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.
Published: 2026-10-23
Score: 4.3 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories

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History

Wed, 28 Oct 2026 20:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 23 Oct 2026 23:45:00 +0000

Type Values Removed Values Added
First Time appeared Zimbra
Zimbra zimbra Collaboration Suite
Vendors & Products Zimbra
Zimbra zimbra Collaboration Suite

Fri, 23 Oct 2026 13:30:00 +0000

Type Values Removed Values Added
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.
Title Zimbra Collaboration Suite Email HTML Sanitizer Bypass via Hostname Canonicalization
Weaknesses CWE-180
References
Metrics cvssV3_1

{'score': 4.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N'}


Subscriptions

Zimbra Zimbra Collaboration Suite
cve-icon MITRE

Status: PUBLISHED

Assigner: rapid7

Published:

Updated: 2026-10-28T19:51:28.013Z

Reserved: 2026-09-18T12:22:34.911Z

Link: CVE-2026-93630

cve-icon Vulnrichment

Updated: 2026-10-28T17:48:48.623Z

cve-icon NVD

Status : Undergoing Analysis

Published: 2026-10-23T14:17:56.903

Modified: 2026-10-28T20:18:52.513

Link: CVE-2026-93630

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-23T23:30:17Z

Weaknesses
  • CWE-180

    Incorrect Behavior Order: Validate Before Canonicalize