{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-27855", "assignerOrgId": "8ce71d90-2354-404b-a86e-bec2cc4e6981", "state": "PUBLISHED", "assignerShortName": "OX", "dateReserved": "2026-02-24T08:46:09.373Z", "datePublished": "2026-03-27T08:10:18.821Z", "dateUpdated": "2026-03-27T08:10:18.821Z"}, "containers": {"cna": {"affected": [{"defaultStatus": "unaffected", "modules": ["core"], "product": "OX Dovecot Pro", "vendor": "Open-Xchange GmbH", "versions": [{"lessThanOrEqual": "2.3.0", "status": "affected", "version": "0", "versionType": "semver"}]}], "descriptions": [{"lang": "en", "value": "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."}], "metrics": [{"cvssV3_1": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 6.8, "baseSeverity": "MEDIUM", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "REQUIRED", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N", "version": "3.1"}, "format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "problemTypes": [{"descriptions": [{"cweId": "CWE-294", "description": "Authentication Bypass by Capture-replay", "lang": "en", "type": "cwe"}]}], "providerMetadata": {"orgId": "8ce71d90-2354-404b-a86e-bec2cc4e6981", "shortName": "OX", "dateUpdated": "2026-03-27T08:10:18.821Z"}, "references": [{"tags": ["vendor-advisory"], "url": "https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0001.json"}], "source": {"defect": "DOV-8859", "discovery": "EXTERNAL"}}}}

{}

{"cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "id": "CVE-2026-27855", "lastModified": "2026-03-27T09:16:19.610", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 6.8, "baseSeverity": "MEDIUM", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "REQUIRED", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N", "version": "3.1"}, "exploitabilityScore": 1.6, "impactScore": 5.2, "source": "security@open-xchange.com", "type": "Secondary"}]}, "published": "2026-03-27T09:16:19.610", "references": [{"source": "security@open-xchange.com", "url": "https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0001.json"}], "sourceIdentifier": "security@open-xchange.com", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-294"}], "source": "security@open-xchange.com", "type": "Secondary"}]}

{}

{"analysis": {"en": {"generated_at": "2026-03-27T09:37:05.082688+00:00", "value": {"mitigation_remediation": ["Disable OTP authentication or stop using caching for OTP.", "Enforce TLS for all authentication traffic to prevent interception.", "Configure Dovecot to use stronger authentication such as SCRAM or OAUTH2.", "Upgrade to the latest OX Dovecot Pro release that addresses the issue.", "Monitor authentication logs for unusual OTP usage patterns.", "Review passdb configuration to prevent unintended username alterations."], "summary": {"action": "Patch Now", "impact": "Unauthorized authentication via OTP replay"}, "threat_synthesis": {"affected_systems": "Affected systems are Open\u2011Xchange GmbH OX Dovecot Pro clients. No specific version range is listed; administrators should verify that their installation uses a version that supports OTP caching and passdb modifications. Any deployment employing OTP authentication with caching enabled is potentially impacted.", "description_and_impact": "An OTP authentication mechanism in OX Dovecot Pro allows replay attacks when authentication caching is enabled and the username is modified in the passdb. Cached OTP credentials can be reused, enabling an attacker who intercepts an OTP exchange to authenticate as the victim. The weakness permits unauthorized access to user accounts without knowing the password, effectively bypassing authentication mechanisms.", "risk_and_exploitability": "With a CVSS score of 6.8 the vulnerability is considered medium\u2011high severity. EPSS information is unavailable, and the issue is not in the KEV catalogue, but the required conditions are relatively specific. The likely attack vector involves an attacker observing an OTP challenge/response over an insecure connection, then replaying the response after the username has been altered in the back\u2011end. No exploits have been published yet; however, the logic of the replay attack makes it feasible for an adversary capable of collecting the OTP exchange to hijack a session."}}}}, "created": "2026-03-27T09:45:44.840515+00:00", "title": "Dovecot OTP Replay Allows Unauthorized Authentication", "updated": "2026-03-27T09:45:44.840537+00:00", "vendors": []}