RHSA-2026:76763HighCVSS 9.1

Red Hat Security Advisory: dovecot security, bug fix, and enhancement update

Published
October 6, 2026
Last Modified
October 6, 2026

🔗 CVE IDs covered (8)

CVE-2026-33605 →CVE-2026-40018 →CVE-2026-40019 →CVE-2026-42007 →CVE-2026-42391 →CVE-2026-73208 →CVE-2026-27852 →CVE-2026-33263 →

📋 Description

CVE-2026-27852 — dovecot: Dovecot: Denial of service via crafted email headers CVE-2026-33263 — dovecot: Dovecot: Denial of Service and potential message duplication via connection limit exhaustion CVE-2026-33605 — dovecot: Dovecot: Denial of Service in ManageSieve login process CVE-2026-40018 — dovecot: Dovecot: MySQL multi-byte escaping wrong CVE-2026-40019 — dovecot: Dovecot: Denial of Service via truncated quoted argument in ManageSieve CVE-2026-42007 — dovecot: Dovecot: Arbitrary Code Execution via Sieve editheader use-after-free CVE-2026-42391 — dovecot: Dovecot: Denial of Service via IMAP ID command with excessive parameters CVE-2026-73208 — dovecot: Dovecot: Authentication bypass via incorrect OAuth2 token validation

🎯 Affected products70

  • Red Hat Enterprise Linux AppStream (v. 8)
  • Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-1:2.3.16-16.el8_10.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-1:2.3.16-16.el8_10.i686 as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-1:2.3.16-16.el8_10.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-1:2.3.16-16.el8_10.s390x as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-1:2.3.16-16.el8_10.src as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-1:2.3.16-16.el8_10.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-debuginfo-1:2.3.16-16.el8_10.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-debuginfo-1:2.3.16-16.el8_10.aarch64 as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-debuginfo-1:2.3.16-16.el8_10.i686 as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-debuginfo-1:2.3.16-16.el8_10.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-debuginfo-1:2.3.16-16.el8_10.ppc64le as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-debuginfo-1:2.3.16-16.el8_10.s390x as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-debuginfo-1:2.3.16-16.el8_10.s390x as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-debuginfo-1:2.3.16-16.el8_10.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-debuginfo-1:2.3.16-16.el8_10.x86_64 as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-debugsource-1:2.3.16-16.el8_10.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-debugsource-1:2.3.16-16.el8_10.aarch64 as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-debugsource-1:2.3.16-16.el8_10.i686 as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-debugsource-1:2.3.16-16.el8_10.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-debugsource-1:2.3.16-16.el8_10.ppc64le as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-debugsource-1:2.3.16-16.el8_10.s390x as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-debugsource-1:2.3.16-16.el8_10.s390x as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-debugsource-1:2.3.16-16.el8_10.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 8)
  • dovecot-debugsource-1:2.3.16-16.el8_10.x86_64 as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-devel-1:2.3.16-16.el8_10.aarch64 as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-devel-1:2.3.16-16.el8_10.i686 as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-devel-1:2.3.16-16.el8_10.ppc64le as a component of Red Hat Enterprise Linux CRB (v. 8)
  • dovecot-devel-1:2.3.16-16.el8_10.s390x as a component of Red Hat Enterprise Linux CRB (v. 8)
  • +40 more not shown

✅ Remediation

For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Workaround: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability. Workaround: To mitigate this issue, limit the number of connections handled by a single submission-login process. This can be achieved by adjusting the `process_limit` setting for the `submission-login` service in the Dovecot configuration. For example, add or modify the following in a Dovecot configuration file (e.g., `/etc/dovecot/conf.d/10-master.conf`): ``` service submission-login { process_limit = <lower_value> } ``` Reducing this limit may impact performance. After modifying the configuration, restart the Dovecot service for the changes to take effect. Workaround: Restrict network access to the ManageSieve service to trusted clients only. This can be achieved by configuring a firewall to limit incoming connections to the service's port (e.g., 4190 for Sieve) from specific IP addresses or networks. For example, using `firewalld`: ```bash firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="<TRUSTED_IP_OR_NETWORK>" port port="4190" protocol="tcp" accept' firewall-cmd --reload ``` Replace `<TRUSTED_IP_OR_NETWORK>` with the actual trusted source. A firewall reload is required for changes to take effect. Workaround: Restrict network access to the ManageSieve service to trusted clients only. This can be accomplished by configuring a firewall to limit incoming connections to the port used by ManageSieve (typically 4190/tcp) from known, authorized IP addresses or subnets. This action reduces the attack surface by preventing untrusted remote access to the vulnerable service. A service restart or reload may be required for firewall changes to take full effect, depending on the firewall management tool used. Workaround: To mitigate this vulnerability, disable the Sieve `editheader` extension in the Dovecot configuration. After modifying the configuration, the Dovecot service must be restarted for the changes to take effect. Disabling this extension will remove its associated functionality. Workaround: To mitigate this issue, limit the number of connections handled by a single `imap-login` process by adjusting the `process_limit` setting within the `service imap-login` block in your Dovecot configuration (e.g., `/etc/dovecot/dovecot.conf`). Increasing `process_limit` will cause Dovecot to spawn more `imap-login` processes, distributing connections more widely and reducing the impact of a single malicious connection. For example, to set the process limit to 200: ``` # /etc/dovecot/dovecot.conf service imap-login { process_limit = 200 } ``` After modifying the configuration, restart the Dovecot service for the changes to take effect. This may impact performance due to increased process overhead. ```bash systemctl restart dovecot ``` Workaround: To mitigate this issue, ensure that the identity provider issues a scope claim for all tokens used with Dovecot. Additionally, verify that configured scope names in Dovecot do not match audience values from the identity provider. A restart of the Dovecot service may be required for configuration changes to take effect.

🔗 References (12)