CVE-2025-48700 Synacor Zimbra Collaboration Suite (ZCS): web page flaw
In plain words: A web app can be made to act on someone's behalf or reach places it should not. Stolen sessions, actions taken as the victim, or access to internal systems.
Confirmed exploited by CISA on · US federal patch deadline Apr 23, 2026
What to do
- Install Synacor's security update for Zimbra Collaboration Suite (ZCS). If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Keep a list of every internet-facing server you run so nothing is forgotten.
- Patch anything in this catalog first, ahead of normal patch cycles.
- Put admin and file-transfer apps behind a VPN or single sign-on instead of the open internet.
Who is affected
Work IT. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.
What's at risk: Mass data theft and ransomware: a single flaw in a file-transfer or email server has exposed thousands of organisations at once.
The details
- Official name
- Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
- Product
- Synacor Zimbra Collaboration Suite (ZCS)
- CISA description
- Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability that could allow attackers to execute arbitrary JavaScript within the user's session, potentially leading to unauthorized access to sensitive information.
- Type of flaw
- Web page flaw (CWE-79)
- Confirmed exploited
- Apr 20, 2026
- US federal patch deadline
- Apr 23, 2026
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Answering about CVE-2025-48700 ·
Questions about CVE-2025-48700
Is CVE-2025-48700 being exploited?
Yes. CISA added CVE-2025-48700 to its Known Exploited Vulnerabilities catalog on Apr 20, 2026, which means there is reliable evidence of real-world attacks.
How do I fix CVE-2025-48700?
Install Synacor's security update for Zimbra Collaboration Suite (ZCS). If no update exists, follow the vendor's workaround or stop using the product until one ships. Keep a list of every internet-facing server you run so nothing is forgotten.
Am I affected by CVE-2025-48700?
Only if you use Synacor Zimbra Collaboration Suite (ZCS). Aimed mostly at company systems — you are affected through the companies you use, not your own phone.