# CVE-2026-73209: Open-Xchange Dovecot stack exhaustion denial of service

Source: https://junglewise.ai/threats/cve-2026-73209-open-xchange-dovecot-stack-exhaustion-denial-of-service  
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-2026-73209 · Severity: medium · CVSS 6.5 · Published 2026-08-28

OX Dovecot Pro is an IMAP email server used to handle incoming and outgoing mail for organizations. An authenticated attacker can send specially crafted compressed data that exhausts the server's stack memory, causing the IMAP process to crash and resulting in email service unavailability for affected users.

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-2026-73209 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-73209 being exploited in the wild.

**How severe is CVE-2026-73209?** Medium severity, with a CVSS score of 6.5, published 28 August 2026.

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

**Is there a fix for CVE-2026-73209?** 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-2026-73209 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-73209?** 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 stack exhaustion flaw triggered by malformed compressed data in the IMAP protocol. An attacker with valid IMAP credentials can exploit this by sending crafted compressed payloads that cause recursive or deep stack consumption, leading to a crash of the IMAP daemon process. The attack requires authentication, limiting exposure to users with valid accounts or to scenarios where credential compromise has occurred. The result is a denial of service: the IMAP service becomes unavailable until the process is manually or automatically restarted. Patches are available in OX Dovecot Pro versions 2.3.22.2, 3.0.7, and 3.1.6 or later.

## Affected products

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

## Timeline

- 2026-08-28: disclosed
- 2026-08-26: advisory: OXDC-ADV-2026-0003 initial release

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