{"id":"CVE-2026-55099","state":"PUBLISHED","title":"icalendar: Algorithmic Complexity in Equality","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":"2026-08-25T19:27:02.236Z","updatedAt":"2026-08-26T15:05:26.062Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"GitHub_M"},"assigner":"GitHub_M","products":["collective icalendar"],"affected":[{"vendor":"collective","product":"icalendar","versions":[{"version":">= 7.1.0, < 7.1.3","status":"affected"}]}],"references":["https://github.com/collective/icalendar/security/advisories/GHSA-cv84-9p8j-fj68","https://github.com/collective/icalendar/commit/b6b2608ae3af6de40695b4e40f71847485aa0b49","https://github.com/collective/icalendar/commit/cad40cd112c93fd142ec12cc5b37445a849b8a79","https://github.com/collective/icalendar/releases/tag/v7.1.3","http://www.openwall.com/lists/oss-security/2026/06/23/8"],"weaknesses":["CWE-400","CWE-407"],"ingestedAt":"2026-10-29T20:12:24.861Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/55xxx/CVE-2026-55099.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-55099","state":"PUBLISHED","datePublished":"2026-08-25T19:27:02.236Z","dateUpdated":"2026-08-26T15:05:26.062Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-06-16T14:41:54.579Z"},"containers":{"cna":{"title":"icalendar: Algorithmic Complexity in Equality","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"collective","product":"icalendar","versions":[{"version":">= 7.1.0, < 7.1.3","status":"affected"}]}],"references":[{"url":"https://github.com/collective/icalendar/security/advisories/GHSA-cv84-9p8j-fj68","name":"https://github.com/collective/icalendar/security/advisories/GHSA-cv84-9p8j-fj68","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/collective/icalendar/commit/b6b2608ae3af6de40695b4e40f71847485aa0b49","name":"https://github.com/collective/icalendar/commit/b6b2608ae3af6de40695b4e40f71847485aa0b49","tags":["x_refsource_MISC"]},{"url":"https://github.com/collective/icalendar/commit/cad40cd112c93fd142ec12cc5b37445a849b8a79","name":"https://github.com/collective/icalendar/commit/cad40cd112c93fd142ec12cc5b37445a849b8a79","tags":["x_refsource_MISC"]},{"url":"https://github.com/collective/icalendar/releases/tag/v7.1.3","name":"https://github.com/collective/icalendar/releases/tag/v7.1.3","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":7.5,"baseSeverity":"HIGH","confidentialityImpact":"NONE","integrityImpact":"NONE","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-400","lang":"en","description":"CWE-400: Uncontrolled Resource Consumption","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-407","lang":"en","description":"CWE-407: Inefficient Algorithmic Complexity","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-08-25T19:27:02.236Z"},"source":{"advisory":"GHSA-cv84-9p8j-fj68","discovery":"UNKNOWN"}},"adp":[{"title":"CVE Program Container","references":[{"url":"http://www.openwall.com/lists/oss-security/2026/06/23/8"}],"providerMetadata":{"shortName":"CVE","orgId":"af854a3a-2127-422b-91ae-364da2661108","dateUpdated":"2026-08-25T20:10:56.453Z"}},{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/collective/icalendar/security/advisories/GHSA-cv84-9p8j-fj68","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-26T15:05:19.449076Z","id":"CVE-2026-55099","options":[{"Exploitation":"poc"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-26T15:05:26.062Z"}}]}}}