CVE-2025-59028

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-27 · updated 2026-10-07
Weakness: CWE-20

Description

When sending invalid base64 SASL data, login process is disconnected from the auth server, causing all active authentication sessions to fail. Invalid BASE64 data can be used to DoS a vulnerable server to break concurrent logins. Install fixed version or disable concurrency in login processes (heavy perfomance penalty on large deployments). No publicly available exploits are known.

Affected products

dovecot: before 2.4.3 — fixed in 2.4.3
Open-Xchange Dovecot: before 3.1.2 — fixed in 3.1.2

How to fix

Upgrade to a fixed version: dovecot 2.4.3; Open-Xchange Dovecot 3.1.2. Check the vendor advisory for mitigations.

References

https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0001.json

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