critical CVSS 9 EPSS 0.32%

CVE-2026-40018·Dovecot vulnerability

None None None No publicly available exploits are known.

Severity
critical
Software
Dovecot
Fixed in
1:2.4.1+dfsg1-6+deb13u7
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 0.32% — higher than 23% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2026-40018 scores 9 on CVSS, so a successful attack would be serious — but at 0.32%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

Until: 1:2.4.1+dfsg1-6+deb13u7

Fixed in: 1:2.4.1+dfsg1-6+deb13u7

How to fix this CVE

Dovecot versions prior to 1:2.4.1+dfsg1-6+deb13u7 contain a critical vulnerability that could compromise mail server confidentiality and integrity. Administrators should prioritize upgrading to version 1:2.4.1+dfsg1-6+deb13u7 or later immediately. After patching, restart the Dovecot service and verify the update through package management tools.

sudo dnf update dovecot && sudo systemctl restart dovecot

Defensia detects this vulnerability

How to check if you are affected

  1. Run `dovecot --version` to check the currently installed Dovecot version on your system
  2. Cross-reference the output against the vulnerable range (versions before 1:2.4.1+dfsg1-6+deb13u7); if your version is lower, the server is vulnerable
  3. Check Dovecot logs at `/var/log/dovecot/dovecot.log` and `/var/log/dovecot/info.log` for any unusual authentication failures or protocol violations that may indicate exploitation attempts
  4. After applying the patch, re-run `dovecot --version` and confirm the version matches or exceeds 1:2.4.1+dfsg1-6+deb13u7, then verify Dovecot is running with `sudo systemctl status dovecot`

FAQ

What is CVE-2026-40018?

CVE-2026-40018 is a critical vulnerability in Dovecot mail server that affects the confidentiality and integrity of email communications. It requires network access to trigger but does not require user interaction or elevated privileges.

Is CVE-2026-40018 being actively exploited?

No, CVE-2026-40018 is not currently listed in the CISA Known Exploited Vulnerabilities catalog, and no public exploit code is available, though this does not eliminate the risk of future exploitation.

What versions of Dovecot are affected by CVE-2026-40018?

All Dovecot versions up to and including 1:2.4.1+dfsg1-6+deb13u6 are vulnerable; version 1:2.4.1+dfsg1-6+deb13u7 and later contain the fix.

How do I check if my server is vulnerable to CVE-2026-40018?

Execute `dpkg -l | grep dovecot` on Debian/Ubuntu systems or `rpm -qa | grep dovecot` on RHEL-based systems, then compare the output version against 1:2.4.1+dfsg1-6+deb13u7 to determine if your installation is vulnerable.

Does Defensia detect CVE-2026-40018?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Dovecot is installed on a monitored server, CVE-2026-40018 will appear in your dashboard with remediation steps.

Related Dovecot CVEs

CVE-2026-73208CVSS 9An attacker that holds a token intended for a different purpose can authenticate, because when an OAuth2 token response does not contain a scope claim, the audience claim is used in its place and checked against the configured required scopes. These are different concepts, and the audience claim does not describe what a token is allowed to do. A token that grants no relevant permissions can be accepted because its intended recipient value happens to match a configured scope name, granting access that should have been denied. It also hides an identity provider misconfiguration where scopes are not being issued at all. Ensure the identity provider issues a scope claim for all tokens used with Dovecot, and that configured scope names do not match audience values. Update to non-vulnerable version. No publicly available exploits are known.
CVE-2026-40019CVSS 9An unauthenticated attacker can send a truncated quoted argument to the ManageSieve login process, which makes it spin in an infinite loop consuming CPU. This can cause degradation or denial of service for Sieve script management, and repeated connections can consume all available CPU on the server. Monitor system for abnormal CPU usage and kill the offending process. Restrict network access to the ManageSieve service to trusted clients. Update to non-vulnerable version. No publicly available exploits are known.
CVE-2026-33605CVSS 9An unauthenticated attacker can crash the ManageSieve login process by sending a small malformed command before authenticating. If running in high-security mode (default for community releases), only the attacker's own connection is terminated. If running in high-performance mode (default for Pro releases), all connections handled by the same managesieve-login process are terminated. Repeating the attack can cause denial of service for Sieve script management. Restrict network access to the ManageSieve service to trusted clients. Update to non-vulnerable version. No publicly available exploits are known.
CVE-2026-27852CVSS 9An attacker that can send mail to a user can craft a message whose headers contain a very large number of email addresses or MIME parameters, which causes excessive memory usage when the message is later parsed. The message is still delivered, but reading it over IMAP can exhaust the memory limit of the process and terminate it, causing denial of service for the affected user. Update to non-vulnerable version. No publicly available exploits are known.
CVE-2026-42391CVSS 9An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.

References

Track CVEs across your fleet automatically

Defensia scans your Linux servers and tells you exactly which ones are running vulnerable versions — including CVE-2026-40018. Free for 1 server.

Get started free