Description
A CSS sanitization vulnerability in Zimbra Collaboration Suite (ZCS) allows an authenticated user with Briefcase access to publish a document that displays attacker-controlled content under the Zimbra origin. When processing a stylesheet containing non-ASCII characters, DefangFilter appends the final ASCII segment without sanitizing it. HTML stored as application/x-zimbra-doc can therefore retain CSS URL references that the normal sanitizer removes. An attacker can share a crafted document that loads external resources and displays a credential-collection form using Zimbra's own visual assets. Exploitation requires the victim to open the document in a browser that renders the content type inline; credential theft additionally requires form submission. ZCS 10.1.16 and 10.1.20 are affected.
Affected products
synacor: zimbra collaboration suite
References2
- wiki.zimbra.com/wiki/Zimbra_Security_Advisories Vendor Advisory
- www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries… ExploitThird Party Advisory
Metrics
- CVSS 3.1
-
5.4
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N - EPSS — exploit probability
- 0% percentile: 14 · as of 8 November 2026
- CWE
- CWE-79
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