---
id: CVE-2026-93633
title: >-
  Zimbra Collaboration Suite Briefcase CSS Sanitization Bypass via Non-ASCII
  Stylesheet Characters
summary: >-
  A CSS sanitization vulnerability in Zimbra Collaboration Suite (ZCS) allows an
  authenticated user with Briefcase access to publish a document that displays
  attacker-controlled content under the Zimbra origin. When processing a
  stylesheet…
severity: medium
cvss: 5.4
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N'
cvssSource: cna
cwe:
  - CWE-79
vendor: Zimbra
product: Zimbra Collaboration Suite
affected:
  - collaboration_suite <= 10.1.20
published: '2026-10-23'
updated: '2026-10-23'
sourceUpdated: '2026-10-23T13:25:21.365Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-93633'
references:
  - url: 'https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories'
  - url: >-
      https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/
tags:
  - cve.org
ingestedAt: '2026-10-23T14:28:08.711Z'
---

## Overview

A CSS sanitization vulnerability in Zimbra Collaboration Suite (ZCS) allows an authenticated user with Briefcase access to publish a document that displays attacker-controlled content under the Zimbra origin. When processing a stylesheet containing non-ASCII characters, DefangFilter appends the final ASCII segment without sanitizing it. HTML stored as application/x-zimbra-doc can therefore retain CSS URL references that the normal sanitizer removes. An attacker can share a crafted document that loads external resources and displays a credential-collection form using Zimbra's own visual assets. Exploitation requires the victim to open the document in a browser that renders the content type inline; credential theft additionally requires form submission. ZCS 10.1.16 and 10.1.20 are affected.

## Affected

- `collaboration_suite <= 10.1.20`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.