CVE-2026-61911: An issue was discovered in Cyrus IMAP before 3.12.4

Routine

MEDIUM 4.3UPGRADE

CVE-2026-61911 is a medium-severity flaw (CVSS 4.3) affecting imap. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 88%)
CISA exploited list	No
Weakness	CWE-497
Published	2026-09-09
Last modified	2026-09-16

Publisher (CNA): MITRE · Vendor: cyrus

Last updated 2026-09-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-09 20:18 UTCPublished CVE record published
2026-09-16 15:23 UTCUpdated Record last modified

cyrus imap UPGRADE

Affected: < 3.8.8 · >= 3.9.0 and < 3.10.4 · >= 3.11.0 and < 3.12.4

Fixed in: 3.8.8, 3.10.4, 3.12.4

Safe to downgrade to: a release before 3.9.0

1. Check installed version

apt-cache policy imap || rpm -q imap || imap --version

2. UPGRADE to 3.8.8 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade imap

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade imap

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 3.9.0 (Debian / Ubuntu)

apt-cache madison imap sudo apt install imap=<VERSION_BEFORE_3.9.0> sudo apt-mark hold imap

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list imap sudo dnf downgrade imap-<VERSION_BEFORE_3.9.0> sudo dnf versionlock add imap

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-61911?

imap: upgrade to 3.8.8, 3.10.4, 3.12.4. Exact commands for each OS are on this page.

Is CVE-2026-61911 being exploited?

CVE-2026-61911 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-61911 affect?

CVE-2026-61911 affects imap. Severity is medium (CVSS 4.3). 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 mailb

How urgent is CVE-2026-61911?

Priority 18/100. No elevated risk signals yet.

Related CVEs

CVE-2026-61908 LOW 3.1 UPGRADE An issue was discovered in Cyrus IMAP before 3.12.4
CVE-2026-61909 LOW 3.5 UPGRADE An issue was discovered in Cyrus IMAP before 3.12.4
CVE-2026-61910 LOW 3.5 UPGRADE An issue was discovered in Cyrus IMAP before 3.12.4
CVE-2026-61915 MEDIUM 4.2 UPGRADE An issue was discovered in Cyrus IMAP before 3.12.4

References

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