CVE-2022-37042: Synacor Zimbra Collaboration Suite (ZCS) Authentication Bypass Vulnerability

CVE-2022-37042 is an authentication bypass vulnerability in Synacor Zimbra Collaboration Suite (ZCS), specifically in the MailboxImportServlet component. It matters because attackers can bypass authentication controls and, when chained with CVE-2022-27925, achieve unauthenticated remote code execution on affected Zimbra servers. This combination has been used in ransomware activity, putting email systems, mailboxes, and connected infrastructure at direct risk.

IT and security teams running Zimbra should treat this as a high-priority exposure: the product is commonly internet-facing for webmail and collaboration, so successful abuse can lead to full server compromise, data theft, and follow-on ransomware. Confirm all version and patch details against the vendor advisory before acting.

How it works

The weakness is classified as CWE-23 (relative path traversal). In this case it manifests as an authentication bypass in MailboxImportServlet. An unauthenticated attacker can abuse the flawed handling of requests to that servlet to gain unauthorized access without valid credentials.

Public reporting indicates the bypass was chained with a separate vulnerability (CVE-2022-27925) to reach unauthenticated remote code execution. Exact request construction and payload details are not repeated here; defenders should obtain mechanics and indicators solely from the vendor advisory and trusted threat-intelligence sources. The practical outcome is that an external attacker who can reach the vulnerable servlet may escalate from no authentication to code execution on the Zimbra host.

Am I affected? How to find it in your systems

Zimbra Collaboration Suite typically runs on Linux servers providing webmail, calendar, and related services, often exposed on HTTPS (ports 443/8443) and sometimes additional admin or proxy ports. Inventory every host that presents Zimbra web interfaces, mailbox services, or the MailboxImportServlet endpoint.

• Query configuration management, asset inventories, and package databases for installed Zimbra Collaboration Suite packages or directories.
• Check running processes, listening services, and web-server virtual hosts that identify as Zimbra.
• Compare installed versions and build numbers against the fixed releases listed in the vendor advisory; do not rely on generic version ranges stated elsewhere.
• Review access logs and reverse-proxy logs for unusual unauthenticated requests targeting MailboxImportServlet or related import/upload paths, especially from unexpected external sources.
• Look for anomalous process creation, new scheduled tasks, or unexpected outbound connections from Zimbra hosts after suspicious servlet activity—these can indicate successful chaining to code execution.

If you cannot confirm the exact patch level, assume the instance is vulnerable until verified against the vendor’s guidance.

How to remediate

Patch first. Apply the updates published by Synacor for Zimbra Collaboration Suite exactly as described in the vendor advisory and follow CISA’s required action: apply updates per vendor instructions. Schedule the maintenance window promptly, take configuration and mailbox backups beforehand, and verify service health after the upgrade.

• After patching, re-check version strings and confirm the MailboxImportServlet no longer exhibits the bypass behavior using any vendor-supplied verification steps.
• Rotate credentials and API keys that may have been accessible from the Zimbra host, and review admin accounts for unauthorized changes.
• Harden the installation: restrict administrative interfaces to management networks, enforce strong authentication, and disable any unused import or servlet features if the vendor documentation permits.
• Ensure the underlying OS and supporting components (web container, Java runtime, libraries) are also current, because residual weaknesses can re-enable similar attack paths.

If you can't patch immediately

Implement compensating controls to reduce exposure until the vendor update can be applied.

• Network segmentation: place Zimbra hosts behind strict firewall rules or a reverse proxy that limits source IPs to known user populations; block direct internet access to administrative and servlet paths where possible.
• Virtual patching / WAF: deploy web-application firewall rules that detect and block anomalous requests to MailboxImportServlet and path-traversal patterns; tune rules against false positives using staging traffic first.
• Feature disablement: if operationally feasible and supported by documentation, disable or restrict the mailbox import functionality until patched.
• Heightened monitoring: increase logging verbosity for the servlet and authentication subsystems, forward logs to a SIEM, and alert on unauthenticated access attempts, unusual file-system activity, or new processes spawned by the Zimbra user.
• Credential and session hygiene: force re-authentication for active sessions and monitor for privilege-escalation indicators.

These measures lower risk but do not replace the vendor patch; schedule the official update as soon as practicable.

If your data may have been exposed

Actively exploited vulnerabilities that enable remote code execution, especially those with known ransomware use, frequently precede data theft and extortion. If your Zimbra environment was reachable and unpatched during the period of exploitation, assume possible mailbox and credential exposure. Preserve logs and disk images for incident response, reset affected credentials, and follow your organization’s breach-notification procedures. You can run a free exposure scan of your email addresses against known breach data sets to check whether associated accounts already appear in public dumps, then prioritize monitoring and password changes accordingly.