CVE-2025-8037 in Thunderbird
Summary
by MITRE • 07/23/2025
Setting a nameless cookie with an equals sign in the value shadowed other cookies. Even if the nameless cookie was set over HTTP and the shadowed cookie included the `Secure` attribute. This vulnerability affects Firefox < 141, Firefox ESR < 140.1, Thunderbird < 141, and Thunderbird < 140.1.
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Analysis
by VulDB Data Team • 08/09/2025
This vulnerability represents a critical cookie parsing flaw in Mozilla Firefox and Thunderbird browsers that stems from improper handling of nameless cookies containing equals signs in their values. The technical implementation fails to correctly distinguish between cookie name-value pairs when a cookie lacks an explicit name but contains an equals sign within its value field. This parsing error creates a scenario where a nameless cookie with an equals sign can overwrite or shadow other legitimate cookies, regardless of their security attributes or transport protocols. The flaw specifically manifests when a nameless cookie is set over HTTP and subsequently shadows another cookie that includes the Secure attribute, effectively bypassing security mechanisms designed to protect sensitive session data. This vulnerability impacts the fundamental cookie management system that governs how browsers store and retrieve session information, potentially compromising user authentication states and sensitive data protection.
The operational implications of this vulnerability extend beyond simple cookie overwriting to encompass significant security risks in web application authentication and session management. When a nameless cookie containing an equals sign is processed, the browser's cookie parser incorrectly interprets the cookie structure, allowing the nameless cookie to assume control over cookie storage mechanisms. This behavior creates a potential attack vector where malicious actors could craft nameless cookies with specific value patterns to overwrite legitimate session cookies, even those marked as secure or httponly. The vulnerability particularly affects environments where secure cookies are essential for maintaining user sessions, as the security attributes that should protect these cookies become ineffective against this parsing flaw. The impact is amplified because the vulnerability persists across multiple browser versions and security contexts, affecting both regular Firefox releases and extended support releases, indicating a systemic issue in the cookie parsing implementation that spans across different product lines.
Mitigation strategies for this vulnerability require immediate attention from system administrators and security teams responsible for browser deployment and user protection. The primary recommendation involves upgrading affected browser versions to the patched releases, specifically Firefox 141 and Thunderbird 141, along with their respective ESR versions. Organizations should implement comprehensive browser update policies to ensure all users operate on secure versions that address this cookie parsing vulnerability. Additionally, security teams should conduct thorough audits of existing cookie management practices and consider implementing additional monitoring for anomalous cookie behavior. The vulnerability aligns with CWE-1287, which addresses improper handling of cookie data, and relates to ATT&CK technique T1531 for credential access through cookie manipulation. Network security controls should be enhanced to detect and prevent the deployment of nameless cookies with equals signs in web applications, while application developers should validate cookie inputs more rigorously to prevent exploitation of this parsing inconsistency. System administrators should also consider implementing browser security policies that restrict cookie handling behavior and monitor for potential cookie shadowing events that could indicate exploitation attempts.