CVE-2026-93633
Synacor Zimbra Collaboration Suite: cross-site scripting
- Risk score
- 40/100
- CVSS
- 5.4 v3.1
- Exploit chance (30 days)
- 0.2%
- Published
- 23 Oct 2026
Open in the live forecast Today's forecast
What to know
- What it is
- 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 wit…
- Affected
- Synacor Zimbra Collaboration Suite
- Fix
- Apply the vendor's security update; see the linked advisory.
- Exploitation
- Public proof of concept
Story map
At a glance
Synacor Zimbra Collaboration Suite: Yellow, plan it in. A cross-site request forgery vulnerability in the OAuth extension of Zimbra Collaboration Suite (ZCS) Network Edition allows an attacker to link an attacker-controlled external account to a victim's mailbox. The OAuth callback does not bind its state value or authorization code to the initiating Zimbra session and ins…
The flaws
- CVE-2026-93633: Cross-site scripting (CVSS 5.4 · EPSS 0%)
- CVE-2026-93631: Cross-site request forgery can lead to information disclosure (CVSS 7.1 · EPSS 0%)
- CVE-2026-93638: Cross-site scripting (CVSS 6.1 · EPSS 0%)
The fix
Fix: Apply the vendor's security update; see the linked advisory.
Who is exposed: Synacor Zimbra Collaboration Suite
Where it stands
- Public proof of concept
Connects to
- Same weakness: Cross-site scripting (CWE-79). 399 other warnings in 30 days
- Same product: Earlier Synacor Zimbra Collaboration Suite warnings. 2 in the last 90 days
Why it is Yellow
- CVSS 5.4 medium
- Public exploit or proof of concept referenced
References
Original 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.
Last activity 23 Oct 2026. Patch Forecast updates every hour.