CVE-2026-61911: Cyrus IMAP Cyrus IMAP vulnerability
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 Software
Event History
Frequently Asked Questions
Who can exploit this issue?
An authenticated Cyrus IMAP user who can install a Sieve script can exploit the oracle during LMTP delivery.
What information could an attacker obtain?
The attacker could determine whether another user's private mailbox exists. They could also read the value of shared mailbox annotations by observing which fileinto branch is taken.
Which deployments are affected?
Cyrus IMAP versions before 3.12.4 are affected. The provided information does not state whether any particular default Sieve or LMTP configuration is required beyond the ability to install a Sieve script and observe LMTP delivery behavior.