CVE-2026-66912 Stored Cross-Site Scripting in Zimbra
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-66912?
CVE-2026-66912 is a medium-severity vulnerability in Synacor Zimbra Collaboration, published on 29 Oct 2026.
Official 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
Weakness: CWE-79
Which versions are affected by CVE-2026-66912?
How do I fix CVE-2026-66912?
No fix has been published for CVE-2026-66912 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-66912 being exploited?
There is no known exploitation of CVE-2026-66912 in the wild and no public exploit code.
Sources
Also known as GHSA-rprc-q5mj-4mcw.