iCalendar has ICS injection via unsanitized URI property values

Summary

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.

Timeline

1. Mar 26, 2026, 8:30 PM UTCCVE published
2. Mar 30, 2026, 11:33 AM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: partial

3. Mar 30, 2026, 11:33 AM UTCRecord last updated

Affected versions

• icalendar icalendar

  From 2.0.0 · fixed in 2.12.2

• icalendarRubyGems

  From 2.0.0 · fixed in 2.12.2

References 3