# CVE-2026-42395: Open-Xchange Dovecot denial of service via NUL byte in trusted proxy forwarding

Source: https://junglewise.ai/threats/cve-2026-42395-open-xchange-dovecot-denial-of-service-via-nul-byte-in-trusted  
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-2026-42395 · Severity: medium · CVSS 4.3 · Published 2026-08-28

OX Dovecot Pro is an email server that handles user authentication and mail operations. A trusted proxy host can send specially crafted forwarding information containing a NUL byte, which crashes the login process and prevents users from authenticating. This causes service unavailability for affected users. Only deployments that explicitly configure trusted proxy networks are vulnerable.

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-2026-42395 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42395 being exploited in the wild.

**How severe is CVE-2026-42395?** Medium severity, with a CVSS score of 4.3, 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-2026-42395?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-42395 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-42395?** 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

The vulnerability is a denial-of-service condition in OX Dovecot Pro's login process triggered by malformed forwarding headers from a host configured as a trusted proxy. When a trusted proxy sends forwarding information containing a NUL byte, the login process crashes on the next authentication attempt, terminating the session. The attack vector is network-based and requires the attacker to control or compromise a host listed in the trusted proxy configuration. No publicly available exploits are known. Affected versions: 2.3.0–2.3.22.1, 3.0.0–3.0.6, and 3.1.0–3.1.5; patched versions are 2.3.22.2, 3.0.7, and 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: CVE-2026-42395 publicly disclosed

## 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 information disclosure in IMAP URLFETCH](https://junglewise.ai/threats/cve-2026-42392-open-xchange-dovecot-information-disclosure-in-imap-urlfetch)