# CVE-2026-40018: Open-Xchange Dovecot authentication bypass

Source: https://junglewise.ai/threats/cve-2026-40018-open-xchange-dovecot-authentication-bypass  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-28. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-40018 · Severity: high · CVSS 7.4 · Published 2026-08-28

OX Dovecot is an email server component that handles mail access and authentication for enterprise messaging systems. A critical authentication vulnerability allows attackers to bypass login controls and gain unauthorized access to user mailboxes and email data without valid credentials.

Technologies: [Open-Xchange Dovecot Pro](https://junglewise.ai/threats/technologies/dovecot-pro). Vendors: [Open-Xchange](https://junglewise.ai/threats/vendors/open-xchange).

## Quick answers

**Is CVE-2026-40018 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-40018 being exploited in the wild.

**How severe is CVE-2026-40018?** High severity, with a CVSS score of 7.4, published 28 August 2026.

**Which products and versions are affected?** Open-Xchange Dovecot Pro 2.3.0 to 2.3.22.1, 3.0.0 to 3.0.6, 3.1.0 to 3.1.5.

**Is there a fix for CVE-2026-40018?** A patch was published on 2026-08-28: Updates available: 2.3.22.2, 3.0.7, 3.1.6 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-40018 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-40018?** Check whether you run Open-Xchange Dovecot Pro at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

This vulnerability is a critical authentication bypass in OX Dovecot Pro. The root cause and specific attack vector are not detailed in the available advisory excerpt, but the CVSS score of 7.4 and "critical" aggregate severity indicate a high-impact flaw affecting core authentication mechanisms. Affected versions include 2.3.0 through 2.3.22.1, 3.0.0 through 3.0.6, and 3.1.0 through 3.1.5. The flaw is network-accessible and requires no user interaction. Patches are available: upgrade to 2.3.22.2, 3.0.7, or 3.1.6.

## Affected products

- Open-Xchange Dovecot Pro 2.3.0 to 2.3.22.1, 3.0.0 to 3.0.6, 3.1.0 to 3.1.5

## Timeline

- 2026-08-28: disclosed
- 2026-08-28: patched: Updates available: 2.3.22.2, 3.0.7, 3.1.6

## References

- [https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0003.json](https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0003.json)

## Related threats

- [Open-Xchange Dovecot stack exhaustion denial of service](https://junglewise.ai/threats/cve-2026-73209-open-xchange-dovecot-stack-exhaustion-denial-of-service)
- [Open-Xchange Dovecot OAuth2 token scope validation bypass](https://junglewise.ai/threats/cve-2026-73208-open-xchange-dovecot-oauth2-token-scope-validation-bypass)
- [Open-Xchange Dovecot denial of service via IMAP compression](https://junglewise.ai/threats/cve-2026-52687-open-xchange-dovecot-denial-of-service-via-imap-compression)
- [Open-Xchange Dovecot Sieve CPU resource accounting bypass](https://junglewise.ai/threats/cve-2026-52681-open-xchange-dovecot-sieve-cpu-resource-accounting-bypass)
- [Open-Xchange Dovecot denial of service via NUL byte in trusted proxy forwarding](https://junglewise.ai/threats/cve-2026-42395-open-xchange-dovecot-denial-of-service-via-nul-byte-in-trusted)