{"id":"CVE-2026-33635","aliases":["DEBIAN-CVE-2026-33635","EUVD-2026-16411","GHSA-pv9c-9mfh-hvxq","UBUNTU-CVE-2026-33635"],"status":"published","title":"iCalendar has ICS injection via unsanitized URI property values","description":"iCalendar is a Ruby library for dealing with iCalendar files in the iCalendar format defined by RFC-5545. Starting in version 2.0.0 and prior to version 2.12.2, .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output. `Icalendar::Values::Uri` falls back to the raw input string when `URI.parse` fails and later serializes it with `value.to_s` without removing or escaping `\\r` or `\\n` characters. That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this). Applications that generate `.ics` files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields. Version 2.12.2 contains a patch for the issue.","severity":{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00254,"percentile":0.17038,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-93"],"published":"2026-03-24T19:13:41Z","modified":"2026-10-28T02:31:14Z","fixes":[{"ecosystem":"RubyGems","package":"icalendar","fixed_in":["2.12.2"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"RubyGems","package":"icalendar","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.0.0"},{"fixed":"2.12.2"}]}]},{"source":"osv","ecosystem":"Debian:12","package":"ruby-icalendar","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.10.0-1","2.10.3-1","2.8.0-1"]},{"source":"osv","ecosystem":"RubyGems","package":"icalendar","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.0.0"},{"fixed":"2.12.2"}]}],"versions":["2.0.0","2.0.1","2.1.0","2.1.1","2.1.2","2.10.0","2.10.1","2.10.2","2.10.3","2.11.0","2.11.1","2.11.2","2.12.0","2.12.1","2.2.0","2.2.1","2.2.2","2.3.0","2.4.0","2.4.1","2.5.0","2.5.1","2.5.2","2.5.3","2.6.0","2.6.1","2.7.0","2.7.1","2.8.0","2.9.0"]},{"source":"osv","ecosystem":"Ubuntu:20.04:LTS","package":"ruby-icalendar","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.4.1-2"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"ruby-icalendar","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.4.1-2","2.7.1-1"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"ruby-icalendar","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.8.0-1","2.10.0-1"]}],"products":[{"vendor":"icalendar","product":"icalendar"},{"vendor":"icalendar_project","product":"icalendar"}],"references":[{"url":"https://github.com/icalendar/icalendar/security/advisories/GHSA-pv9c-9mfh-hvxq","tags":["x_refsource_CONFIRM","Exploit","Mitigation","Vendor Advisory","advisory","web","report"]},{"url":"https://github.com/icalendar/icalendar/commit/b8d23b490363ee5fffaec1d269a8618a912ca265","tags":["x_refsource_MISC","Patch","fix","web","report"]},{"url":"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/icalendar/CVE-2026-33635.yml","tags":["x_refsource_MISC","Mitigation","Vendor Advisory","advisory","web","report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33635","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-pv9c-9mfh-hvxq"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33635.json","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-33635","tags":["advisory"]},{"url":"https://github.com/icalendar/icalendar","tags":["package"]},{"url":"https://ubuntu.com/security/CVE-2026-33635","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-33635","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2026-33635","title":"iCalendar has ICS injection via unsanitized URI property values","description":"iCalendar is a Ruby library for dealing with iCalendar files in the iCalendar format defined by RFC-5545. Starting in version 2.0.0 and prior to version 2.12.2, .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output. `Icalendar::Values::Uri` falls back to the raw input string when `URI.parse` fails and later serializes it with `value.to_s` without removing or escaping `\\r` or `\\n` characters. That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this). Applications that generate `.ics` files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields. Version 2.12.2 contains a patch for the issue.","status":"published","published":"2026-03-26T20:30:43.696Z","modified":"2026-03-30T11:33:48.95Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-93"],"updated_at":"2026-11-02T14:20:07.609948Z"}],"euvd":[{"id":"EUVD-2026-16411","description":"iCalendar is a Ruby library for dealing with iCalendar files in the iCalendar format defined by RFC-5545. Starting in version 2.0.0 and prior to version 2.12.2, .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output. `Icalendar::Values::Uri` falls back to the raw input string when `URI.parse` fails and later serializes it with `value.to_s` without removing or escaping `\\r` or `\\n` characters. That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this). Applications that generate `.ics` files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields. Version 2.12.2 contains a patch for the issue.","status":"published","published":"2026-03-26T20:30:43Z","modified":"2026-03-30T11:33:48Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T19:25:26.376466Z"}],"ghsa":[{"id":"GHSA-pv9c-9mfh-hvxq","title":"iCalendar has ICS injection via unsanitized URI property values","description":"### Summary\n.ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output.\n\n### Details\n`Icalendar::Values::Uri` falls back to the raw input string when `URI.parse` fails and later serializes it with `value.to_s` without removing or escaping `\\r` or `\\n` characters. That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this)\n\nRelevant code:\n- `lib/icalendar/values/uri.rb:16`\n\n### PoC\nRun the following with the library loaded:\n\n```ruby\nrequire \"icalendar/value\"\nrequire \"icalendar/values/uri\"\n\nv = Icalendar::Values::Uri.new(\"https://a.example/ok\\r\\nATTENDEE:mailto:evil@example.com\")\nputs v.to_ical(Icalendar::Values::Text)\n```\n\noutput:\n\n```text\n;VALUE=URI:https://a.example/ok\nATTENDEE:mailto:evil@example.com\n```\n\n### Impact\nApplications that generate `.ics` files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields.\n\n## Fix\nReject raw CR and LF characters in `URI`-typed values before serialization, or escape/encode them so they cannot terminate the current ICS content line.","status":"published","published":"2026-03-24T19:13:41Z","modified":"2026-03-27T22:00:27Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N","level":"medium"}],"cwes":["CWE-93"],"updated_at":"2026-11-02T14:39:44.97342Z"}],"nvd":[{"id":"CVE-2026-33635","description":"iCalendar is a Ruby library for dealing with iCalendar files in the iCalendar format defined by RFC-5545. Starting in version 2.0.0 and prior to version 2.12.2, .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output. `Icalendar::Values::Uri` falls back to the raw input string when `URI.parse` fails and later serializes it with `value.to_s` without removing or escaping `\\r` or `\\n` characters. That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this). Applications that generate `.ics` files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields. Version 2.12.2 contains a patch for the issue.","status":"published","published":"2026-03-26T21:17:07.287Z","modified":"2026-06-17T10:37:49.343Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N","level":"medium","assessor":"secondary"},{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-93"],"updated_at":"2026-11-02T14:12:11.678711Z"}],"osv":[{"id":"CVE-2026-33635","title":"iCalendar has ICS injection via unsanitized URI property values","description":"iCalendar is a Ruby library for dealing with iCalendar files in the iCalendar format defined by RFC-5545. Starting in version 2.0.0 and prior to version 2.12.2, .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output. `Icalendar::Values::Uri` falls back to the raw input string when `URI.parse` fails and later serializes it with `value.to_s` without removing or escaping `\\r` or `\\n` characters. That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this). Applications that generate `.ics` files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields. Version 2.12.2 contains a patch for the issue.","status":"published","published":"2026-03-26T20:30:43.696Z","modified":"2026-10-28T02:31:14.089791112Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N","level":"medium"}],"cwes":["CWE-93"],"updated_at":"2026-11-02T15:45:01.896044Z"},{"id":"DEBIAN-CVE-2026-33635","description":"iCalendar is a Ruby library for dealing with iCalendar files in the iCalendar format defined by RFC-5545. Starting in version 2.0.0 and prior to version 2.12.2, .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output. `Icalendar::Values::Uri` falls back to the raw input string when `URI.parse` fails and later serializes it with `value.to_s` without removing or escaping `\\r` or `\\n` characters. That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this). Applications that generate `.ics` files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields. Version 2.12.2 contains a patch for the issue.","status":"published","published":"2026-03-26T21:17:07.287Z","modified":"2026-10-01T03:03:10.893031329Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T15:45:54.587575Z"},{"id":"GHSA-pv9c-9mfh-hvxq","title":"iCalendar has ICS injection via unsanitized URI property values","description":"### Summary\n.ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output.\n\n### Details\n`Icalendar::Values::Uri` falls back to the raw input string when `URI.parse` fails and later serializes it with `value.to_s` without removing or escaping `\\r` or `\\n` characters. That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this)\n\nRelevant code:\n- `lib/icalendar/values/uri.rb:16`\n\n### PoC\nRun the following with the library loaded:\n\n```ruby\nrequire \"icalendar/value\"\nrequire \"icalendar/values/uri\"\n\nv = Icalendar::Values::Uri.new(\"https://a.example/ok\\r\\nATTENDEE:mailto:evil@example.com\")\nputs v.to_ical(Icalendar::Values::Text)\n```\n\noutput:\n\n```text\n;VALUE=URI:https://a.example/ok\nATTENDEE:mailto:evil@example.com\n```\n\n### Impact\nApplications that generate `.ics` files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields.\n\n## Fix\nReject raw CR and LF characters in `URI`-typed values before serialization, or escape/encode them so they cannot terminate the current ICS content line.","status":"published","published":"2026-03-24T19:13:41Z","modified":"2026-03-27T22:17:39.528683Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N","level":"medium"}],"cwes":["CWE-93"],"updated_at":"2026-11-02T15:46:53.700556Z"},{"id":"UBUNTU-CVE-2026-33635","description":"iCalendar is a Ruby library for dealing with iCalendar files in the iCalendar format defined by RFC-5545. Starting in version 2.0.0 and prior to version 2.12.2, .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output. `Icalendar::Values::Uri` falls back to the raw input string when `URI.parse` fails and later serializes it with `value.to_s` without removing or escaping `\\r` or `\\n` characters. That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this). Applications that generate `.ics` files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields. Version 2.12.2 contains a patch for the issue.","status":"published","published":"2026-03-26T21:17:00Z","modified":"2026-04-14T11:03:23.879612Z","cvss":[{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N","level":"medium"},{"version":"3.1","score":4.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T16:56:16.036833Z"}]}}