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OX Dovecot CVE-2026-40017

| EUVDEUVD-2026-67666 MEDIUM
Uncontrolled Resource Consumption (CWE-400)
2026-08-28 OX GHSA-gr5f-599w-cg8j
Denial Of Service Red Hat Ox Dovecot Pro Ox Dovecot Ce Open Xchange Gmbh
6.5
CVSS 3.1 · Vendor: OX
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Severity by source

Vendor (OX) PRIMARY
6.5 MEDIUM
AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
vuln.today AI
6.5 MEDIUM

Attacker sends mail over network (AV:N, PR:N), low crafting complexity (AC:L), but THREAD command by mail client is required (UI:R); impact is availability-only with no scope change.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
MEDIUM
qualitative
Red Hat
6.5 MEDIUM
qualitative

Primary rating from Vendor (OX).

CVSS VectorVendor: OX

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

2
Patch available
Aug 28, 2026 - 13:17 EUVD
Analysis Generated
Aug 28, 2026 - 12:13 vuln.today

DescriptionCVE.org

An attacker that can send mail to a user can craft a message header whose values are chosen to collide in an internal hash table, which makes the IMAP THREAD command consume CPU disproportionate to the size of the message. This is a separate issue from CVE-2026-40014 and is not addressed by that fix. Whenever a mail client issues a THREAD command on the affected mailbox, this can cause degradation or denial of service for IMAP. Monitor system for abnormal CPU usage, kill the offending process and remove the offending message from the affected mailbox. Update to non-vulnerable version. No publicly available exploits are known.

AnalysisAI

OX Dovecot Pro and OX Dovecot CE are susceptible to a hash-collision denial-of-service attack where an attacker who can deliver mail to a target user can craft message headers engineered to collide in an internal hash table, causing the IMAP THREAD command to consume CPU disproportionate to message size. Any mail client issuing THREAD against the poisoned mailbox triggers sustained CPU exhaustion, degrading or denying IMAP service. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Delivery
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Exploit
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Execution
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Vulnerability AssessmentAI

Exploitation The attacker must be able to deliver email to a mailbox hosted on a vulnerable OX Dovecot instance - standard mail delivery capability, requiring no authentication to the IMAP server itself. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 6.5 medium score is well-calibrated for this vulnerability. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Update to a non-vulnerable version of OX Dovecot Pro or OX Dovecot CE as directed by the vendor advisory at https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0003.json; the exact patched version number is not independently confirmed from available data and should be obtained directly from the advisory. … Detailed patch versions, workarounds, and compensating controls in full report.
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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise High Performance Computing 12 Affected
SUSE Linux Enterprise High Performance Computing 12 Affected
SUSE Linux Enterprise Module for Server Applications 15 SP7 Affected
SUSE Linux Enterprise Module for Server Applications 15 SP7 Affected

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CVE-2026-40017 vulnerability details – vuln.today
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