# 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.

- **Severity:** Medium 5.9 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Oct 2026
- **Updated:** 16 Oct 2026
- **Also known as:** GHSA-92hm-xx6p-hch9, UBUNTU-CVE-2026-102631, USN-8957-1

## 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 (Improper Authentication)

## Which versions are affected by CVE-2026-102631?


## How do I fix CVE-2026-102631?

Upgrade to a fixed version.

## Is CVE-2026-102631 being exploited?

There is no known exploitation of CVE-2026-102631 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-102631 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-102631 in the wild and no public exploit code.

Affected product: Canonical authd. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-102631/ (Markdown: https://insights.sbomify.com/CVE-2026-102631/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-102631
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-102631
- OSV: https://osv.dev/vulnerability/CVE-2026-102631

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-102631/
Summaries are generated and may contain mistakes; the official description above is the record.