Medium · CVSS 4.3CVE-2026-93630

Zimbra Collaboration Suite Email HTML Sanitizer Bypass via Hostname CanonicalizationCVE-2026-93630

Answer in brief

CVE-2026-93630 records a Medium severity (CVSS 4.3) vulnerability in Zimbra Collaboration Suite Email HTML Sanitizer Bypass via Hostname Canonicalization. The current sources do not mark it as known exploited. The current feed maps Zimbra/Zimbra Collaboration Suite (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 23, 2026Updated Oct 23, 2026Source checked Oct 23, 2026First seen by HOL Oct 23, 2026Material review Oct 23, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 4.3
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 4.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Zimbra/Zimbra Collaboration Suite (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Zimbra/Zimbra Collaboration Suitegeneric	>=0 <10.1.21	10.1.21

Recommended response

Check inventory. Check lockfiles and deployed manifests for Zimbra/Zimbra Collaboration Suite.
Review the reported fix. Update Zimbra/Zimbra Collaboration Suite to 10.1.21 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Oct 23, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 23, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Oct 23, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.