high CVSS 7 EPSS 0.17%

CVE-2026-42393·Dovecot vulnerability

The comparison used for the doveadm password and API key is not fully timing safe and can reveal the length of the configured secret. An attacker with access to the same network as the doveadm service, able to make repeated requests and measure response timing accurately, can learn the length of the secret, which reduces the effort needed to guess it. The secret value itself is not disclosed. Restrict network access to the doveadm service to trusted clients. 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 0.17% — higher than 6% 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-2026-42393 scores 7 on CVSS, so a successful attack would be serious — but at 0.17%, 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's doveadm password and API key comparison function is vulnerable to timing-based side-channel attacks that can leak the length of configured secrets. Upgrade to version 1:2.4.1+dfsg1-6+deb13u7 or later to remediate this vulnerability. Additionally, restrict network access to the doveadm service to only trusted administrative clients to minimize exposure during any interim patching window.

sudo dnf update dovecot

Defensia detects this vulnerability

How to check if you are affected

  1. Run `dovecot --version` to identify the currently installed Dovecot release
  2. Check if doveadm is exposed on the network by running `sudo netstat -tlnp | grep doveadm` or `sudo ss -tlnp | grep doveadm`
  3. Review `/etc/dovecot/dovecot.conf` for the `doveadm_port` and `doveadm_password` settings to confirm if password-based authentication is configured
  4. After patching, re-run `dovecot --version` and confirm the version matches or exceeds 1:2.4.1+dfsg1-6+deb13u7

FAQ

What is CVE-2026-42393?

CVE-2026-42393 is a timing side-channel vulnerability in Dovecot's doveadm service where the password and API key comparison function does not use fully constant-time operations, allowing attackers on the same network to infer the length of the configured secret through repeated timing measurements.

Is CVE-2026-42393 being actively exploited?

No, CVE-2026-42393 is not listed on the CISA KEV catalog and no public exploits are currently known. However, the vulnerability requires only network access and basic timing measurement capabilities, making it a potential future target.

What versions of Dovecot are affected by CVE-2026-42393?

All Dovecot versions up to and including 1:2.4.1+dfsg1-6+deb13u6 are affected. The vulnerability is patched in version 1:2.4.1+dfsg1-6+deb13u7 and later.

How do I check if my server is vulnerable to CVE-2026-42393?

Run `dovecot --version` and compare the output against version 1:2.4.1+dfsg1-6+deb13u7. If your version is older, your system is vulnerable. Additionally, check if doveadm is exposed on the network using `sudo ss -tlnp | grep doveadm`.

Does Defensia detect CVE-2026-42393?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Dovecot is installed on a monitored server, CVE-2026-42393 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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