Angreifer kann eine speziell gestaltete Nachricht vor der Authentifizierung senden, die dazu führt, dass managesieve eine große Menge an Speicher zuweist. Angreifer kann dazu bringen, dass managesieve-login durch wiederholtes Abstürzen des Prozesses nicht verfügbar ist.

The primary impact of CVE-2026-27858 is a denial-of-service condition. An attacker can repeatedly crash the managesieve process by sending malicious messages, rendering it unavailable to legitimate users. This can disrupt email management tasks and potentially impact business operations. While the vulnerability doesn't directly lead to data exfiltration or remote code execution, the disruption caused by the DoS can be significant. The ability to repeatedly crash the process suggests a potential for resource exhaustion and broader system instability if not addressed.

Organizations relying on Dovecot Pro managesieve for email management, particularly those with publicly accessible managesieve endpoints, are at risk. Environments with legacy configurations or those lacking robust access controls are especially vulnerable.

• linux / server:

journalctl -u dovecot -f | grep -i 'managesieve-login' -i 'memory allocation'

• linux / server:

ps aux | grep managesieve-login | grep -v grep | awk '{print $6}' | sort -n | tail -1

• generic web: Monitor system memory usage for unusual spikes, particularly related to the dovecot process.

1. 2026-03-27Disclosure

   disclosure

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

The recommended mitigation for CVE-2026-27858 is to upgrade to a patched version of OX Dovecot Pro. Until an upgrade is possible, restrict access to the managesieve protocol to trusted users and systems. Implement rate limiting on incoming managesieve connections to prevent an attacker from overwhelming the system with malicious requests. Consider deploying a Web Application Firewall (WAF) or proxy to filter potentially malicious messages before they reach the managesieve server. After upgrading, confirm the fix by attempting to trigger the vulnerability with a crafted message and verifying that the process remains stable.