CVE-2026-93630

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 v3 4.3 MEDIUM

4.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact NONE

Integrity Impact LOW

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories
https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/

Configurations

No configuration.

History

23 Oct 2026, 14:17

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-10-23 14:17

Updated : 2026-10-28 20:18

NVD link : CVE-2026-93630

Mitre link : CVE-2026-93630

CVE.ORG link : CVE-2026-93630

JSON object : View

Products Affected

No product.

CWE

CWE-180

Incorrect Behavior Order: Validate Before Canonicalize

{"id": "CVE-2026-93630", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-93630", "role": "CISA Coordinator", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "version": "2.0.3", "timestamp": "2026-10-28T17:48:47.266361Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "cve@rapid7.com", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 4.3, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N", "integrityImpact": "LOW", "userInteraction": "REQUIRED", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "NONE"}, "impactScore": 1.4, "exploitabilityScore": 2.8}]}, "affected": [{"source": "cve@rapid7.com", "affectedData": [{"vendor": "Zimbra", "product": "Zimbra Collaboration Suite", "versions": [{"status": "affected", "version": "0", "lessThan": "10.1.21", "versionType": "semver"}], "defaultStatus": "unaffected"}]}], "published": "2026-10-23T14:17:56.903", "references": [{"url": "https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories", "source": "cve@rapid7.com"}, {"url": "https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/", "source": "cve@rapid7.com"}], "vulnStatus": "Undergoing Analysis", "weaknesses": [{"type": "Secondary", "source": "cve@rapid7.com", "description": [{"lang": "en", "value": "CWE-180"}]}], "descriptions": [{"lang": "en", "value": "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."}], "lastModified": "2026-10-28T20:18:52.513", "sourceIdentifier": "cve@rapid7.com"}