CVE-2026-33605 Denial of service in OX Dovecot CE
An unauthenticated attacker can cause a denial of service in ManageSieve by sending malformed commands, particularly affecting high-performance mode configurations.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33605?
CVE-2026-33605 is a high-severity denial of service vulnerability in Open-Xchange GmbH OX Dovecot CE, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-400
Which versions are affected by CVE-2026-33605?
How do I fix CVE-2026-33605?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-33605 being exploited?
There is no known exploitation of CVE-2026-33605 in the wild and no public exploit code.
Sources
Also known as ALPINE-CVE-2026-33605, AZL-98259, DEBIAN-CVE-2026-33605, GHSA-j4m8-9jmg-4wpv, UBUNTU-CVE-2026-33605.