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CVE-2026-42391

HIGHCVSS 7.5/10EPSS 0.38%

Last modified

CVE-2026-42391 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. EPSS estimates a 0.38% chance of exploitation in the next 30 days.

Description

An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.

Metrics

CVSS 3.1
7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability
0.38%

30.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
Open-Xchange GmbHOX Dovecot Pro>= 2.3.0, < 2.3.22.2; >= 3.0.0, < 3.0.7; >= 3.1.0, < 3.1.6
Open-Xchange GmbHOX Dovecot CE>= 2.3.0, < 2.4.5

References

Timeline

Published
Last Modified
Status
Deferred

Frequently Asked Questions

What is CVE-2026-42391?
An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.
How severe is CVE-2026-42391?
CVE-2026-42391 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.38% probability of exploitation in the next 30 days.
How do I fix CVE-2026-42391?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST