CVE-2011-3661 in Firefox
Summary
by MITRE
YARR, as used in Mozilla Firefox 4.x through 8.0, Thunderbird 5.0 through 8.0, and SeaMonkey before 2.6, allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via crafted JavaScript.
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Analysis
by VulDB Data Team • 03/20/2021
The vulnerability identified as CVE-2011-3661 represents a critical security flaw within the YARR (Yet Another Regular Expression) engine implementation in Mozilla's browser and email client software. This vulnerability affects multiple versions of Firefox, Thunderbird, and SeaMonkey, specifically targeting the JavaScript engine's handling of regular expressions. The issue stems from improper memory management and validation within the YARR engine, which processes regular expression patterns used in JavaScript applications. Attackers can exploit this weakness by crafting malicious JavaScript code containing specially designed regular expressions that trigger memory corruption or unexpected behavior in the application's execution environment.
The technical nature of this vulnerability places it firmly within the category of memory safety issues, specifically related to buffer overflows and memory corruption that can lead to arbitrary code execution. The flaw manifests when the YARR engine processes malformed regular expression patterns, causing it to access memory locations outside the intended boundaries. This type of vulnerability is classified under CWE-125 as "Out-of-bounds Read" and may also relate to CWE-787 "Out-of-bounds Write" depending on the specific exploitation vector. The vulnerability operates at the intersection of JavaScript interpretation and low-level memory management, where the regular expression engine fails to properly validate input parameters before processing them, creating opportunities for attackers to manipulate memory contents.
From an operational perspective, this vulnerability presents significant risk to users of affected software versions, as it can be exploited through web pages or email content without requiring user interaction beyond normal browsing or email reading activities. The exploit potential spans across multiple Mozilla products, making it particularly dangerous as attackers can target users across different application contexts. The vulnerability can result in either denial of service through application crashes or more severe arbitrary code execution, depending on the specific conditions and exploitation techniques employed. This dual nature makes it particularly concerning for enterprise environments where users may encounter malicious content through various channels including phishing emails, compromised websites, or malicious advertisements. The ATT&CK framework categorizes this vulnerability under T1059.007 for "Command and Scripting Interpreter: JavaScript" and potentially T1203 for "Exploitation for Client Execution" when considering the exploitation methodology.
The impact of this vulnerability extends beyond simple application instability, as successful exploitation can provide attackers with complete control over affected systems. The memory corruption issues can be leveraged to execute malicious code with the privileges of the compromised application, potentially leading to full system compromise. Mitigation strategies should include immediate updates to patched versions of affected software, as Mozilla released security updates addressing this specific vulnerability. Organizations should also implement network-based protections such as web application firewalls and content filtering solutions that can detect and block malicious JavaScript patterns. Additionally, user education regarding safe browsing practices and email handling remains crucial, though the automated nature of exploitation makes this approach less reliable as a primary defense mechanism. The vulnerability highlights the importance of regular security updates and the critical need for proper input validation in security-critical components such as regular expression engines.