CVE-2026-102631 authd: Account takeover via username fallback in identity matching after IdP email reassignment
Attackers can hijack accounts and access sensitive files when identity providers reassign emails due to flawed username fallback logic in authd.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-102631?
CVE-2026-102631 is a medium-severity authentication bypass vulnerability in Canonical authd, published on 15 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In authd before 0.7.1, the user identity matching in UpdateUser (internal/users/manager.go) resolves an incoming login by the broker-scoped provider ID, but falls back to matching the username when the provider ID does not belong to any known user, and does not reject a conflicting non-empty provider ID. If an identity provider reassigns an email address, which authd uses as the username, to a new account, the new account inherits the previous user's local UID and home directory on its next login. This allows the new user to access and modify files belonging to the previous user, including credentials such as SSH keys and cloud API tokens, and silently rebinds the local account record to the new identity. As a mitigation, administrators should lock or delete the previous user's local authd account when the corresponding IdP account is removed.
Weakness: CWE-287
Which versions are affected by CVE-2026-102631?
How do I fix CVE-2026-102631?
Upgrade to a fixed version.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-102631 being exploited?
There is no known exploitation of CVE-2026-102631 in the wild and no public exploit code.
Sources
Also known as GHSA-92hm-xx6p-hch9, UBUNTU-CVE-2026-102631, USN-8957-1.