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Ox Dovecot Pro EUVDEUVD-2026-16565

| CVE-2026-27856 MEDIUM
Improper Authentication (CWE-287)
2026-03-27 OX
Oracle Authentication Bypass Ox Dovecot Pro
5.9
CVSS 3.1 · NVD
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Severity by source

NVD PRIMARY
5.9 MEDIUM
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Ubuntu
MEDIUM
qualitative
SUSE
7.4 HIGH
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Red Hat
7.4 HIGH
qualitative

Primary rating from NVD.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

Lifecycle Timeline

7
Severity Changed
Jun 30, 2026 - 03:24 NVD
HIGH MEDIUM
CVSS changed
Jun 30, 2026 - 03:24 NVD
7.4 (HIGH) 5.9 (MEDIUM)
Re-analysis Queued
Apr 29, 2026 - 19:37 vuln.today
cvss_changed
Patch released
Mar 31, 2026 - 13:49 nvd
Patch available
EUVD ID Assigned
Mar 27, 2026 - 08:30 euvd
EUVD-2026-16565
Analysis Generated
Mar 27, 2026 - 08:30 vuln.today
CVE Published
Mar 27, 2026 - 08:10 nvd
HIGH 7.4

DescriptionNVD

Doveadm credentials are verified using direct comparison which is susceptible to timing oracle attack. An attacker can use this to determine the configured credentials. Figuring out the credential will lead into full access to the affected component. Limit access to the doveadm http service port, install fixed version. No publicly available exploits are known.

AnalysisAI

OX Dovecot Pro's doveadm HTTP service is vulnerable to timing oracle attacks during credential verification, allowing remote unauthenticated attackers to enumerate valid credentials through timing analysis and gain full administrative access to the doveadm management interface. The vulnerability affects OX Dovecot Pro installations with exposed doveadm HTTP service ports, carries a CVSS score of 7.4, and has no public exploit identified at time of analysis.

Technical ContextAI

The vulnerability resides in the doveadm HTTP service authentication mechanism of OX Dovecot Pro (CPE cpe:2.3:a:open-xchange_gmbh:ox_dovecot_pro). The root cause is CWE-287 (Improper Authentication) stemming from direct string comparison during credential verification instead of constant-time comparison functions. In timing oracle attacks, attackers measure the time required to validate credentials; non-constant-time comparison operations terminate early when a character mismatch is found, creating measurable timing differences that reveal information about the correct credential string character-by-character. The doveadm service is Dovecot's administrative interface providing mailbox and user management capabilities, making credential compromise particularly severe.

RemediationAI

Install the fixed version as specified in the Open-Xchange security advisory at https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0001.json, which addresses the timing oracle vulnerability through constant-time credential comparison. As an immediate mitigation measure, restrict network access to the doveadm HTTP service port using firewall rules or network segmentation to limit exposure only to trusted administrative networks, preventing remote attackers from conducting timing oracle attacks. Organizations should review current doveadm service configurations to ensure the management interface is not exposed to untrusted networks and implement IP allowlisting for authorized administrative hosts.

More in Ox Dovecot Pro

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CVE-2026-27851 CRITICAL
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Authentication-layer injection in OX Dovecot Pro (versions up to and including 2.4.3 and 3.1.4) arises from a flaw in th
CVE-2026-24031 HIGH
8.2 Mar 27

Authentication bypass and user enumeration in OX Dovecot Pro (versions up to and including 3.1.0 and the 2.4.x line up t
CVE-2025-59032 HIGH
7.5 Mar 27

OX Dovecot Pro ManageSieve service crashes when processing AUTHENTICATE commands with SASL initial responses using liter
CVE-2026-27858 HIGH
7.5 Mar 27

OX Dovecot Pro managesieve-login process crashes repeatedly due to memory exhaustion triggered by unauthenticated attack
CVE-2026-27857 HIGH
7.5 Mar 27

Remote memory-exhaustion denial of service in OX Dovecot Pro (versions up to and including 2.3.0) lets an unauthenticate
CVE-2025-59028 MEDIUM
5.3 Mar 27

OX Dovecot Pro authentication server becomes disconnected when processing invalid base64 SASL data, causing all concurre
CVE-2026-0394 MEDIUM
5.3 Mar 27

Path traversal in OX Dovecot Pro allows unauthenticated remote attackers to read arbitrary files such as /etc/passwd whe
CVE-2026-27859 MEDIUM
5.3 Mar 27

OX Dovecot Pro mail delivery processes consume excessive CPU resources when processing mail messages containing abnormal
CVE-2025-59031 MEDIUM
4.3 Mar 27

Dovecot's text conversion script for OOXML attachments unsafely processes zip-style files, allowing authenticated attack
CVE-2026-42006 MEDIUM
4.3 May 12

OX Dovecot Pro allows authenticated attackers to cause uncontrolled memory consumption and denial of service via excessi
CVE-2026-40020 LOW
3.1 May 12

OX Dovecot Pro is vulnerable to IMAP SETACL command injection that allows authenticated users to bypass the imap_acl_all

Same weakness CWE-287 – Improper Authentication

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CVE-2020-0688 HIGH POC
8.8
CVE-2023-46805 HIGH POC
8.2
CVE-2015-1187 CRITICAL POC
9.8
CVE-2024-7593 CRITICAL POC
9.8
CVE-2017-7921 CRITICAL POC
9.8
CVE-2024-53704 CRITICAL POC
9.8
CVE-2015-7755 CRITICAL POC
9.8
CVE-2013-0625 CRITICAL POC
9.8

Same technique Authentication Bypass

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CVE-2023-22515 CRITICAL POC
9.8
CVE-2012-4681 CRITICAL POC
9.8
CVE-2013-2465 CRITICAL POC
9.8
CVE-2011-3544 CRITICAL POC
9.8
CVE-2012-1723 CRITICAL POC
9.8
CVE-2017-10271 HIGH POC
7.5
CVE-2015-1427 CRITICAL POC
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CVE-2025-3248 CRITICAL POC
9.8

Vendor StatusVendor

Ubuntu

Priority: Medium
dovecot
Release Status Version
trusty not-affected code not present
xenial not-affected code not present
bionic not-affected code not present
focal needed -
jammy needed -
noble needed -
questing needed -
upstream released 2.4.3

Debian

dovecot
Release Status Fixed Version Urgency
bullseye vulnerable 1:2.3.13+dfsg1-2+deb11u1 -
bullseye (security) vulnerable 1:2.3.13+dfsg1-2+deb11u2 -
bookworm, bookworm (security) vulnerable 1:2.3.19.1+dfsg1-2.1+deb12u1 -
trixie vulnerable 1:2.4.1+dfsg1-6+deb13u3 -
trixie (security) vulnerable 1:2.4.1+dfsg1-6+deb13u1 -
forky, sid vulnerable 1:2.4.2+dfsg1-4 -
(unstable) fixed (unfixed) -

SUSE

Severity: High
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed
SUSE Linux Enterprise Module for Server Applications 15 SP7 Fixed
SUSE Linux Enterprise Module for Server Applications 15 SP7 Fixed
SUSE Linux Enterprise Server 15 SP7 Fixed

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EUVD-2026-16565 vulnerability details – vuln.today
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