{"cve":"CVE-2026-55099","nvd":{"published":"2026-08-25T20:16:56.940","modified":"2026-09-09T21:07:31.353","status":"Deferred","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-400","CWE-407"],"references":["https://github.com/collective/icalendar/commit/b6b2608ae3af6de40695b4e40f71847485aa0b49","https://github.com/collective/icalendar/commit/cad40cd112c93fd142ec12cc5b37445a849b8a79","https://github.com/collective/icalendar/releases/tag/v7.1.3","https://github.com/collective/icalendar/security/advisories/GHSA-cv84-9p8j-fj68","http://www.openwall.com/lists/oss-security/2026/06/23/8"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:50:17.453294893+00:00"},"epss":{"cve":"CVE-2026-55099","score":0.0063,"percentile":0.50189,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-cv84-9p8j-fj68","url":"https://osv.dev/vulnerability/GHSA-cv84-9p8j-fj68","summary":"icalendar has Algorithmic Complexity in Equality","modified":"2026-09-10T12:25:32.107091999Z","packages":[{"ecosystem":"PyPI","name":"icalendar","purl":"pkg:pypi/icalendar","ranges":[">=7.1.0 <7.1.3"],"fixed":["7.1.3"]}]},{"id":"PYSEC-2026-3851","url":"https://osv.dev/vulnerability/PYSEC-2026-3851","summary":"icalendar has Algorithmic Complexity in Equality","modified":"2026-09-10T12:15:04.992644758Z","packages":[{"ecosystem":"PyPI","name":"icalendar","purl":"pkg:pypi/icalendar","ranges":[">=7.1.0 <7.1.3"],"fixed":["7.1.3"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}