GHSA-cv84-9p8j-fj68: icalendar (CVE-2026-55099)

Package	Ecosystem	Affected	Fixed in
icalendar	PyPI	>=7.1.0, <7.1.3	7.1.3

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Versions 7.1.0 up to but not including 7.1.3 of the icalendar package are affected. An attacker who can supply iCalendar data to an application that parses it and then compares the parsed components for equality or membership can cause a denial of service. A few hundred bytes of deeply nested components can make one comparison run for minutes or hang the process. Upgrade icalendar to version 7.1.3, which fixes the issue.

Written 1 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
7.5	High	3.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	CNA (GitHub_M)

CISA KEV Not listed.
EPSS 0.0063, the 50th percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:10 UTC First seen by agentprime
31 Oct 2026, 14:10 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.