CVE-2026-56750: Gitea Remember-Me Token Theft Not Invalidating Attacker Session

The vulnerability is in the Remember-Me (gitea_incredible) token validation logic, specifically when handling a compromised token (hash mismatch).

The vulnerable function is this one:

https://github.com/go-gitea/gitea/blob/689ace1ce28fd74244b8aa335d9928cdbf6b22f9/services/auth/auth_token.go#L33-L64

Affected Endpoint

POST /user/login (and any endpoint triggering autoSignIn via the Remember-Me cookie).

Description

Gitea implements Remember-Me cookies using a split token design (ID:Hash), citing the Paragonie secure remember-me guide. When a token is used, its Hash is rotated, but the ID remains the same.

If an attacker steals a user's Remember-Me token and uses it to authenticate, the attacker is issued a new rotated token (same ID, new Hash). When the legitimate user later attempts to use their original token, Gitea correctly detects a hash mismatch for the given ID.

According to the referenced Paragonie specification, this indicates a compromised token, and ALL active remember-me sessions for that user MUST be invalidated. However, Gitea's CheckAuthToken function simply returns ErrAuthTokenInvalidHash. The calling code (autoSignIn) catches this error and deletes the victim's local cookie via ctx.DeleteSiteCookie, but fails to delete the compromised token from the database.

As a result, the attacker's active session is never invalidated, and the attacker maintains persistent, indefinite access to the victim's account, entirely defeating the purpose of the split-token security design.