Is CVE-2026-66911 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-66911 being exploited in the wild.

How severe is CVE-2026-66911?

Informational severity, published 29 October 2026.

Which products and versions are affected?

Synacor Zimbra Collaboration before 10.1.21.

Is there a fix for CVE-2026-66911?

Yes: fixed in 10.1.21. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-66911 attacked?

It is attacked over the network, in a web application.

Am I affected by CVE-2026-66911?

Check whether you run Synacor Zimbra Collaboration at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-66911: Zimbra stored XSS via Content-Location MIME header in attachments

CVE-2026-66911 · Severity: info · Published 2026-10-29

Zimbra Collaboration is a messaging and collaboration platform used by organizations for email, calendar, and shared storage. A stored cross-site scripting vulnerability allows an attacker to send a malicious email with a crafted attachment; when a victim opens it in the web interface and clicks the attachment name, attacker-controlled JavaScript executes in the victim's browser, potentially stealing session data or performing actions on their behalf.

Vendors: Synacor.

Quick answers

Is CVE-2026-66911 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-66911 being exploited in the wild.
How severe is CVE-2026-66911?: Informational severity, published 29 October 2026.
Which products and versions are affected?: Synacor Zimbra Collaboration before 10.1.21.
Is there a fix for CVE-2026-66911?: Yes: fixed in 10.1.21. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-66911 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-66911?: Check whether you run Synacor Zimbra Collaboration at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

Fixed in: 10.1.21

Technical details

A stored XSS vulnerability exists in Zimbra's email attachment handling due to insufficient sanitization of the Content-Location MIME header, which an attacker can set to a javascript: URI. An unauthenticated remote attacker sends a crafted email; when the victim opens it in the Zimbra web interface and clicks the attachment link, the JavaScript payload executes with the victim's privileges. The vulnerability was patched in version 10.1.21.

Affected products

Synacor Zimbra Collaboration before 10.1.21

Timeline

2026-10-29: disclosed

References

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