CVE-2026-66912

Stored Cross-Site Scripting in Zimbra

State: Published
Severity: 5.3 Medium
Published: Oct 29, 2026
Updated: Oct 29, 2026
Reserved: Jul 28, 2026

Description

Zimbra is vulnerable to Stored Cross-Site Scripting (XSS) via the From email header during HTML reply composition in Classic UI. Due to insufficient sanitization of the From header value, a remote attacker can send a crafted email containing a malicious From header with an embedded JavaScript payload. When the victim opens the message in Classic UI and clicks Reply while composing in HTML mode with reply headers disabled, the unsanitized From header content is rendered as HTML and the JavaScript payload executes in the victim's browser, potentially allowing the attacker to steal session information or perform actions on behalf of the victim. This issue was fixed in version 10.1.21

Scores

CVSS	Score	Vector	Source
4.0	5.3 Medium	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	CERT-PL

Weaknesses

CWE-79 Improper neutralization of input during web page generation ('cross-site scripting')

Affected Products

Product	Versions
Zimbra CollaborationSynacor	before 10.1.21Affected

References

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

Every record here comes from the CVE Program’s CVE List. © 1999–2026 The MITRE Corporation. CVE is a registered trademark of The MITRE Corporation. The records are reproduced under the CVE Program terms of use.