High [CVE-2026-33605] Denial of Service in ManageSieve login process
This high-severity Red Hat Linux advisory covers CVE-2026-33605 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7.
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Summary
An 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. A flaw was found in Dovecot.
Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-1286.
Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9. Will not fix / out of support: Red Hat Enterprise Linux 6.
Red Hat does not currently list a fixing RHSA for this CVE.
Affected products named by the advisory: Red Hat package: dovecot.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
Mitigation checklist
- 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.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
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