Medium severity · published May 12, 2026
CVE-2026-40016
Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU time limits for Sieve up to 130 times of the configured limit
6.5
CVSS
0.3%
EPSS
No
On KEV
Description
Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or alternatively prevent direct access to Sieve scripts via ManageSieve or local access. No publicly available exploits are known.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
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 Pro · Open-Xchange GmbH
through 2.3.0 · source: vendor
DO
Dovecot · Dovecot
before 2.4.4 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-40016
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-40016
Vendor Advisory
https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0002.json
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