CVE-2026-33635

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.

• CWE-93

• https://github.com/icalendar/icalendar/commit/b8d23b490363ee5fffaec1d269a8618a912ca265Patch
• https://github.com/icalendar/icalendar/security/advisories/GHSA-pv9c-9mfh-hvxqExploit, Mitigation, Vendor Advisory
• https://github.com/rubysec/ruby-advisory-db/blob/master/gems/icalendar/CVE-2026-33635.ymlMitigation, Vendor Advisory

Published

Mar 26, 2026

Last Modified

Jun 17, 2026

Status

Analyzed