CVE-2024-1555 in Firefox
Summary
by MITRE • 02/20/2024
When opening a website using the `firefox://` protocol handler, SameSite cookies were not properly respected. This vulnerability affects Firefox < 123.
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Analysis
by VulDB Data Team • 04/19/2025
This vulnerability represents a critical breakdown in Firefox's cookie security mechanisms that occurred through improper handling of SameSite cookie attributes when processing firefox protocol handlers. The flaw specifically manifested when users navigated to websites using the firefox protocol scheme, which is commonly employed for deep linking into Firefox's internal components and web interfaces. The vulnerability allowed attackers to potentially bypass SameSite protections that are designed to prevent cross-site request forgery attacks by ensuring cookies are only sent with requests originating from the same site. This issue affected all Firefox versions prior to 123, creating a window of exposure where user sessions could be compromised through malicious web interactions.
The technical root cause stems from Firefox's protocol handler implementation not properly enforcing SameSite cookie policies during the processing of firefox:// URLs. When a browser encounters a firefox protocol link, it typically routes the request through internal Firefox components rather than standard HTTP processing pipelines. This special handling path bypassed the normal SameSite validation logic that would normally prevent cookies from being included in requests that cross site boundaries. The vulnerability essentially created an exception in Firefox's security model where cookies that should have been restricted based on SameSite policies were being sent regardless of the originating site context, effectively weakening the browser's protection against CSRF attacks.
The operational impact of this vulnerability extends beyond simple session hijacking to potentially enable more sophisticated attacks leveraging the bypassed security controls. An attacker could craft malicious websites that, when opened through firefox:// protocol handlers, could harvest sensitive cookies from authenticated sessions without proper SameSite protections. This weakness particularly affected scenarios where users might click on links within Firefox's own interface or when Firefox was used as a component in larger applications. The vulnerability was especially concerning because it operated at the browser protocol handler level, making it difficult to detect through standard network monitoring or web application firewalls that typically focus on HTTP traffic rather than protocol-specific interactions.
Organizations and users should immediately upgrade to Firefox version 123 or later to remediate this vulnerability, as the patch addresses the core issue in how Firefox processes protocol handlers and ensures that SameSite cookie policies are consistently enforced regardless of the navigation method used. Security teams should also implement monitoring for unusual firefox:// protocol usage patterns and consider configuring browser security policies that limit the exposure of sensitive cookies in contexts where protocol handlers might be invoked. The vulnerability aligns with CWE-346, which covers "Origin Validation Error", and maps to ATT&CK technique T1059.007 for the use of protocol handlers in malicious contexts. Additional mitigations include implementing Content Security Policy headers that restrict the use of protocol handlers and ensuring that sensitive applications do not rely solely on SameSite cookies for protection, as this vulnerability demonstrates that protocol-specific bypasses can undermine even well-designed cookie security mechanisms.