CVE-2026-27857 Denial of service in OX Dovecot Pro
An attacker can cause a denial of service by sending crafted NOOP commands that exhaust server memory, requiring an upgrade to the fixed version.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-27857?
CVE-2026-27857 is a medium-severity denial of service vulnerability in Dovecot Dovecot, published on 27 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Sending "NOOP (((...)))" command with 4000 parenthesis open+close results in ~1MB extra memory usage. Longer commands will result in client disconnection. This 1 MB can be left allocated for longer time periods by not sending the command ending LF. So attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Attacker could connect possibly from even a single IP and create 1000 connections to allocate 1 GB of memory, which would likely result in reaching VSZ limit and killing the process and its other proxied connections. Install fixed version, there is no other remediation. No publicly available exploits are known.
Which versions are affected by CVE-2026-27857?
It affects 2 products.
Products include Dovecot Dovecot, Open-Xchange Dovecot.
How do I fix CVE-2026-27857?
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-2026-27857 being exploited?
There is no known exploitation of CVE-2026-27857 in the wild and no public exploit code.
Other vulnerabilities in Dovecot Dovecot
Sources
Also known as ALPINE-CVE-2026-27857, AZL-81707, CLSA-2026-1777976700, CLSA-2026-1777977059, CLSA-2026-1777978787, CLSA-2026-1778022490 and 8 more.