CVE-2026-50055 Zimbra CVE debrief

Who should care

Defenders responsible for configuring and monitoring Zimbra Collaboration Suite should assess exposure and verify mail forwarding restrictions.

Why it matters

Defenders should prioritize verifying mail forwarding restrictions and monitoring Sieve notify actions to prevent unauthorized email forwarding and potential malicious activity.

• Verify mail forwarding restrictions to prevent unauthorized email forwarding
• Monitor Sieve notify actions to detect potential malicious activity
• Review email content and header filtering rules to prevent sensitive information disclosure

Technical summary

The policy-enforcement flaw in Zimbra Collaboration Suite allows an authenticated user to bypass disabled mail forwarding by using a Sieve notify action to send copies of email content and headers to an arbitrary address. This issue affects mail forwarding configurations and requires verification of Sieve notify actions to prevent unauthorized email forwarding. The flaw is related to the Sieve notify action and its interaction with mail forwarding restrictions.

Defensive priority

Defenders should prioritize verifying mail forwarding restrictions and monitoring Sieve notify actions.

Recommended defensive actions

• Verify mail forwarding restrictions are properly configured
• Monitor Sieve notify actions for suspicious activity
• Review and update email content and header filtering rules

Evidence notes

The CVE Program record and NVD vulnerability detail provide official information about the policy-enforcement flaw in Zimbra Collaboration Suite. The source item provides CVE metadata. The vendor advisory for Zimbra Security Advisories offers additional context. Evidence is limited to publicly available information and may not be comprehensive. Defenders should verify mail forwarding restrictions and monitor Sieve notify actions to ensure the security of their Zimbra CollaborationSuite

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.