CVE-2026-77399

21th percentile - higher than 21% of all known CVEs

icalendar is an RFC 5545 compatible parser and generator of iCalendar files for Python. From 6.1.0 until 7.2.2, vInt.from_ical accepts an attacker-controlled VALARM REPEAT value and applications that request alarm times can eagerly expand it without an application-level limit. Alarms.times and Alarms.active reach the unbounded expansion in versions starting with 6.1.0, while Alarm.triggers adds a second affected path starting with 7.0.0. Parsing alone does not trigger the issue, but accessing these properties can consume excessive CPU time and heap memory and terminate or stall a service. This issue is fixed in version 7.2.2.

An attacker can supply a malicious iCalendar file that, when alarm properties are accessed, exhausts CPU and memory resources, causing service stall or crash. The risk applies to applications processing untrusted iCalendar files.

Update the icalendar library to version 7.2.2 or later and consider enforcing application-level limits on alarm expansion.