# CVE-2026-27857: Denial of service in OX Dovecot Pro

> An attacker can cause a denial of service by sending crafted NOOP commands that exhaust server memory, requiring an upgrade to the fixed version.

- **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:** 27 Mar 2026
- **Updated:** 15 Jul 2026
- **Also known as:** ALPINE-CVE-2026-27857, AZL-81707, CLSA-2026-1777976700, CLSA-2026-1777977059, CLSA-2026-1777978787, CLSA-2026-1778022490, CLSA-2026-1778238067, CLSA-2026-1778250399, CLSA-2026-1778250885, CLSA-2026-1778750122, CLSA-2026-1778882329, DEBIAN-CVE-2026-27857, GHSA-j26c-8p6m-gpfj, UBUNTU-CVE-2026-27857

## What is CVE-2026-27857?

CVE-2026-27857 is a medium-severity denial of service vulnerability in Dovecot Dovecot, published on 27 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Sending "NOOP (((...)))" command with 4000 parenthesis open+close results in ~1MB extra memory usage. Longer commands will result in client disconnection. This 1 MB can be left allocated for longer time periods by not sending the command ending LF. So attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Install fixed version, there is no other remediation. 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-2026-27857?

It affects 2 products.


Products: Dovecot Dovecot, Open-Xchange Dovecot.

## How do I fix CVE-2026-27857?

Upgrade to a fixed version.

## Is CVE-2026-27857 being exploited?

There is no known exploitation of CVE-2026-27857 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-2026-27857 and fix it if it is affected.

What it is: CVE-2026-27857 is a medium-severity denial of service vulnerability in Dovecot Dovecot, published on 27 Mar 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-2026-27857 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-2026-27857/ (Markdown: https://insights.sbomify.com/CVE-2026-27857/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27857
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27857
- OSV: https://osv.dev/vulnerability/CVE-2026-27857

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27857/
Summaries are generated and may contain mistakes; the official description above is the record.