{"id":"CVE-2026-93628","kind":"vulnerability","aliases":["CVE-2026-93628"],"related":[],"title":"Zimbra Collaboration: forged calendar replies change attendee meeting status","description":"An attendee authentication vulnerability in the email calendar processing of Zimbra Collaboration Suite (ZCS) allows an unauthenticated sender to forge another attendee's response to an existing meeting. Zimbra passes a null sender identity when processing iCalendar REPLY components, causing the attendee authorization filter to be skipped. An attacker who knows the meeting UID, organizer address and attendee address can send a non-outdated reply that changes the attendee's participation status in the organizer's calendar. The change occurs automatically during delivery without organizer or attendee interaction. ZCS 10.1.16 and 10.1.21 are affected.","summary":"Zimbra Collaboration Suite skips its attendee authorization check when processing iCalendar REPLY messages, so an unauthenticated sender can forge another attendee's response to a meeting. An attacker who knows the meeting UID, organizer and attendee addresses can change that attendee's participation status in the organizer's calendar.","severity":"medium","cvss":5.3,"epss":0.00376,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["calendar","email","infrastructure","self-hosted","zimbra"],"not_affected_if":["unknown"],"how_to_check":"- Check the installed Zimbra version with `su - zimbra -c \"zmcontrol -v\"`; the sources name ZCS `10.1.16` and `10.1.21` as affected\n- Unknown whether other versions are affected; the sources do not say","fix":"- Move Zimbra Collaboration Suite off the affected `10.1.16` and `10.1.21` builds to a fixed release; the fixed version is unknown from the sources\n- Unknown whether a configuration workaround exists","status":"open","published_at":"2026-10-23T14:17:56+00:00","first_seen_at":"2026-10-23T21:57:34+00:00","triaged_at":"2026-10-25T04:18:56+00:00","updated_at":"2026-10-25T12:38:49+00:00","category":"infrastructure","confidence":0.6,"triage":{"at":"2026-10-25T04:18:56Z","model":"claude-haiku-5-5","output":{"fix":"- Move Zimbra Collaboration Suite off the affected `10.1.16` and `10.1.21` builds to a fixed release; the fixed version is unknown from the sources\n- Unknown whether a configuration workaround exists","reach":"internet","title":"Zimbra Collaboration: forged calendar replies change attendee meeting status","impact":"low","summary":"Zimbra Collaboration Suite skips its attendee authorization check when processing iCalendar REPLY messages, so an unauthenticated sender can forge another attendee's response to a meeting. An attacker who knows the meeting UID, organizer and attendee addresses can change that attendee's participation status in the organizer's calendar.","category":"infrastructure","nicknames":[],"who_cares":["zimbra","self-hosted","email","calendar"],"confidence":0.6,"needs_auth":"no","worst_case":"Attacker changes an attendee's meeting status in organizer's calendar","analyst_note":"Find the fixed Zimbra version and any workaround at the NVD entry https://nvd.nist.gov/vuln/detail/CVE-2026-93628 or Zimbra's advisory.","how_to_check":"- Check the installed Zimbra version with `su - zimbra -c \"zmcontrol -v\"`; the sources name ZCS `10.1.16` and `10.1.21` as affected\n- Unknown whether other versions are affected; the sources do not say","needs_analyst":true,"not_affected_if":["unknown"],"who_is_affected":"Organizations running Zimbra Collaboration Suite 10.1.16 or 10.1.21 that receive calendar invitations by email are exposed, because the flaw is in automatic delivery of inbound iCalendar replies. Teams on other Zimbra versions, or on hosted Zimbra with the vendor patching for them, can skip it, though the sources do not confirm which versions are unaffected.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"medium"},"cost_usd":0.000689,"input_tokens":3436,"output_tokens":691,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-2026':11A,14A '-93628':12A,15A '10.1.16':162C '10.1.21':164C 'address':59B,127C,130C 'affect':166C 'allow':86C 'anoth':42B,92C 'attack':50B,120C 'attende':7A,28B,43B,58B,63B,73C,93C,113C,129C,141C,159C 'authent':74C 'author':29B,114C 'automat':153C 'calendar':4A,16B,71B,79C,149C 'caus':111C 'chang':6A,61B,139C,151C 'check':30B 'collabor':2A,24B,83C 'compon':110C 'cve':10A,13A 'deliveri':155C 'email':17B,78C 'exist':98C 'filter':115C 'forg':3A,41B,91C 'host':21B 'icalendar':33B,108C 'ident':105C 'infrastructur':18B 'interact':160C 'know':52B,122C 'meet':8A,48B,54B,99C,124C 'messag':35B 'non':135C 'non-outd':134C 'null':103C 'occur':152C 'organ':56B,69B,126C,147C,157C 'outdat':136C 'particip':65B,143C 'pass':101C 'process':32B,80C,107C 'repli':5A,34B,109C,137C 'respons':45B,95C 'self':20B 'self-host':19B 'send':132C 'sender':39B,89C,104C 'skip':26B,118C 'status':9A,66B,144C 'suit':25B,84C 'uid':55B,125C 'unauthent':38B,88C 'vulner':75C 'without':156C 'zcs':85C,161C 'zimbra':1A,22B,23B,82C,100C","nicknames":[],"mitigations":[],"who_affected":"Organizations running Zimbra Collaboration Suite 10.1.16 or 10.1.21 that receive calendar invitations by email are exposed, because the flaw is in automatic delivery of inbound iCalendar replies. Teams on other Zimbra versions, or on hosted Zimbra with the vendor patching for them, can skip it, though the sources do not confirm which versions are unaffected.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-23T14:17:56+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","cvss_by":"cve@rapid7.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-93628","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-93628","severity":null,"published_at":"2026-10-23T14:17:56+00:00","modified_at":"2026-10-23T16:44:17+00:00","first_seen_at":"2026-10-23T21:57:34+00:00","fetched_at":"2026-10-23T22:29:03+00:00","note":null},{"source":"epss","external_id":"CVE-2026-93628","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-93628","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-25T12:38:49+00:00","fetched_at":"2026-10-25T12:38:49+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"}