high CVSS 7.5 EPSS 0.55%

CVE-2026-40015·Dovecot vulnerability

An attacker that has valid credentials can open many connections to the imap-hibernate service and send invalid commands, which can intermittently cause an out-of-bounds read and crash the process. The crash interrupts hibernated IMAP sessions handled by the affected process, which can cause degradation of service for IMAP. Disable IMAP hibernation. 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 0.55% — higher than 45% 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-2026-40015 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

Organizations running Dovecot should upgrade to version 1:2.4.1+dfsg1-6+deb13u7 or later to resolve this denial-of-service vulnerability affecting the IMAP hibernation service. Authenticated attackers can trigger out-of-bounds memory reads by sending malformed commands, leading to process crashes and service interruptions. As an interim measure, administrators may disable IMAP hibernation if immediate patching is not feasible, though upgrading is the recommended long-term solution.

sudo dnf update dovecot

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

Multiple rapid IMAP hibernation service connection attempts followed by invalid IMAP protocol commands (e.g., non-RFC-compliant sequences) correlating with imap-hibernate process termination or segmentation faults in logs within seconds of command receipt.

How to check if you are affected

  1. Check installed Dovecot version: dovecot --version or dpkg -l | grep dovecot
  2. Verify if IMAP hibernation is enabled: grep -i 'imap_hibernation' /etc/dovecot/dovecot.conf (enabled by default)
  3. Monitor for imap-hibernate process crashes in system logs: journalctl -u dovecot | grep -i 'crash\|segfault\|terminated' or tail -f /var/log/mail.log
  4. Confirm patch application by re-running dovecot --version and verifying version matches 1:2.4.1+dfsg1-6+deb13u7 or later, then restart Dovecot: sudo systemctl restart dovecot

FAQ

What is CVE-2026-40015?

CVE-2026-40015 is a denial-of-service vulnerability in Dovecot's IMAP hibernation service that allows authenticated users to crash the process by sending invalid commands, resulting in temporary service interruption for hibernated IMAP sessions.

Is CVE-2026-40015 being actively exploited?

No, this vulnerability is not currently being exploited in the wild according to CISA's Known Exploited Vulnerabilities catalog, and no public exploit code is available.

What versions of Dovecot are affected by CVE-2026-40015?

All versions prior to 1:2.4.1+dfsg1-6+deb13u7 are affected; the exact initial affected version is unknown, but Debian-based systems should ensure they are running the patched version or later.

How do I check if my server is vulnerable to CVE-2026-40015?

Run 'dovecot --version' and compare output against version 1:2.4.1+dfsg1-6+deb13u7; if your version is older, your system is vulnerable. Additionally, confirm IMAP hibernation is enabled with 'grep imap_hibernation /etc/dovecot/dovecot.conf'.

Does Defensia detect CVE-2026-40015?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Dovecot is installed on a monitored server, CVE-2026-40015 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

Track CVEs across your fleet automatically

Defensia scans your Linux servers and tells you exactly which ones are running vulnerable versions — including CVE-2026-40015. Free for 1 server.

Get started free