Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS files. When a user…
Severity = CVSS. Probability = EPSS (FIRST). Exploitation = public signals: KEV, EUVD, ransomware, EPSS above 10 %, no account required.
Exploitation probability EPSS · FIRST
Exploitation signals 2 / 5
- KEV catalog (CISA)07 Oct 2025
- Exploited in EUVD (ENISA)07 Oct 2025
- Used by ransomwareno
- EPSS above 10 %4.1%
- No account, over the networkno
What to do
Fix
Apply the vendor’s fix as soon as it is available.
CISA guidance: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Meanwhile
Take the service off the internet or restrict access to it, watch the logs and look for signs of compromise.
Manufacturers (CRA)
Exploited vulnerability in your product: early warning to ENISA within 24 h, then notification within 72 h (Article 14 of the Cyber Resilience Act). The CRA explained
Description ENISA EUVD
An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS files. When a user views an e-mail message containing a malicious ICS entry, its embedded JavaScript executes via an ontoggle event inside a <details> tag. This allows an attacker to run arbitrary JavaScript within the victim's session, potentially leading to unauthorized actions such as setting e-mail filters to redirect messages to an attacker-controlled address. As a result, an attacker can perform unauthorized actions on the victim's account, including e-mail redirection and data exfiltration.
Affected products
Open source packages OSV
Affected libraries according to OSV, with fixed versions.
Timeline
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Published
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Exploitation reported (ENISA)
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Added to the KEV catalog
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CISA remediation due date
References
Other exploited vulnerabilities from the same vendor
- CVE-2026-73570Zimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability8.1 · Actively exploited
- CVE-2025-48700Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability4.3 · Background exploitation
- CVE-2025-66376Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability5.9 · Background exploitation
- CVE-2020-7796Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery Vulnerability9.1 · Background exploitation
- CVE-2025-68645Synacor Zimbra Collaboration Suite (ZCS) PHP Remote File Inclusion Vulnerability7.4 · Background exploitation
- CVE-2019-9621Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery (SSRF) Vulnerability7.8 · Background exploitation