Medium, CVSS 4.3RubyGemsPublished
iCalendar has ICS injection via unsanitized URI property values
CVE-2026-33635 · GHSA-pv9c-9mfh-hvxq
- Affected
- RubyGems icalendar >= 2.0.0, < 2.12.2
- Fixed in
- 2.12.2· Vendor fix available
- Issue
- .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output. Details Icalendar::Values::Uri falls back to the raw input string when URI.parse fails and later serializes it with value.tos 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) Relevant code: - lib/icalendar/values/uri.rb:16 PoC Run the following with the library loaded: output: Impact 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…
Recommended action: Upgrade to 2.12.2 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.