CVE-2026-77399
icalendar: Denial of service via unbounded VALARM REPEAT expansion
- State
- Published
- Severity
- 6.5 Medium
- Published
- Sep 22, 2026
- Updated
- Sep 23, 2026
- Reserved
- Aug 20, 2026
Description
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 6.5 Medium | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H | GitHub_M |
Weaknesses
Affected Products
| Product | Versions |
|---|---|
icalendarcollective |
|
References
- https://github.com/collective/icalendar/security/advisories/GHSA-qjcq-q7h7-r74v
- https://github.com/collective/icalendar/pull/1571
- https://github.com/collective/icalendar/commit/157f85137c65565a308bbcf4fdcc7d8ebce01267
- https://github.com/collective/icalendar/commit/cddd37226adbc52cca52a399f61d38a378221219
- https://github.com/collective/icalendar/releases/tag/v7.2.2
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