{"id":"CVE-2025-66376","kind":"vulnerability","aliases":["CVE-2025-66376"],"related":[],"title":"synacor zimbra collaboration suite: Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading…","description":"Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability in the Classic UI where attackers could abuse Cascading Style Sheets (CSS) @import directives in email HTML.\n\nCISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.","summary":"Zimbra Collaboration Suite's Classic UI has a cross-site scripting flaw: CSS @import directives inside email HTML are abused to run script. An attacker who gets a crafted email in front of a user can run script in that user's Zimbra session, which can expose mail and session data.","severity":"high","cvss":7.2,"epss":null,"exploited":true,"exploited_at":"2026-03-18T00:00:00+00:00","products":[{"name":"Synacor Zimbra Collaboration Suite (ZCS)","fixed":[],"affected":"","ecosystem":"vendor"},{"name":"synacor zimbra collaboration suite","fixed":["10.0.18"],"affected":">= 10.0.0, < 10.0.18","ecosystem":"vendor"},{"name":"synacor zimbra collaboration suite","fixed":["10.1.13"],"affected":">= 10.1.0, < 10.1.13","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["email","exploited","package","self-hosted","zimbra"],"not_affected_if":["managed-hosting","non-classic-ui"],"how_to_check":null,"fix":"Apply the vendor mitigation per Synacor/Zimbra instructions, or discontinue use of the product if mitigations are unavailable (CISA KEV required action). Exact fixed version: unknown.","status":"open","published_at":"2026-01-05T15:15:44+00:00","first_seen_at":"2026-10-23T19:11:51+00:00","triaged_at":"2026-10-23T20:39:05+00:00","updated_at":"2026-10-23T23:44:51+00:00","category":"package","confidence":0.6,"triage":{"at":"2026-10-23T20:39:05Z","model":"claude-haiku-5-5","output":{"fix":"Apply the vendor mitigation per Synacor/Zimbra instructions, or discontinue use of the product if mitigations are unavailable (CISA KEV required action). Exact fixed version: unknown.","reach":"internet","summary":"Zimbra Collaboration Suite's Classic UI has a cross-site scripting flaw: CSS @import directives inside email HTML are abused to run script. An attacker who gets a crafted email in front of a user can run script in that user's Zimbra session, which can expose mail and session data.","category":"package","who_cares":["zimbra","self-hosted","email"],"confidence":0.6,"needs_auth":"no","worst_case":"Attacker runs script in victim's mailbox session and reads or sends mail","analyst_note":"Find the Synacor/Zimbra advisory and the patched or mitigation version, plus whether Classic UI is default; see the CISA KEV entry for CVE-2025-66376.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["managed-hosting","non-classic-ui"],"user_interaction":"yes","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000463,"input_tokens":2601,"output_tokens":405,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-01':141C '-2025':23A,26A '-66376':24A,27A '10':8A '10.0.18':10A '10.1':12A '10.1.13':14A '22':140C 'abus':68B,119C 'action':131C 'allow':15A 'appli':132C 'applic':138C 'attack':73B,117C 'bod':139C 'cascad':21A,120C 'cisa':129C 'classic':16A,52B,114C 'cloud':144C 'collabor':3A,6A,49B,102C 'collaboration':30A,35A,39A 'contain':105C 'could':118C 'craft':77B 'cross':57B,108C 'cross-sit':56B,107C 'css':61B,123C 'cve':22A,25A 'data':99B 'direct':63B,125C 'discontinu':147C 'email':41B,65B,78B,127C 'exploit':42B 'expos':95B 'flaw':60B 'follow':137C 'front':80B 'get':75B 'guidanc':142C 'host':46B 'html':66B,128C 'import':62B,124C 'insid':64B 'instruct':136C 'mail':96B 'mitig':133C,153C 'packag':43B 'per':134C 'product':151C 'requir':130C 'run':70B,85B 'script':59B,71B,86B,110C 'self':45B 'self-host':44B 'servic':145C 'session':92B,98B 'sheet':122C 'site':58B,109C 'store':18A 'style':121C 'suit':4A,50B,103C 'suite':31A,36A,40A 'synacor':1A,28A,33A,37A,100C 'ui':17A,53B,115C 'unavail':155C 'use':148C 'user':83B,89B 'vendor':135C 'via':20A 'vulner':111C 'xss':19A 'zcs':7A,32A,104C 'zimbra':2A,5A,29A,34A,38A,47B,48B,91B,101C","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2026-01-05T15:15:44+00:00","kev":{"dateAdded":"2026-03-18","dueDate":"2026-04-01","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.","knownRansomwareCampaignUse":"Unknown"},"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N","cvss_by":"cve@mitre.org","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2025-66376","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2025-66376","severity":null,"published_at":"2026-03-18T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:51+00:00","fetched_at":"2026-10-25T10:39:04+00:00","note":null},{"source":"nvd","external_id":"CVE-2025-66376","url":"https://nvd.nist.gov/vuln/detail/CVE-2025-66376","severity":null,"published_at":"2026-01-05T15:15:44+00:00","modified_at":"2026-10-07T10:10:00+00:00","first_seen_at":"2026-10-23T23:44:51+00:00","fetched_at":"2026-10-23T23:44:51+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}