collective icalendar up to 7.2.1 Alarm Expansion Logic vInt.from_ical REPEAT resource consumption

Summaryinfo

A vulnerability described as problematic has been identified in collective icalendar up to 7.2.1. This affects the function vInt.from_ical of the component Alarm Expansion Logic. Executing a manipulation of the argument REPEAT can lead to resource consumption. This vulnerability appears as CVE-2026-77399. The attack may be performed from remote. There is no available exploit. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability has been found in collective icalendar up to 7.2.1 and classified as problematic. This vulnerability affects the function vInt.from_ical of the component Alarm Expansion Logic. The manipulation of the argument REPEAT with an unknown input leads to a resource consumption vulnerability. The CWE definition for the vulnerability is CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. As an impact it is known to affect availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability was named CVE-2026-77399 since 08/20/2026. The exploitation appears to be easy. The attack can be initiated remotely. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1499 by the MITRE ATT&CK project.

Upgrading to version 7.2.2 eliminates this vulnerability.

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Productinfo

Type

• Calendar Software

Vendor

• collective

Name

• icalendar

Version

• 7.2.0
• 7.2.1

Website

• Product: https://github.com/collective/icalendar/

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