Is CVE-2026-61911 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-61911 being exploited in the wild.

How severe is CVE-2026-61911?

Medium severity, with a CVSS score of 4.3, published 9 September 2026.

Is there a fix for CVE-2026-61911?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-61911 attacked?

It is attacked over the network, in a hosted service.

Am I affected by CVE-2026-61911?

Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-61911: Cyrus IMAP Sieve mailbox existence oracle

CVE-2026-61911 · Severity: medium · CVSS 4.3 · Published 2026-09-09

Cyrus IMAP is an email and calendar server used in production environments worldwide. An authenticated user can exploit a flaw in Sieve mail filtering to probe whether other users' private mailboxes exist or read shared mailbox settings by observing how mail delivery behaves, potentially exposing sensitive organizational structure information.

Quick answers

Is CVE-2026-61911 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-61911 being exploited in the wild.
How severe is CVE-2026-61911?: Medium severity, with a CVSS score of 4.3, published 9 September 2026.
Which products and versions are affected?: Cyrus IMAP before 3.12.4.
Is there a fix for CVE-2026-61911?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-61911 attacked?: It is attacked over the network, in a hosted service.
Am I affected by CVE-2026-61911?: Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability is an information disclosure flaw in Cyrus IMAP's Sieve mail filtering implementation. An authenticated user can craft a Sieve script with fileinto branches to different mailbox names and observe which branch fires during LMTP delivery, allowing them to deduce whether another user's private mailbox exists or read shared mailbox annotations. The attack requires authentication but no special privileges beyond the ability to install Sieve scripts. An attacker can map out the mailbox structure and shared configuration of other users. The vulnerability was fixed in version 3.12.4.

Affected products

Cyrus IMAP before 3.12.4

Timeline

2026-09-09: disclosed

References

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