---
id: "CVE-2026-66911"
kind: "vulnerability"
aliases: ["CVE-2026-66911"]
title: "Zimbra: crafted email attachment runs JavaScript in webmail"
severity: "medium"
cvss: 5.3
epss: null
exploited: false
status: "open"
category: "other"
products: []
ecosystems: []
tags: ["other", "self-hosted", "webmail", "zimbra"]
not_affected_if: ["version-at-or-above-10.1.21"]
published_at: "2026-10-29T16:18:15+00:00"
first_seen_at: "2026-10-29T16:26:01+00:00"
updated_at: "2026-10-29T16:31:49+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-66911", "first_seen_at": "2026-10-29T16:26:01+00:00"}]
---

# Zimbra: crafted email attachment runs JavaScript in webmail

Zimbra does not sanitize the Content-Location header on email attachments, so a javascript: URI can be stored there. When a victim opens the crafted email and clicks the attachment name, the script runs in their browser inside Zimbra.

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

## How to check

- Check the installed Zimbra version against the fixed version stated in the sources, `10.1.21`.

## Fix

- Zimbra: `10.1.21` or later
- Sources do not state fixes for other release lines.

## Timeline

- 2026-10-29T16:26:01+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-66911

## From the sources

Zimbra is vulnerable to stored cross-site scripting (XSS) via the Content-Location MIME header in email attachments. Due to lack of sanitization of the Content-Location header, an attacker can set it to a javascript: URI. An unauthenticated remote attacker can send a crafted email to a victim; when the victim opens the email in the Zimbra web interface and clicks the attachment name, the JavaScript payload executes in the victim's browser context. This issue was fixed in version 10.1.21

---

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