{"id":"GHSA-pv9c-9mfh-hvxq","summary":"iCalendar has ICS injection via unsanitized URI property values","details":"### 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.","aliases":["CVE-2026-33635"],"modified":"2026-03-27T22:17:39.528683Z","published":"2026-03-24T19:13:41Z","database_specific":{"nvd_published_at":"2026-03-26T21:17:07Z","cwe_ids":["CWE-93"],"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2026-03-24T19:13:41Z"},"references":[{"type":"WEB","url":"https://github.com/icalendar/icalendar/security/advisories/GHSA-pv9c-9mfh-hvxq"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33635"},{"type":"WEB","url":"https://github.com/icalendar/icalendar/commit/b8d23b490363ee5fffaec1d269a8618a912ca265"},{"type":"PACKAGE","url":"https://github.com/icalendar/icalendar"},{"type":"WEB","url":"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/icalendar/CVE-2026-33635.yml"}],"affected":[{"package":{"name":"icalendar","ecosystem":"RubyGems","purl":"pkg:gem/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"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/03/GHSA-pv9c-9mfh-hvxq/GHSA-pv9c-9mfh-hvxq.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N"}]}