Vulnerability · Published Oct 15, 2026 · Assigned by canonical
CVE-2026-102631authd: Account takeover via username fallback in identity matching after IdP email reassignment
Medium 5.9
In plain English
A medium-severity improper authentication in authd from Canonical. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 1% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu:26.04:LTS | authd | no fix listed | UBUNTU-CVE-2026-102631 |
| Ubuntu:26.10 | authd | 0.7.1 | USN-8957-1 |
| Ubuntu:26.10 | authd | 0.7.1 | UBUNTU-CVE-2026-102631 |
Affected products (as reported)
Weakness: CWE-287 · Vector: CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
References
- https://github.com/canonical/authd/pull/2067 patch
- https://bugs.launchpad.net/ubuntu/+source/authd/+bug/2168531 issue-tracking
- https://ubuntu.com/security/CVE-2026-102631 vendor-advisory