conjunction with other techniques to create more sophisticated attacks, particularly in environments where automated browser interactions occur. The vulnerability demonstrates a fundamental weakness in the JavaScript engine's ability to handle edge cases in regular expression parsing, highlighting the importance of robust input sanitization and proper memory management in web browser implementations. Security researchers have noted that such buffer over-read conditions are particularly dangerous because they can potentially be chained with other vulnerabilities to achieve arbitrary code execution, though in this specific case the primary impact remains denial of service. The vulnerability was addressed through patches that improved the regular expression parser's boundary checking mechanisms and enhanced input validation to prevent malformed patterns from causing memory access violations. Organizations should ensure immediate patching of affected versions to mitigate the risk of exploitation, as the vulnerability represents a significant threat to browser security and user experience. The incident underscores the critical importance of thorough testing of edge cases in security-sensitive components and the necessity of maintaining up-to-date software to protect against known vulnerabilities. This particular flaw represents a classic example of how seemingly minor parsing issues in complex software systems can lead to serious security implications, emphasizing the need for comprehensive security testing and validation of all input processing components. The vulnerability serves as a reminder of the critical nature of JavaScript engine security in modern browsers, where even small parsing errors can have significant consequences for system stability and user safety.