CVE-2026-102631: authd: Account takeover via username fallback in identity matching after IdP email reassignment

Severity: medium (CVSS 5.9 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-15 · updated 2026-10-16
Weakness: CWE-287

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 products

Canonical authd: from 0.1 before 0.7.1; from 0.1 before 0.7.1~ubuntu24.04.1; from 0.1 before 0.7.1~ubuntu26.04 — fixed in 0.7.1, 0.7.1~ubuntu24.04.1, 0.7.1~ubuntu26.04

How to fix

Upgrade to a fixed version: Canonical authd 0.7.1, 0.7.1~ubuntu24.04.1, 0.7.1~ubuntu26.04. Check the vendor advisory for mitigations.

References

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