AIKIDO-2026-800557
icalendar is vulnerable to Uncontrolled Resource Consumption
65
Medium Risk
This Affects:
icalendarTL;DR
The REPEAT property of a VALARM component controls how many additional times an alarm fires, and vInt parses it as a plain integer with no RFC 5545 ceiling. When alarm times are computed through Alarm.triggers or the Alarms helper, both code paths eagerly expand every repetition into an in-memory list with no bound. A crafted calendar with a very large REPEAT value forces huge list allocations that exhaust CPU and memory when untrusted calendar data is processed. The fix caps expansion at icalendar.config.MAX_ALARM_REPEAT and enforces the RFC 5545 signed 32-bit integer range when parsing integers.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and your application computes alarm times from untrusted calendar data.
Background info
icalendar is vulnerable to Uncontrolled Resource Consumption in versions 6.1.0 - 7.2.0.
How to fix this
Upgrade the icalendar library to the patch version.
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SOC 2Compliant
ISO 27001CompliantISO 42001Compliant
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