Medium severity · published Aug 28, 2026
CVE-2026-40017
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…
6.5
CVSS
0.3%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 27% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
OD
OX Dovecot CE · Open-Xchange GmbH
2.3.0 before 2.4.5 · source: vendor
OD
OX Dovecot Pro · Open-Xchange GmbH
2.3.0 before 2.3.22.2; 3.0.0 before 3.0.7; 3.1.0 before 3.1.6 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-40017
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-40017
documentation.open-xchange.com
https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0003.json
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