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CVE-2026-77399— icalendar: Denial of service via unbounded VALARM REPEAT expansion

Quick assessment

Affected
collective icalendar
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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 applica

CVSS 6.5 · Medium

Affected Version Matrix 1

VendorProduct Version RangeStatus
collective icalendar >= 6.1.0, < 7.2.2 affected
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I. Basic Information for CVE-2026-77399

Vulnerability Information

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Vulnerability Title
icalendar: Denial of service via unbounded VALARM REPEAT expansion
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
collective icalendar >= 6.1.0, < 7.2.2 -

II. Public POCs for CVE-2026-77399

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III. Intelligence Information for CVE-2026-77399

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Other References for CVE-2026-77399 (5)

IV. Related Vulnerabilities

Same product: icalendar
Same vendor: collective
Same weakness: CWE-400

V. Comments for CVE-2026-77399

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