Vaultwarden, a Rust‑based Bitwarden‑compatible server, had a flaw in its SSO authorization flow before version 1.36.0. The OAuth state parameter handled by /connect/authorize was not tied to the initiating browser session, attacker‑controlled PKCE parameters were accepted, and SsoAuth records persisted after failed token exchanges. These oversights allow an unauthenticated attacker to trigger authentication with an external IdP, then redeem the resulting tokens to obtain a fully authenticated Vaultwarden session. The issue is fixed in 1.36.0. This vulnerability is a Cross‑Site Request Forgery (CWE‑352).

The issue affects all instances of the Vaultwarden server managed by dani‑garcia that are running a version before 1.36.0. Versions 1.36.0 and later contain the fix.

The CVSS base score of 8.3 indicates a high severity hit. The EPSS score, listed as < 1%, suggests that exploitation attempts are rare, and the vulnerability is not in the CISA KEV catalog. From the description, the attack appears to require only a remote HTTP request to the /connect/authorize endpoint, indicating a web‑based attack vector that does not need privileged local access. This inference is drawn from the fact that the flaw involves the OAuth state parameter being unbound to the session.