Authentication bypass by capture-replay in Open-Xchange GmbH OX Dovecot Pro
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- Required
- Attack complexity
- High
- Impact type
- Security bypass
- Confidentiality · integrity · availability
- High · High · None
- Fix status
- Deferred Red Hat: fix deferred
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat. Impact type from CWE-294.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Open-Xchange GmbH | OX Dovecot Pro | up to 2.3.0 | — | No fix listed | CNA |
- OX Dovecot Pro VendorOpen-Xchange GmbH Affected up to 2.3.0 Fixed in — No fix listed CNA
CPE configurations NVD · 2
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:dovecot:dovecot:*:*:*:*:*:*:*:* | before 2.4.3 | Vulnerable | The Dovecot Project |
| cpe:2.3:a:open-xchange:dovecot:*:*:*:*:pro:*:*:* | up to 2.3.0 | Vulnerable | Open-Xchange GmbH |
- cpe:2.3:a:dovecot:dovecot:*:*:*:*:*:*:*:* Versions before 2.4.3 Vulnerable ·The Dovecot Project
- cpe:2.3:a:open-xchange:dovecot:*:*:*:*:pro:*:*:* Versions up to 2.3.0 Vulnerable ·Open-Xchange GmbH
Remediation
No fixed version listed by the sources yet.
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 7 | Affected | No fix yet: Fix deferred |
Not affected: 3 products
- Red Hat Enterprise Linux 10
- Red Hat Enterprise Linux 8
- Red Hat Enterprise Linux 9
Timeline
- 2026-10-02 Threatist record created from CVE-2026-27855
- 2026-10-03 Alias added: GHSA-7923-h3mf-4442
References
More Open-Xchange GmbH Dovecot vulnerabilities
- TI-2026-22201 When safe filter is used with variable expansion, all following pipelines on the same… CVSS 3.1CRITICAL 9.1
- TI-2026-22208 Uncontrolled resource consumption in Open-Xchange GmbH OX Dovecot Pro CVSS 3.1HIGH 7.5
- TI-2025-36674 Improper input validation in Open-Xchange GmbH OX Dovecot Pro CVSS 3.1HIGH 7.5
- TI-2025-36670 Improper input validation in Open-Xchange GmbH OX Dovecot Pro CVSS 3.1HIGH 7.5
- TI-2026-19360 SQL injection in Open-Xchange GmbH OX Dovecot Pro CVSS 3.1HIGH 8.2
- TI-2026-22206 Improper authentication in Open-Xchange GmbH OX Dovecot Pro CVSS 3.1HIGH 7.4
Sources
- CVE-2026-27855 · CVE Program
- CVE-2026-27855 · NVD
- FIRST EPSS
- GHSA-7923-h3mf-4442 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-27855 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences