MediumFix available
dovecot — security advisory
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.
- Products
- dovecot
- Affected versions
- 1:2.3.19.1+dfsg1-2.1, 1:2.3.19.1+dfsg1-2.1+deb12u1, 1:2.4.1+dfsg1-6, 1:2.4.1+dfsg1-6+deb13u1, 1:2.4.1+dfsg1-6+deb13u2, 1:2.4.1+dfsg1-6+deb13u3, 1:2.4.1+dfsg1-7, 1:2.4.1+dfsg1-8, 1:2.4.1+dfsg1-9, 1:2.4.2+dfsg1-1, 1:2.4.2+dfsg1-2, 1:2.4.2+dfsg1-3, 1:2.4.2+dfsg1-4
- Fixed versions
- 1:2.3.19.1+dfsg1-2.1+deb12u2, 1:2.4.1+dfsg1-6+deb13u4, 1:2.4.3+dfsg1-1
- CVEs
- CVE-2026-27855
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 1 Nov 2026, 17:46 UTC · Revision 2
Source evidence
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.
osv:DEBIAN-CVE-2026-27855
dovecot
Fixed versions: 1:2.3.19.1+dfsg1-2.1+deb12u2
dovecot
Fixed versions: 1:2.4.1+dfsg1-6+deb13u4
dovecot
Fixed versions: 1:2.4.3+dfsg1-1
Complete source record
{
"id": "f206599488dc0e582e44f47b3e1b14f5bacf867e1763379d77b9724cc608273b",
"url": "https://osv.dev/vulnerability/DEBIAN-CVE-2026-27855",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "DEBIAN-CVE-2026-27855",
"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.",
"evidence": "osv:DEBIAN-CVE-2026-27855",
"products": [
{
"name": {
"value": "dovecot",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "1:2.3.19.1+dfsg1-2.1+deb12u2",
"evidence": "/affected/0/ranges"
}
],
"affected_versions": [
{
"value": "1:2.3.19.1+dfsg1-2.1",
"evidence": "/affected/0/versions"
},
{
"value": "1:2.3.19.1+dfsg1-2.1+deb12u1",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "dovecot",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "1:2.4.1+dfsg1-6+deb13u4",
"evidence": "/affected/1/ranges"
}
],
"affected_versions": [
{
"value": "1:2.4.1+dfsg1-6",
"evidence": "/affected/1/versions"
},
{
"value": "1:2.4.1+dfsg1-6+deb13u1",
"evidence": "/affected/1/versions"
},
{
"value": "1:2.4.1+dfsg1-6+deb13u2",
"evidence": "/affected/1/versions"
},
{
"value": "1:2.4.1+dfsg1-6+deb13u3",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
"value": "dovecot",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "1:2.4.3+dfsg1-1",
"evidence": "/affected/2/ranges"
}
],
"affected_versions": [
{
"value": "1:2.4.1+dfsg1-6",
"evidence": "/affected/2/versions"
},
{
"value": "1:2.4.1+dfsg1-7",
"evidence": "/affected/2/versions"
},
{
"value": "1:2.4.1+dfsg1-8",
"evidence": "/affected/2/versions"
},
{
"value": "1:2.4.1+dfsg1-9",
"evidence": "/affected/2/versions"
},
{
"value": "1:2.4.2+dfsg1-1",
"evidence": "/affected/2/versions"
},
{
"value": "1:2.4.2+dfsg1-2",
"evidence": "/affected/2/versions"
},
{
"value": "1:2.4.2+dfsg1-3",
"evidence": "/affected/2/versions"
},
{
"value": "1:2.4.2+dfsg1-4",
"evidence": "/affected/2/versions"
}
]
}
],
"severity": "medium",
"structured": {
"id": "DEBIAN-CVE-2026-27855",
"aliases": [
"DEBIAN-CVE-2026-27855"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "1:2.3.19.1+dfsg1-2.1+deb12u2"
}
]
}
],
"package": {
"name": "dovecot",
"purl": "pkg:deb/debian/dovecot?arch=source&distro=bookworm",
"ecosystem": "Debian:12"
},
"versions": [
"1:2.3.19.1+dfsg1-2.1",
"1:2.3.19.1+dfsg1-2.1+deb12u1"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-27855.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "1:2.4.1+dfsg1-6+deb13u4"
}
]
}
],
"package": {
"name": "dovecot",
"purl": "pkg:deb/debian/dovecot?arch=source&distro=trixie",
"ecosystem": "Debian:13"
},
"versions": [
"1:2.4.1+dfsg1-6",
"1:2.4.1+dfsg1-6+deb13u1",
"1:2.4.1+dfsg1-6+deb13u2",
"1:2.4.1+dfsg1-6+deb13u3"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-27855.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "1:2.4.3+dfsg1-1"
}
]
}
],
"package": {
"name": "dovecot",
"purl": "pkg:deb/debian/dovecot?arch=source&distro=forky",
"ecosystem": "Debian:14"
},
"versions": [
"1:2.4.1+dfsg1-6",
"1:2.4.1+dfsg1-7",
"1:2.4.1+dfsg1-8",
"1:2.4.1+dfsg1-9",
"1:2.4.2+dfsg1-1",
"1:2.4.2+dfsg1-2",
"1:2.4.2+dfsg1-3",
"1:2.4.2+dfsg1-4"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-27855.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
}
],
"modified": "2026-10-27T09:47:37.222832985Z",
"provider": "osv",
"upstream": [
"CVE-2026-27855"
],
"references": [
"https://security-tracker.debian.org/tracker/CVE-2026-27855"
]
},
"related_cves": [
{
"value": "CVE-2026-27855",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 461161,
"published_at": "2026-03-27T09:16:19.61+00:00"
}