# CVE-2025-48700: Synacor Zimbra Collaboration Suite XSS in Classic UI

Source: https://junglewise.ai/threats/cve-2025-48700-synacor-zimbra-collaboration-suite-xss-in-classic-ui  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-20. Updated: 2026-05-15  
License: CC BY 4.0 with a link back

CVE-2025-48700 · Severity: critical · CVSS 6.1 · Exploited in the wild · Published 2026-04-20

Synacor Zimbra Collaboration Suite, a widely used enterprise email and collaboration platform, contains a security flaw in its 'Classic' web interface. An attacker can send a specially crafted email that, when viewed by a user, executes malicious code in their browser. This could allow the attacker to steal sensitive information, access the user's mailbox, or perform actions on the user's behalf without their knowledge.

Technologies: [Synacor Zimbra Collaboration Suite](https://junglewise.ai/threats/technologies/zimbra-collaboration-suite), [Synacor Zimbra Collaboration Suite (ZCS)](https://junglewise.ai/threats/technologies/zimbra-collaboration-suite-zcs). Vendors: [Synacor](https://junglewise.ai/threats/vendors/synacor).

## Quick answers

**Is CVE-2025-48700 exploited in the wild?** Yes. CVE-2025-48700 is known to be exploited in the wild, first recorded on 20 April 2026. Treat it as urgent.

**How severe is CVE-2025-48700?** Critical severity, with a CVSS score of 6.1, published 20 April 2026.

**Which products and versions are affected?** Synacor Zimbra Collaboration Suite 8.8.15, 9.0, 10.0, 10.1.

**Is there a fix for CVE-2025-48700?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2025-48700 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2025-48700?** Check whether you run Synacor Zimbra Collaboration Suite or Synacor Zimbra Collaboration Suite (ZCS) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A stored Cross-Site Scripting (XSS) vulnerability exists in the Zimbra Classic UI due to insufficient sanitization of HTML content in email messages. The flaw is specifically triggered by crafted tag structures and attribute values containing '@import' directives or other script injection vectors. An unauthenticated remote attacker can exploit this by sending a malicious email to a target user; the payload executes automatically when the victim views the message. This can lead to session hijacking or unauthorized access to sensitive user data. The vulnerability has been observed in active exploitation and affects versions 8.8.15, 9.0, 10.0, and 10.1.

## Affected products

- Synacor Zimbra Collaboration Suite (ZCS) 8.8.15, 9.0, 10.0, 10.1

## Timeline

- 2025-07-11: disclosed: Initial discovery and analysis by NIST
- 2026-04-20: kev added: Added to CISA Known Exploited Vulnerabilities catalog
- 2026-04-20: advisory: Public advisory published

## Related threats

- [Zimbra Collaboration Suite OS command injection in SMTP](https://junglewise.ai/threats/cve-2026-73570-zimbra-collaboration-suite-os-command-injection-in-smtp)
- [Synacor Zimbra Collaboration Suite SSRF in WebEx zimlet](https://junglewise.ai/threats/cve-2020-7796-synacor-zimbra-collaboration-suite-ssrf-in-webex-zimlet)
- [Synacor Zimbra Collaboration Suite stored XSS in Classic UI](https://junglewise.ai/threats/cve-2025-66376-synacor-zimbra-collaboration-suite-stored-xss-in-classic-ui)
- [Synacor Zimbra Collaboration Suite file inclusion in RestFilter servlet](https://junglewise.ai/threats/cve-2025-68645-synacor-zimbra-collaboration-suite-file-inclusion-in-restfilter)
- [Synacor Zimbra Collaboration Suite XSS in Classic Web Client](https://junglewise.ai/threats/cve-2025-27915-synacor-zimbra-collaboration-suite-xss-in-classic-web-client)