CVE-2026-102631

authd: Account takeover via username fallback in identity matching after IdP email reassignment

Published Oct 15, 2026 CVSS 4.0 · 5.9 Medium EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Ubuntu USN Ubuntu USN USN-8957-1 authd vulnerability
History
Type Values Removed Values Added
First Time appeared Canonical
Canonical authd
Vendors & Products Canonical
Canonical authd
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Title authd: Account takeover via username fallback in identity matching after IdP email reassignment
Weaknesses CWE-287
References
Metrics cvssV4_0

{'score': 5.9, '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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
canonical
Published
Updated
Oct 16, 2026, 8:16 PM
Reserved
Sep 29, 2026, 3:27 PM
Status
Deferred
Published
Oct 15, 2026, 5:17 PM
Modified
Oct 16, 2026, 9:17 PM