high CVSS 7.4 EPSS 0.58%

CVE-2026-27851·Dovecot vulnerability

When safe filter is used with variable expansion, all following pipelines on the same string are incorrectly interpreted as safe too, enabling unsafe data to be unescaped. This can enable SQL / LDAP injection attacks when used in authentication. Avoid using safe filter until on fixed version. No publicly available exploits are known.

Severity
high
Software
Dovecot
Fixed in
2.4.4
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 0.58% — higher than 46% 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-2026-27851 scores 7.4 on CVSS, so a successful attack would be serious — but at 0.58%, 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: 2.4.4

Fixed in: 2.4.4

How to fix this CVE

Update Dovecot to version 2.4.4 or later to patch the unsafe filter variable expansion flaw that can lead to SQL and LDAP injection in authentication mechanisms. Organizations using the safe filter in Dovecot configurations should prioritize this update immediately, as the vulnerability allows downstream pipelines to incorrectly process unsafe data. Review your Dovecot filter configurations after patching to ensure no reliance on the previous unsafe behavior.

sudo dnf update dovecot

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed Dovecot version: dovecot --version | grep -oP '\d+\.\d+\.\d+'
  2. Verify if safe filter is enabled in configuration: grep -r 'safe' /etc/dovecot/conf.d/ | grep -i filter
  3. Search Dovecot logs for authentication attempts with variable expansion patterns: grep -E 'sieve.*\$|safe.*\|' /var/log/dovecot/dovecot.log
  4. Confirm patch applied by re-running dovecot --version and verifying it reports 2.4.4 or higher

FAQ

What is CVE-2026-27851?

CVE-2026-27851 is a critical filter processing flaw in Dovecot that causes the safe filter to incorrectly mark subsequent pipelines as safe when variable expansion is used, potentially allowing injection of unsanitized data into SQL and LDAP queries during user authentication.

Is CVE-2026-27851 being actively exploited?

No, CVE-2026-27851 is not currently listed on the CISA Known Exploited Vulnerabilities catalog, and no public exploits are documented; however, this does not diminish the need for immediate patching given the injection attack surface.

What versions of Dovecot are affected by CVE-2026-27851?

All Dovecot versions up to and including 2.4.3 are affected; version 2.4.4 and later contain the fix.

How do I check if my server is vulnerable to CVE-2026-27851?

Run 'dovecot --version' and confirm the version is 2.4.4 or later. Additionally, check if the safe filter is actively used in /etc/dovecot/conf.d/*.conf with 'grep -r "safe" /etc/dovecot/conf.d/' to determine if your configuration triggers the vulnerable code path.

Does Defensia detect CVE-2026-27851?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Dovecot is installed on a monitored server, CVE-2026-27851 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-2026-27852CVSS 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.

References

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