# CVE-2026-27858: Denial of service in OX Dovecot Pro

> An unauthenticated attacker can crash the managesieve service or exhaust memory via crafted messages, causing denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/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:** 27 Mar 2026
- **Updated:** 15 Jul 2026
- **Also known as:** AZL-81710, CLSA-2026-1778172123, CLSA-2026-1778173027, CLSA-2026-1785836865, CLSA-2026-1786619512, CLSA-2026-1786675596, CLSA-2026-1787231577, CLSA-2026-1787232011, DEBIAN-CVE-2026-27858, GHSA-xr7v-hj32-mr4r, UBUNTU-CVE-2026-27858

## What is CVE-2026-27858?

CVE-2026-27858 is a high-severity denial of service vulnerability in Dovecot Dovecot, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Attacker can send a specifically crafted message before authentication that causes managesieve to allocate large amount of memory.
 Attacker can force managesieve-login to be unavailable by repeatedly crashing the process. Protect access to managesieve protocol, or install fixed version. No publicly available exploits are known.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-27858?

It affects 2 products.


Products: Dovecot Dovecot, Open-Xchange Dovecot.

## How do I fix CVE-2026-27858?

Upgrade to a fixed version.

## Is CVE-2026-27858 being exploited?

There is no known exploitation of CVE-2026-27858 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-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)
- [CVE-2020-7046](https://insights.sbomify.com/CVE-2020-7046/): Denial of service in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-27858 and fix it if it is affected.

What it is: CVE-2026-27858 is a high-severity denial of service vulnerability in Dovecot Dovecot, published on 27 Mar 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-2026-27858 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-2026-27858/ (Markdown: https://insights.sbomify.com/CVE-2026-27858/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27858
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27858
- OSV: https://osv.dev/vulnerability/CVE-2026-27858

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27858/
Summaries are generated and may contain mistakes; the official description above is the record.