# CVE-2026-40019: Denial of service in OX Dovecot CE

> An unauthenticated attacker can cause a denial of service by sending a truncated quoted argument to the ManageSieve login process, leading to infinite CPU consumption.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **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-2026-40019, DEBIAN-CVE-2026-40019, GHSA-c3mr-h4j4-h26r, UBUNTU-CVE-2026-40019

## What is CVE-2026-40019?

CVE-2026-40019 is a medium-severity denial of service vulnerability in Open-Xchange GmbH OX Dovecot CE, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An unauthenticated attacker can send a truncated quoted argument to the ManageSieve login process, which makes it spin in an infinite loop consuming CPU. This can cause degradation or denial of service for Sieve script management, and repeated connections can consume all available CPU on the server. Monitor system for abnormal CPU usage and kill the offending process. Restrict network access to the ManageSieve service to trusted clients. Update to non-vulnerable version. No publicly available exploits are known.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-40019?


## How do I fix CVE-2026-40019?

Upgrade to a fixed version.

## Is CVE-2026-40019 being exploited?

There is no known exploitation of CVE-2026-40019 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40019 and fix it if it is affected.

What it is: CVE-2026-40019 is a medium-severity denial of service vulnerability in Open-Xchange GmbH OX Dovecot CE, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-40019 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-2026-40019/ (Markdown: https://insights.sbomify.com/CVE-2026-40019/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40019
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40019
- OSV: https://osv.dev/vulnerability/CVE-2026-40019

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40019/
Summaries are generated and may contain mistakes; the official description above is the record.