Vulnerability · Published Oct 29, 2026 · Assigned by CERT-PL

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

Medium 5.3

In plain English

A medium-severity cross-site scripting in Zimbra Collaboration from Synacor. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 46% of all known vulnerabilities).

Severity (CVSS 4.0)5.3Medium

Exploit odds (30 days)0.5%top 54.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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

Affected products (as reported)

Vendor	Product	Versions
Synacor	Zimbra Collaboration	0 – before 10.1.21

Weakness: CWE-79 · 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

References

https://cert.pl/en/posts/2026/10/CVE-2026-66911 third-party-advisory
https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories release-notes