Doveadm Anmeldeinformationen werden mit direktem Vergleich verifiziert, was anfällig für einen Timing-Oracle-Angriff ist. Ein Angreifer kann dies nutzen, um die konfigurierten Anmeldeinformationen zu ermitteln. Das Ermitteln der Anmeldeinformationen führt zu vollem Zugriff auf die betroffene Komponente.

The core of this vulnerability lies in how doveadm verifies credentials. Instead of a constant-time comparison, the verification process is susceptible to timing attacks. An attacker can repeatedly attempt different credentials, measuring the time taken for each attempt. By analyzing these timing differences, they can deduce the correct password, even without knowing it directly. Successful exploitation grants the attacker full access to the affected Dovecot Pro component, enabling them to read and modify sensitive data, potentially compromise the entire mail server, and establish a persistent foothold within the environment. While no public exploits are currently known, the potential for credential compromise makes this a significant risk.

Organizations utilizing OX Dovecot Pro in environments with exposed doveadm interfaces are at risk. This includes deployments where the doveadm service is accessible from untrusted networks or where access controls are not properly configured. Shared hosting environments where multiple users share the same server instance are also particularly vulnerable.

• linux / server: Monitor access logs for unusual activity targeting the doveadm HTTP service port (8000). Use ss or lsof to identify connections to this port.

ss -tulnp | grep :8000

• generic web: Use curl to probe the doveadm endpoint and analyze response times for anomalies.

curl -s -w 'Response Time: %{time_total}
' http://<dovecot_pro_ip>:8000/doveadm

1. 2026-03-27Disclosure

   disclosure

1. Reserviert2026-02-24
2. Veröffentlicht2026-03-27
3. EPSS aktualisiert2026-04-03

The primary mitigation for CVE-2026-27856 is to upgrade to a patched version of OX Dovecot Pro. If an immediate upgrade is not feasible due to compatibility concerns or testing requirements, consider implementing temporary workarounds. Restricting access to the doveadm HTTP service port (typically port 8000) can significantly reduce the attack surface. Firewall rules or network segmentation should be employed to limit access to authorized administrators only. Regularly review and audit doveadm access logs for any suspicious activity. After upgrading, confirm the fix by attempting a timing attack against the doveadm interface and verifying that the timing variations are eliminated.