# CVE-2026-33263: Denial of service in OX Dovecot CE

> Attackers can crash the submission-login process by exhausting file descriptors, causing service disruption or duplicate message deliveries in specific configurations.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L`)
- **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-2026-33263, AZL-98313, DEBIAN-CVE-2026-33263, GHSA-9rqj-cvwq-v6qh, UBUNTU-CVE-2026-33263

## What is CVE-2026-33263?

CVE-2026-33263 is a medium-severity denial of service 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

When mail_max_userip_connections is set (default 10) and reached, submission-login can crash with epoll() panic caused by file descriptor handling issues. If running in high-security mode (default for community releases), only the new submission connection gets terminated. If running in high-performance mode (default for Pro releases), all connections handled by the submission-login process will be terminated. The crashes can cause failure for user to send a message, or it can cause duplicate messages to be sent. If TLS is not used (in the backend server processing the submission), duplicate deliveries cannot happen, because the crash can only happen at AUTH stage. Limit the number of connections handled by single submission-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.

Weakness: CWE-403 (Exposure of File Descriptor to Unintended Control Sphere)

## Which versions are affected by CVE-2026-33263?


## How do I fix CVE-2026-33263?

Upgrade to a fixed version.

## Is CVE-2026-33263 being exploited?

There is no known exploitation of CVE-2026-33263 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33263 and fix it if it is affected.

What it is: CVE-2026-33263 is a medium-severity denial of service 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-2026-33263 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-2026-33263/ (Markdown: https://insights.sbomify.com/CVE-2026-33263/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33263
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33263
- OSV: https://osv.dev/vulnerability/CVE-2026-33263

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33263/
Summaries are generated and may contain mistakes; the official description above is the record.