CVE-2026-93630 Zimbra Collaboration Suite Email HTML Sanitizer Bypass via Hostname Canonicalization
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-93630?
CVE-2026-93630 is a medium-severity vulnerability in Zimbra Collaboration Suite, published on 23 Oct 2026.
Official 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.
Weakness: CWE-180
Which versions are affected by CVE-2026-93630?
How do I fix CVE-2026-93630?
No fix has been published for CVE-2026-93630 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-93630 being exploited?
There is no known exploitation of CVE-2026-93630 in the wild and no public exploit code.
Sources
Also known as GHSA-34q7-82vg-cv73.