{"id":"CVE-2025-66376","published":"2026-01-05T15:15:44Z","modified":"2026-10-07T10:10:00Z","title":"Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability","vendor":"Synacor","product":"Zimbra Collaboration Suite (ZCS)","tier":"core","eol":null,"description":{"text":"Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.","provenance":"source","from":"NVD"},"summary":{"text":"The Zimbra Collaboration Suite (ZCS) Classic UI contains a stored cross-site scripting flaw, caused by improper neutralization of Cascading Style Sheets @import directives in HTML e-mail messages. An attacker who can send an HTML e-mail to a user can exploit it over the network without authentication, but the victim must interact with the message (by opening it in the Classic UI) for the injected script to run.","provenance":"ai","model":"claude-haiku-5-5","generatedAt":"2026-10-31T05:10:46Z"},"cvss":{"score":6.1,"severity":"MEDIUM","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","provenance":"source","from":"NVD"},"epss":{"score":0.20227,"percentile":0.97463,"date":"2026-10-30","provenance":"source"},"kev":{"dateAdded":"2026-03-18","dueDate":"2026-04-01","ransomware":false,"requiredAction":"Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.","notes":"https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories ; https://nvd.nist.gov/vuln/detail/CVE-2025-66376","provenance":"source"},"vulncheckKev":{"dateAdded":"2026-03-17","exploitedFirstSeen":"2026-03-17","ransomware":false,"evidence":[{"url":"https://www.seqrite.com/blog/operation-ghostmail-zimbra-xss-russian-apt-ukraine/","date":"2026-03-17"},{"url":"https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json","date":"2026-03-18"},{"url":"https://unit42.paloaltonetworks.com/russian-webmail-espionage/","date":"2026-07-23"},{"url":"https://www.cisa.gov/news-events/cybersecurity-advisories/aa26-204a","date":"2026-07-23"},{"url":"https://www.proofpoint.com/us/blog/threat-insight/ta488-targets-zimbra-mailservers-half-click-exploits","date":"2026-07-23"},{"url":"https://cydome.io/maritime-cybersecurity-bulletin-july-31st-2026/","date":"2026-07-31"},{"url":"https://www.recordedfuture.com/blog/july-2026-cve-landscape","date":"2026-08-07"},{"url":"https://nukib.gov.cz/cs/infoservis/aktuality/2447-nukib-se-pripojil-k-mezinarodnimu-upozorneni-na-ruskou-kybernetickou-kampan-zneuzivajici-zimbra-collaboration-suite/","date":"2026-08-10"},{"url":"https://www.acn.gov.it/portale/documents/20119/1300791/Operational_Summary_lug26_CLEAR.pdf/88b05799-3e4c-f3ed-4a42-d9e68e080604?t=1787220905144","date":"2026-08-20"}],"evidenceTotal":9,"provenance":"source"},"exploited":true,"otx":{"pulseCount":50,"pulses":[{"name":"Actively_Exploited_Kev | Oct 30, 2026","url":"https://otx.alienvault.com/pulse/6ae35d889ea92b4ce19c2680","created":"2026-10-29"},{"name":"Actively_Exploited_Kev | Oct 29, 2026","url":"https://otx.alienvault.com/pulse/6ae20c1db17e7057ae7d9ad1","created":"2026-10-28"},{"name":"Actively_Exploited_Kev | Oct 28, 2026","url":"https://otx.alienvault.com/pulse/6ae0ba7e0e2a97ff7b218819","created":"2026-10-27"},{"name":"Actively_Exploited_Kev | Oct 27, 2026","url":"https://otx.alienvault.com/pulse/6adf68b85c3e852f3c111d18","created":"2026-10-26"},{"name":"Actively_Exploited_Kev | Oct 24, 2026","url":"https://otx.alienvault.com/pulse/6adb740e397c3ad4799aa4cd","created":"2026-10-23"},{"name":"Actively_Exploited_Kev | Oct 23, 2026","url":"https://otx.alienvault.com/pulse/6ada236fcfba2dfa730ea482","created":"2026-10-22"},{"name":"Actively_Exploited_Kev | Oct 22, 2026","url":"https://otx.alienvault.com/pulse/6ad8d33a077cbb5cab524d80","created":"2026-10-21"},{"name":"Actively_Exploited_Kev | Oct 21, 2026","url":"https://otx.alienvault.com/pulse/6ad78130c4d1ac2be83a8b6d","created":"2026-10-20"},{"name":"Actively_Exploited_Kev | Oct 20, 2026","url":"https://otx.alienvault.com/pulse/6ad62f63c24a405a3423cc13","created":"2026-10-19"},{"name":"Actively_Exploited_Kev | Oct 19, 2026","url":"https://otx.alienvault.com/pulse/6ad4dda174e5797d0bd238b7","created":"2026-10-18"}],"provenance":"machine"},"cwes":[{"id":"CWE-79","name":"Improper Neutralization of Input During Web Page Generation"}],"references":[{"url":"https://wiki.zimbra.com/wiki/Security_Center","tags":["Release Notes","Vendor Advisory"]},{"url":"https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18#Security_Fixes","tags":["Release Notes"]},{"url":"https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13#Security_Fixes","tags":["Release Notes"]},{"url":"https://wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_Policy","tags":["Product"]},{"url":"https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories","tags":["Vendor Advisory"]},{"url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376","tags":["US Government Resource"]}],"techniques":[{"id":"T1566.001","name":"Spearphishing Attachment","tactics":["initial-access"],"provenance":"ai","basis":"ai-mapping","bases":["ai-mapping"],"basisDetail":"claude-haiku-5-5: Malicious HTML email delivers the exploit","mappingType":"exploitation_technique","evidence":[{"from":"description","quote":"allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message","start":69,"end":175}],"model":"claude-haiku-5-5","confidence":"medium","confidenceNote":"AI-mapped from the description (quote-validated, not expert-reviewed)"},{"id":"T1059.007","name":"JavaScript","tactics":["execution"],"provenance":"ai","basis":"ai-mapping","bases":["ai-mapping"],"basisDetail":"claude-haiku-5-5: Stored XSS executes attacker JavaScript in browser","mappingType":"primary_impact","evidence":[{"from":"description","quote":"allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives","start":69,"end":149}],"model":"claude-haiku-5-5","confidence":"medium","confidenceNote":"AI-mapped from the description (quote-validated, not expert-reviewed)"}],"reports":[],"affected":[],"advisories":[],"euvd":{"id":"EUVD-2026-0850","url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-0850","exploited":true,"exploitedSince":"2026-03-18","provenance":"source"},"exploits":[],"exploitSources":null,"exploitRefs":[],"flow":[{"stage":"exploitation","techniques":["T1566.001"],"provenance":"ai"},{"stage":"primary","techniques":["T1059.007"],"provenance":"ai"}],"timeline":[{"date":"2026-01-05","kind":"published","label":"Published (NVD)","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-66376","provenance":"source"},{"date":"2026-03-17","kind":"exploited-reported","label":"Exploitation first reported (VulnCheck KEV evidence)","url":"https://www.seqrite.com/blog/operation-ghostmail-zimbra-xss-russian-apt-ukraine/","provenance":"source"},{"date":"2026-03-18","kind":"kev","label":"Added to CISA KEV","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","provenance":"source"},{"date":"2026-03-18","kind":"euvd-exploited","label":"ENISA EUVD: exploited","url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-0850","provenance":"source"}],"speed":{"daysToPublicExploit":null,"firstExploitFrom":null,"daysToKev":72},"priority":{"score":66.8,"factors":[{"name":"In a KEV catalog","points":35.0,"detail":"listed in CISA KEV and VulnCheck KEV"},{"name":"Recent KEV listing","points":5.0,"detail":"added 228 days ago"},{"name":"Known ransomware use","points":0.0,"detail":"not known"},{"name":"EPSS percentile","points":19.49,"detail":"percentile 0.9746"},{"name":"Named in threat reports","points":0.0,"detail":"0 reports"},{"name":"Public exploit code","points":0.0,"detail":"none found"},{"name":"Mentioned in OTX pulses","points":3.0,"detail":"50 pulses"},{"name":"CVSS severity","points":4.27,"detail":"base score 6.1"},{"name":"End-of-life product","points":0.0,"detail":"supported or unknown"}]},"lineage":{"familyId":"fam-class-synacor-zimbra-collaboration-suite-zcs-cwe-79"}}