icalendar: Denial of service via unbounded VALARM REPEAT expansion

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-77399
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-22 19:16:51 UTC
Updated2026-09-23 18:12:04 UTC
Descriptionicalendar 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.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.003120000 probability, percentile 0.213650000 (date 2026-09-24)

Problem Types: CWE-400 | CWE-834 | CWE-400 CWE-400: Uncontrolled Resource Consumption | CWE-834 CWE-834: Excessive Iteration

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Collective Icalendar affected >= 6.1.0, < 7.2.2 Not specified

References

ReferenceSourceLinkTags
github.com/collective/icalendar/security/advisories/GHSA-qjcq-q7h7-r74v [email protected] github.com
github.com/collective/icalendar/commit/157f85137c65565a308bbcf4fdcc7d8eb... [email protected] github.com
github.com/collective/icalendar/pull/1571 [email protected] github.com
github.com/collective/icalendar/releases/tag/v7.2.2 [email protected] github.com
github.com/collective/icalendar/commit/cddd37226adbc52cca52a399f61d38a37... [email protected] github.com
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