CVE-2023-37580

CVE-2023-37580 is a cross-site scripting flaw (CWE-79) in Synacor Zimbra Collaboration Suite's webmail interface, publicly described as a stored XSS in which attacker-supplied content persists and executes in victims' browsers. An attacker delivers crafted content (typically a malicious email or message) that, when viewed by a user in the Zimbra webmail client, runs attacker-controlled JavaScript within that user's authenticated session. Successful execution impacts the confidentiality and integrity of the victim's mailbox: the attacker can steal session cookies or credentials, read or alter mail, and act as the user. Any organization running a vulnerable ZCS release is affected, including self-hosted on-premises deployments and providers hosting Zimbra webmail for customers. CISA added the flaw to its Known Exploited Vulnerabilities catalog on 2023-07-27, confirming exploitation in the wild (ransomware association unknown), while no public proof-of-concept is posted, CVSS is not yet scored, and EPSS assigns a 46.7% probability of exploitation within 30 days (99th percentile).

What to do: Apply the latest ZCS patch release addressing CVE-2023-37580 per the Synacor/Zimbra security advisory, as CISA's required action directs, or discontinue use of the affected deployment if mitigation is unavailable; because the flaw is on the KEV list, prioritize internet-facing webmail servers. While patching is pending, restrict webmail exposure (VPN or IP allowlisting) and review webmail and mail-delivery logs for signs of exploitation. Confirm the installed ZCS version and applied patch level against the vendor advisory, since this dataset does not list fixed version numbers.