high CVSS 7.5 EPSS 0.30%

CVE-2026-52681·Dovecot vulnerability

Sieve CPU resource usage is tracked in the compiled script, so an attacker that has valid credentials can reset the accounting by repeatedly changing the active script. Compiled script files are also not removed when a script is deleted or renamed. The configured Sieve CPU limit can be bypassed, allowing sustained CPU consumption, and the leftover files increase disk consumption. Both can cause degradation of service for mail delivery. Monitor system for abnormal CPU usage and disk consumption. Update to non-vulnerable version. No publicly available exploits are known.

Severity
high
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 0.30% — higher than 20% 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-2026-52681 scores 7.5 on CVSS, so a successful attack would be serious — but at 0.30%, 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

Upgrade Dovecot to version 1:2.4.1+dfsg1-6+deb13u7 or later to address a resource accounting bypass in the Sieve mail filtering subsystem. This vulnerability allows authenticated attackers to circumvent CPU limits and accumulate orphaned compiled script files, potentially degrading mail delivery performance. Apply the patch immediately and monitor your system for unusual CPU and disk usage patterns during the transition.

sudo dnf update dovecot

Defensia detects this vulnerability

How to check if you are affected

  1. Run `dovecot --version` to display the currently installed Dovecot version and compare it against 1:2.4.1+dfsg1-6+deb13u7
  2. Verify Sieve support is enabled by checking if the sieve and sieve_global plugins are loaded in `/etc/dovecot/conf.d/90-sieve.conf`
  3. Search your Sieve script directory (typically `/var/lib/dovecot/sieve/`) for orphaned `.svbin` compiled script files that lack corresponding `.sieve` source files using `find /var/lib/dovecot/sieve/ -name '*.svbin' -type f`
  4. After patching, confirm the new version with `dovecot --version` and restart the Dovecot service using `sudo systemctl restart dovecot`

FAQ

What is CVE-2026-52681?

This vulnerability exists in Dovecot's Sieve mail filtering engine, where the CPU resource accounting mechanism can be reset by repeatedly modifying the active Sieve script. Additionally, compiled script binaries are not cleaned up when scripts are deleted, allowing an authenticated user to exhaust CPU and disk resources.

Is CVE-2026-52681 being actively exploited?

No. This CVE is not listed on CISA's Known Exploited Vulnerabilities catalog, and no public exploits are currently available. However, any user with valid mail account credentials can exploit this vulnerability.

What versions of Dovecot are affected by CVE-2026-52681?

All Dovecot versions up to and including 1:2.4.1+dfsg1-6+deb13u6 are affected. The fix was introduced in version 1:2.4.1+dfsg1-6+deb13u7.

How do I check if my server is vulnerable to CVE-2026-52681?

Run `dpkg -l | grep dovecot` on Debian/Ubuntu systems or `rpm -qa dovecot` on RHEL/CentOS, then compare the version against 1:2.4.1+dfsg1-6+deb13u7. If your version is older, you are vulnerable.

Does Defensia detect CVE-2026-52681?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Dovecot is installed on a monitored server, CVE-2026-52681 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-2026-40018CVSS 9None None None 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-2026-42391CVSS 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

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