CVE-2026-61911

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-09 · updated 2026-09-16
Weakness: CWE-497

Description

An issue was discovered in Cyrus IMAP before 3.12.4. There is a Sieve mailbox existence oracle. An authenticated user could install a Sieve script that probed whether another user's private mailbox existed, or read the value of shared mailbox annotations, by observing which fileinto branch fired during LMTP delivery.

Affected products

cyrusimap Cyrus IMAP: before 3.8.8; from 3.9.0 before 3.10.4; from 3.11.0 before 3.12.4 — fixed in 3.10.4, 3.12.4, 3.8.8

How to fix

Upgrade to a fixed version: cyrusimap Cyrus IMAP 3.10.4, 3.12.4, 3.8.8. Check the vendor advisory for mitigations.

References

https://cyrusimap.org
https://www.cyrusimap.org/3.12/imap/download/release-notes/3.10/x/3.10.4.html
https://www.cyrusimap.org/3.12/imap/download/release-notes/3.12/x/3.12.4.html
https://www.cyrusimap.org/3.12/imap/download/release-notes/3.8/x/3.8.8.html

Get alerted when CVE-2026-61911 or the next vulnerability affects your stack