---
id: "CVE-2026-93633"
kind: "vulnerability"
aliases: ["CVE-2026-93633"]
title: "Zimbra: CSS sanitizer skips final segment, enabling credential-phishing documents"
severity: "medium"
cvss: 5.4
epss: 0.00235
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["email", "package", "self-hosted", "zimbra"]
not_affected_if: ["managed-hosting", "other-zcs-versions"]
published_at: "2026-10-23T14:17:57+00:00"
first_seen_at: "2026-10-23T21:57:34+00:00"
updated_at: "2026-10-25T12:38:49+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-93633", "first_seen_at": "2026-10-23T21:57:34+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-93633", "first_seen_at": "2026-10-25T12:38:49+00:00"}]
---

# Zimbra: CSS sanitizer skips final segment, enabling credential-phishing documents

Zimbra Collaboration Suite fails to sanitize the last ASCII segment of a stylesheet that contains non-ASCII characters, so a crafted Briefcase document keeps CSS URL references. An attacker can share the document to load external resources and show a fake login form under the Zimbra origin to collect credentials.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed ZCS version with `su - zimbra -c "zmcontrol -v"`, and see whether it is `10.1.16` or `10.1.20`
- unknown for other checks; the sources do not say how to find affected Briefcase documents

## Fix

- Upgrade Zimbra Collaboration Suite past the affected `10.1.16` and `10.1.20` releases; the sources do not name the fixed version
- unknown for configuration workarounds

## Timeline

- 2026-10-23T21:57:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-93633
- 2026-10-25T12:38:49+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-93633

## From the sources

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_