Resource exhaustion in Collective Icalendar
CVE-2026-77399
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.
Vulnerability class: DoS (Denial of Service)
Published .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
- Collective Icalendar — versions >= 6.1.0, < 7.2.2
Weakness classification (CWE)
References
- github.com/collective/icalendar/commit/157f85137c65565a308bbcf4fdcc7d8ebce01267
- github.com/collective/icalendar/commit/cddd37226adbc52cca52a399f61d38a378221219
- github.com/collective/icalendar/pull/1571
- github.com/collective/icalendar/releases/tag/v7.2.2
- github.com/collective/icalendar/security/advisories/GHSA-qjcq-q7h7-r74v
Frequently asked questions
- What is CVE-2026-77399?
- CVE-2026-77399 is a medium-severity vulnerability in Collective Icalendar, classified under Uncontrolled Resource Consumption. CVSS score: 6.5/10. Published 2026-09-22.
- How severe is CVE-2026-77399?
- Medium severity. CVSS v3 base score is 6.5 out of 10.