high CVSS 7.5 EPSS 0.55%

CVE-2026-33607·Dovecot vulnerability

An attacker that has valid credentials can use IMAP LIST command to consume CPU. This can cause degradation or denial of service for IMAP. Monitor system for abnormal CPU usage and kill the offending process and lock account. Alternatively install fixed 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 0.55% — higher than 44% 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-2026-33607 scores 7.5 on CVSS, so a successful attack would be serious — but at 0.55%, 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

Update Dovecot to version 1:2.4.1+dfsg1-6+deb13u7 or later to resolve a resource exhaustion vulnerability in the IMAP LIST command handler. Authenticated attackers can trigger excessive CPU consumption by sending specially crafted LIST commands, potentially degrading mail service availability. Prioritize this update for mail servers exposed to untrusted network access or with high user counts.

sudo dnf update dovecot

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

Multiple IMAP LIST commands from single authenticated session within short time interval (e.g., >50 LIST commands per minute) correlating with elevated dovecot process CPU usage >80%. Pattern: LIST.*LIST.*LIST in rapid succession in imap.log

How to check if you are affected

  1. Check installed Dovecot version: dovecot --version or dpkg -l | grep dovecot
  2. Verify IMAP service is running and exposed: netstat -tlnp | grep :143 or ss -tlnp | grep :143
  3. Search Dovecot logs for repeated LIST commands from single user: grep -i 'LIST' /var/log/dovecot/imap.log | awk '{print $NF}' | sort | uniq -c | sort -rn
  4. Confirm patch applied: dpkg -l dovecot-core | grep 2.4.1+dfsg1-6+deb13u7

FAQ

What is CVE-2026-33607?

A denial-of-service vulnerability in Dovecot's IMAP implementation where authenticated users can craft LIST commands that consume excessive CPU resources, degrading or disabling IMAP service for all users on the affected mail server.

Is CVE-2026-33607 being actively exploited?

No, this vulnerability is not listed on CISA's Known Exploited Vulnerabilities (KEV) catalog, and no public exploits are currently available.

What versions of Dovecot are affected by CVE-2026-33607?

Dovecot versions prior to 1:2.4.1+dfsg1-6+deb13u7 on Debian 13 are vulnerable. Administrators should verify their specific distribution's patched version via their package management system.

How do I check if my server is vulnerable to CVE-2026-33607?

Run 'dovecot --version' and compare against the patched version for your distribution. If your version is older than the fix, your system is vulnerable and requires immediate patching.

Does Defensia detect CVE-2026-33607?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Dovecot is installed on a monitored server, CVE-2026-33607 will appear in your dashboard with remediation steps.

Related Dovecot CVEs

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-2026-40018CVSS 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-2026-27852CVSS 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-2026-73208CVSS 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.

References

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