# CVE-2026-27855: Auth bypass in OX Dovecot Pro

> Attackers can replay OTP credentials to log in as users if auth cache is enabled and usernames are altered, requiring secure connections or protocol changes.

- **Severity:** Medium 6.8 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 27 Mar 2026
- **Updated:** 27 Mar 2026
- **Also known as:** ALPINE-CVE-2026-27855, AZL-81701, DEBIAN-CVE-2026-27855, GHSA-7923-h3mf-4442, UBUNTU-CVE-2026-27855

## What is CVE-2026-27855?

CVE-2026-27855 is a medium-severity authentication bypass vulnerability in Dovecot Dovecot, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Dovecot OTP authentication is vulnerable to replay attack under specific conditions. If auth cache is enabled, and username is altered in passdb, then OTP credentials can be cached so that same OTP reply is valid. An attacker able to observe an OTP exchange is able to log in as the user. If authentication happens over unsecure connection, switch to SCRAM protocol. Alternatively ensure the communcations are secured, and if possible switch to OAUTH2 or SCRAM. No publicly available exploits are known.

Weakness: CWE-294 (Authentication Bypass by Capture-replay)

## Which versions are affected by CVE-2026-27855?

It affects 2 products.


Products: Dovecot Dovecot, Open-Xchange Dovecot.

## How do I fix CVE-2026-27855?

Change a configuration setting.

## Is CVE-2026-27855 being exploited?

There is no known exploitation of CVE-2026-27855 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-2026-27855 and fix it if it is affected.

What it is: CVE-2026-27855 is a medium-severity authentication bypass vulnerability in Dovecot Dovecot, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-27855 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-2026-27855/ (Markdown: https://insights.sbomify.com/CVE-2026-27855/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27855
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27855
- OSV: https://osv.dev/vulnerability/CVE-2026-27855

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27855/
Summaries are generated and may contain mistakes; the official description above is the record.