{"apiVersion":"1.0","identifier":"CVE-2026-55099","description":"icalendar is an RFC 5545 compatible parser and generator of iCalendar files for Python. From 7.1.0 until 7.1.3, the Component equality method in src/icalendar/cal/component.py compares nested subcomponents with two membership loops, and each membership test invokes the same method on child components, causing O(2^n) work relative to nesting depth. Component.from_ical accepts arbitrarily nested BEGIN:VEVENT blocks without a depth limit, so an attacker can submit a sub-kilobyte .ics file containing equal nested subtrees and trigger the cost when an application performs equality, inequality, membership, deduplication, test-assertion, round-trip, or normalization comparisons. Parsing alone does not trigger the issue, and comparisons that differ early short-circuit, but a few hundred bytes can pin a CPU core for minutes or indefinitely, causing denial of service in calendar sync or import endpoints, invite processing, and other comparison paths. This issue is fixed in version 7.1.3.","publishedAt":"2026-08-25T20:16:56","lastModifiedAt":"2026-08-26T16:16:28","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-55099","cvssScore":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","epssProbability":0.00384,"riskScore":0.78,"affectedProduct":"icalendar","affectedVersions":">=7.1.0,<7.1.3","vulnerabilityType":"Library","operatingSystems":[],"links":{"self":"https://www.redsauce.net/api/cves/CVE-2026-55099","webPages":{"es":"https://www.redsauce.net/es/cves/CVE-2026-55099","en":"https://www.redsauce.net/en/cves/CVE-2026-55099","fr":"https://www.redsauce.net/fr/cves/CVE-2026-55099","pt":"https://www.redsauce.net/pt/cves/CVE-2026-55099","de":"https://www.redsauce.net/de/cves/CVE-2026-55099","sk":"https://www.redsauce.net/sk/cves/CVE-2026-55099","el":"https://www.redsauce.net/el/cves/CVE-2026-55099"},"source":"https://nvd.nist.gov/vuln/detail/CVE-2026-55099"}}