CVE-2025-55031 in Firefox
Summary
by MITRE • 08/20/2025
Malicious pages could use Firefox for iOS to pass FIDO: links to the OS and trigger the hybrid passkey transport. An attacker within Bluetooth range could have used this to trick the user into using their passkey to log the attacker's computer into the target account. This vulnerability affects Firefox for iOS < 142 and Focus for iOS < 142.
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Analysis
by VulDB Data Team • 10/12/2025
This vulnerability represents a critical security flaw in Firefox for iOS and Focus for iOS applications that could enable unauthorized account access through manipulation of the FIDO2 passkey authentication system. The issue stems from improper handling of FIDO: protocol links within the mobile browser environment, creating an attack vector where malicious web pages could exploit the hybrid passkey transport mechanism to deceive users into authenticating with attacker-controlled systems. The vulnerability specifically affects versions prior to 142, indicating a regression or oversight in the implementation of secure communication protocols between the browser and operating system's passkey infrastructure.
The technical flaw exploits the trust relationship between the iOS browser and the operating system's FIDO2 implementation by leveraging the hybrid passkey transport mechanism. When a user encounters a malicious page, the page can programmatically initiate FIDO: links that bypass normal browser security boundaries and directly communicate with the iOS system's authentication services. This creates an unintended pathway where the passkey authentication process can be manipulated to authenticate with arbitrary systems rather than the intended service provider. The vulnerability essentially allows attackers to intercept and redirect passkey authentication flows through the iOS Bluetooth interface, which is designed for legitimate device pairing but becomes exploitable when combined with the browser's insufficient validation of FIDO: link origins.
The operational impact of this vulnerability is severe as it enables credential theft and unauthorized account access through a sophisticated social engineering attack vector. An attacker within Bluetooth range could potentially intercept passkey authentication requests and redirect them to their own system, effectively allowing them to authenticate as the user on target accounts. This represents a significant compromise of the authentication security model, as passkeys are designed to be secure, phishing-resistant credentials that should only authenticate to the legitimate service provider. The attack requires only proximity to the victim's device and access to a malicious webpage, making it particularly dangerous in public environments or when users are browsing untrusted websites. The vulnerability undermines the fundamental security guarantees that passkey authentication provides, potentially allowing attackers to access sensitive accounts, personal data, and enterprise systems that rely on this authentication method.
This vulnerability aligns with CWE-352, which addresses Cross-Site Request Forgery, and represents a specific instance of improper input validation in the context of FIDO2 protocol handling. The attack pattern follows techniques described in the ATT&CK framework under T1566 for phishing and T1071 for application layer protocols, specifically targeting the authentication and credential access phases of an attack chain. The hybrid passkey transport mechanism that enables this vulnerability is designed to facilitate seamless authentication between devices but becomes a security risk when the browser fails to properly validate the authenticity and intended recipient of FIDO: protocol requests. Organizations should ensure immediate deployment of patched versions to prevent exploitation, while users should be educated about the risks of visiting untrusted websites and the importance of keeping their browser software up to date.
Mitigation strategies should focus on immediate software updates to versions 142 or later where the vulnerability has been addressed through proper validation of FIDO: link origins and enhanced isolation of passkey authentication flows. Security teams should implement monitoring for suspicious FIDO2 protocol usage patterns and consider temporary restrictions on passkey usage in high-risk environments. The fix likely involves strengthening the browser's protocol handling to ensure that FIDO: links can only be processed by legitimate service providers and cannot be redirected to arbitrary systems. Additionally, users should be advised to avoid browsing untrusted websites when passkey authentication is active and to regularly update their mobile browser applications to maintain security against such sophisticated attack vectors that exploit the intersection of web browser security and operating system authentication mechanisms.