Vulnerability Description
A hostname canonicalization vulnerability in the email HTML sanitizers of Zimbra Collaboration Suite (ZCS) allows an unauthenticated sender to bypass the restriction on forms that target the Zimbra host. DefangFilter and the OWASP ActionAttributePolicy compare the form-action hostname with the request hostname before browser URL canonicalization. A percent-encoded hostname can therefore survive sanitization while the browser submits the form to the normal Zimbra origin with the recipient's authentication cookie. This permits authenticated form requests from a crafted email after the recipient opens it in Classic and submits the form. The issue is present in ZCS 10.1.16 and 10.1.21. It does not bypass an endpoint's CSRF-token checks; a state-changing attack additionally requires an endpoint that accepts the resulting request without that protection.
CVSS Score
MEDIUM
Related Weaknesses (CWE)
References
- https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories
- https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/
FAQ
What is CVE-2026-93630?
CVE-2026-93630 is a vulnerability with a CVSS score of 4.3 (MEDIUM). A hostname canonicalization vulnerability in the email HTML sanitizers of Zimbra Collaboration Suite (ZCS) allows an unauthenticated sender to bypass the restriction on forms that target the Zimbra ho...
How severe is CVE-2026-93630?
CVE-2026-93630 has been rated MEDIUM with a CVSS base score of 4.3/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-93630?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.