How severe is CVE-2026-40016?

CVE-2026-40016 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with high attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-40016 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (26th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-40016?

CVE-2026-40016 primarily affects Open-xchange Dovecot. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-40016?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-40016 have an EU (EUVD) identifier?

Yes. CVE-2026-40016 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29470.

When was CVE-2026-40016 published?

CVE-2026-40016 was published on 2026-05-12 and last updated on 2026-06-17.

CVE-2026-40016

CVE-2026-40016 is a medium-severity vulnerability in Open-xchange Dovecot with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-400.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
EPSS exploit prediction: 0% (26th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-29470
Weakness: CWE-400
Affected product: Open-xchange Dovecot
Published: 2026-05-12
Last modified: 2026-06-17

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.

Frequently asked questions

What is 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. 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.
How severe is CVE-2026-40016?: CVE-2026-40016 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with high attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-40016 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (26th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-40016?: CVE-2026-40016 primarily affects Open-xchange Dovecot. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-40016?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-40016 have an EU (EUVD) identifier?: Yes. CVE-2026-40016 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29470.
When was CVE-2026-40016 published?: CVE-2026-40016 was published on 2026-05-12 and last updated on 2026-06-17.

References

https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0002.json

Affected products (2)

cpe:2.3:a:dovecot:dovecot:*:*:*:*:*:*:*:*
cpe:2.3:a:open-xchange:dovecot:*:*:*:*:pro:*:*:*

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