EUVD-2026-27424Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
4DescriptionGitHub Advisory
Vaultwarden is a Bitwarden-compatible server written in Rust. In versions 1.35.4 and earlier, the WebAuthn authentication flow in validate_webauthn_login() updates persistent credential metadata (1backup_eligible1 and 1backup_state flags1) based on unverified authenticatorData before signature validation is performed. An attacker who knows a user's password but cannot produce a valid WebAuthn signature can permanently modify the stored backup flags for that user's credential. If signature verification fails, the database update is not rolled back. This can result in a persistent denial of service of WebAuthn two-factor authentication for affected credentials. This issue has been fixed in version 1.35.5.
AnalysisAI
Vaultwarden versions 1.35.4 and earlier allow authenticated attackers to permanently disable WebAuthn two-factor authentication for user credentials by exploiting a logic flaw in the validate_webauthn_login() function that updates backup eligibility flags before validating the WebAuthn signature. An attacker with knowledge of a user's password can modify these persistent flags even when providing an invalid WebAuthn signature, causing signature verification to fail without rolling back the database changes, resulting in denial of service of the 2FA mechanism for affected credentials. The vulnerability has been patched in version 1.35.5.
Technical ContextAI
Vaultwarden is a self-hosted Bitwarden-compatible password manager server written in Rust. The vulnerability exists in the WebAuthn authentication flow, specifically in the validate_webauthn_login() function which handles FIDO2/WebAuthn credential verification. The root cause (CWE-345: Insufficient Verification of Data Authenticity) is a transaction ordering flaw where the application updates backup-related credential metadata (backup_eligible and backup_state flags) in the database before cryptographically validating the WebAuthn signature. This violates secure coding principles for authentication systems where all validation must complete successfully before persisting state changes. The WebAuthn standard (CTAP2/FIDO2) requires signature verification as a fundamental security control; premature database updates expose this critical control to bypass.
RemediationAI
Upgrade to Vaultwarden version 1.35.5 or later immediately. The patch moves the backup flag updates to occur only after successful WebAuthn signature verification, ensuring database state remains consistent with authentication success or failure. For environments unable to upgrade immediately, disable WebAuthn authentication as a temporary compensating control, though this reduces the security posture for all users relying on FIDO2 2FA. Monitor authentication logs for failed WebAuthn attempts combined with database modifications to detect potential exploitation attempts. Two-factor remember tokens are now limited to a maximum of 30 days validity after upgrade, and old tokens are immediately invalidated; users will need to re-authenticate on previously remembered devices. If you override admin templates, review and update them post-upgrade due to admin template changes in 1.35.5. See GitHub Security Advisory GHSA-x7g7-cgx5-jhx2 and release notes at https://github.com/dani-garcia/vaultwarden/releases/tag/1.35.5 for complete details.
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External POC / Exploit Code
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