# CVE-2026-40016: Denial of service in OX Dovecot Pro

> Attackers can bypass Sieve CPU time limits via malicious scripts, degrading server performance and causing denial of service.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **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:** 12 May 2026
- **Updated:** 12 May 2026
- **Also known as:** ALPINE-CVE-2026-40016, AZL-86805, DEBIAN-CVE-2026-40016, GHSA-m97m-74mq-mqc6, SUSE-SU-2026:4271-1, UBUNTU-CVE-2026-40016

## What is CVE-2026-40016?

CVE-2026-40016 is a medium-severity denial of service vulnerability in Dovecot Dovecot, published on 12 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or alternatively prevent direct access to Sieve scripts via ManageSieve or local access. No publicly available exploits are known.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-40016?

It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `dovecot22` | SUSE:Linux Enterprise Server LTSS Extended Security 12 SP5 | All versions | 2.2.31-19.43.1 |

Products: Dovecot Dovecot, Open-Xchange Dovecot.

## How do I fix CVE-2026-40016?

Upgrade to a fixed version.

## Is CVE-2026-40016 being exploited?

There is no known exploitation of CVE-2026-40016 in the wild and no public exploit code.

## Other vulnerabilities in Dovecot Dovecot

- [CVE-2026-24031](https://insights.sbomify.com/CVE-2026-24031/): Auth bypass in OX Dovecot Pro (high 7.7)
- [CVE-2025-59032](https://insights.sbomify.com/CVE-2025-59032/): Denial of service in OX Dovecot Pro (high 7.5)
- [CVE-2026-27858](https://insights.sbomify.com/CVE-2026-27858/): Denial of service in OX Dovecot Pro (high 7.5)
- [CVE-2021-29157](https://insights.sbomify.com/CVE-2021-29157/): Path traversal in n/a (high 7.5)
- [CVE-2020-10957](https://insights.sbomify.com/CVE-2020-10957/): Null dereference in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40016 and fix it if it is affected.

What it is: CVE-2026-40016 is a medium-severity denial of service vulnerability in Dovecot Dovecot, published on 12 May 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-2026-40016 in the wild and no public exploit code.

Affected product: Dovecot Dovecot. 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-2026-40016/ (Markdown: https://insights.sbomify.com/CVE-2026-40016/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40016
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40016
- OSV: https://osv.dev/vulnerability/CVE-2026-40016

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40016/
Summaries are generated and may contain mistakes; the official description above is the record.