high CVSS 7.5 EPSS 0.25%

CVE-2026-33606·Dovecot vulnerability

Mail content stored by a user can be crafted so that it is interpreted as dsync protocol commands when an administrator later runs dsync with the stream protocol, for example during a migration. Injected commands can modify mailbox state on the destination during migration or replication, including internal mailbox attributes that a user should not be able to set directly. It can also cause dsync errors. Avoid running dsync with the stream protocol on mailboxes with untrusted content. 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 0.25% — higher than 14% 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-2026-33606 scores 7.5 on CVSS, so a successful attack would be serious — but at 0.25%, 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 administrators should update to version 1:2.4.1+dfsg1-6+deb13u7 or later to eliminate the dsync protocol injection vulnerability. This vulnerability allows attackers to craft malicious mail content that executes as dsync commands during migration or replication operations, potentially compromising mailbox integrity. Immediately patch all Dovecot installations and avoid running dsync operations on mailboxes containing untrusted content until patching is complete.

sudo dnf install dovecot dovecot-pigeonhole && sudo systemctl restart dovecot

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check installed Dovecot version with: dovecot --version
  2. Step 2: Confirm if dsync is enabled and configured for stream protocol: grep -r 'dsync' /etc/dovecot/ | grep -i stream
  3. Step 3: Search Dovecot logs for dsync errors or unexpected mailbox state changes: grep -i 'dsync' /var/log/dovecot/dovecot.log | grep -E '(error|failed|invalid)'
  4. Step 4: Verify the patch by running: dpkg -l | grep dovecot and confirming version is 1:2.4.1+dfsg1-6+deb13u7 or higher

FAQ

What is CVE-2026-33606?

CVE-2026-33606 is a mail content injection vulnerability in Dovecot that allows attackers to embed dsync protocol commands within email messages, which are then executed during administrative migration or replication tasks, potentially altering mailbox state and internal attributes.

Is CVE-2026-33606 being actively exploited?

No, CVE-2026-33606 is not currently listed on the CISA KEV catalog and no public exploits are documented. However, the vulnerability requires deliberate administrative action (running dsync with stream protocol), making it primarily a risk in migration scenarios.

What versions of Dovecot are affected by CVE-2026-33606?

All Dovecot versions prior to 1:2.4.1+dfsg1-6+deb13u7 are affected. The vulnerability exists in all versions up to and including 1:2.4.1+dfsg1-6+deb13u6 on Debian-based systems.

How do I check if my server is vulnerable to CVE-2026-33606?

Run: dovecot --version and compare the output to 1:2.4.1+dfsg1-6+deb13u7. If your version is lower, your system is vulnerable. Additionally, check if dsync is configured: dovecot -c /etc/dovecot/dovecot.conf -a

Does Defensia detect CVE-2026-33606?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Dovecot is installed on a monitored server, CVE-2026-33606 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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