CVE-2026-77399mediumCWE-400CWE-834

CVE-2026-77399: medium-severity vulnerability in collective icalendar

icalendar: Denial of service via unbounded VALARM REPEAT expansion

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13Vexday Risk Score

No sign of exploitation. No public exploitation artifact known so far.

ssvc Trackcvss 6.5epss 0.3%
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.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Affected products
collective · icalendar
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