# CVE-2026-40205: Auth bypass in OX Dovecot CE

> Attackers with partial OAuth2 scopes can bypass authorization checks in remote token validation, gaining unauthorized access to Dovecot services.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Aug 2026
- **Updated:** 28 Aug 2026
- **Also known as:** ALPINE-CVE-2026-40205, AZL-98307, DEBIAN-CVE-2026-40205, GHSA-8rjh-g9p7-rx87, UBUNTU-CVE-2026-40205

## What is CVE-2026-40205?

CVE-2026-40205 is a medium-severity authentication bypass vulnerability in Open-Xchange GmbH OX Dovecot CE, published on 28 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

An attacker that holds an OAuth2 token granting only part of the required scopes can authenticate, because when more than one scope is required in the configuration, the remote token validation paths accept a token that carries only one of them, while the local token validation path correctly requires all of them. The configured authorization policy is not enforced, so a token that was granted only part of the required permissions is accepted where it should have been rejected. Use local token validation where tokens can be validated locally. Update to non-vulnerable version. No publicly available exploits are known.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2026-40205?


## How do I fix CVE-2026-40205?

Upgrade to a fixed version.

## Is CVE-2026-40205 being exploited?

There is no known exploitation of CVE-2026-40205 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40205 and fix it if it is affected.

What it is: CVE-2026-40205 is a medium-severity authentication bypass vulnerability in Open-Xchange GmbH OX Dovecot CE, published on 28 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-40205 in the wild and no public exploit code.

Affected product: Open-Xchange GmbH OX Dovecot CE. 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-2026-40205/ (Markdown: https://insights.sbomify.com/CVE-2026-40205/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40205
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40205
- OSV: https://osv.dev/vulnerability/CVE-2026-40205

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40205/
Summaries are generated and may contain mistakes; the official description above is the record.