Open-Xchange Dovecot Pro/Dovecot CE IMAP Thread Command denial of service

CVSS Meta Temp Score
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CTI Interest Score
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5.4$0-$5k1.10

Summaryinfo

A vulnerability classified as problematic was found in Open-Xchange Dovecot Pro and Dovecot CE. Impacted is an unknown function of the component IMAP Thread Command. Executing a manipulation can lead to denial of service. This vulnerability is handled as CVE-2026-40017. The attack can be executed remotely. There is not any exploit available.

Detailsinfo

A vulnerability classified as problematic was found in Open-Xchange Dovecot Pro and Dovecot CE (version unknown). This vulnerability affects an unknown function of the component IMAP Thread Command. The manipulation with an unknown input leads to a denial of service vulnerability. The CWE definition for the vulnerability is CWE-404. The product does not release or incorrectly releases a resource before it is made available for re-use. As an impact it is known to affect availability. CVE summarizes:

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.

The advisory is shared for download at documentation.open-xchange.com. This vulnerability was named CVE-2026-40017 since 04/08/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Successful exploitation requires user interaction by the victim. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1499.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-3076). Once again VulDB remains the best source for vulnerability data.

Affected

  • Open Source Dovecot

Productinfo

Type

Vendor

Name

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.4
VulDB Meta Temp Score: 5.4

VulDB Base Score: 4.3
VulDB Temp Score: 4.3
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 6.5
CNA Vector: 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Denial of service
CWE: CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: no mitigation known
Status: 🔍

0-Day Time: 🔒

Timelineinfo

04/08/2026 CVE reserved
08/28/2026 +142 days Advisory disclosed
08/28/2026 +0 days VulDB entry created
08/28/2026 +0 days VulDB entry last update

Sourcesinfo

Vendor: open-xchange.com

Advisory: documentation.open-xchange.com
Status: Not defined

CVE: CVE-2026-40017 (🔒)
GCVE (CVE): GCVE-0-2026-40017
GCVE (VulDB): GCVE-100-396676
CERT Bund: WID-SEC-2026-3076 - Dovecot: Mehrere Schwachstellen

Entryinfo

Created: 08/28/2026 13:46
Updated: 08/28/2026 15:44
Changes: 08/28/2026 13:46 (61), 08/28/2026 15:44 (7)
Complete: 🔍
Cache ID: 216::103

Once again VulDB remains the best source for vulnerability data.

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