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CVE-2026-77399
Published:September 22, 2026
Updated:October 13, 2026
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.
Affected Packages
icalendar (CONDA):
Affected version(s) >=6.1.0 <7.2.2
Fix Suggestion:
Update to version 7.2.2
https://github.com/collective/icalendar.git (GITHUB):
Affected version(s) >=v6.1.0 <v7.2.2
Fix Suggestion:
Update to version v7.2.2
icalendar (PYTHON):
Affected version(s) >=6.1.0 <7.2.2
Fix Suggestion:
Update to version 7.2.2
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CVSS v4
Base Score:
7.1
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
LOW
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
6.5
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Weakness Type (CWE)
Excessive Iteration
Uncontrolled Resource Consumption
EPSS
Base Score:
0.31