High [CVE-2026-40019] Denial of Service via truncated quoted argument in ManageSieve
This high-severity Red Hat Linux advisory covers CVE-2026-40019 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 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.
This action causes the process to enter an infinite loop, consuming excessive CPU resources. 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-835. 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 1 hour 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 1 hour ago·verify at source
Mitigation checklist
- 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.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
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