{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "7.1.0"
              },
              {
                "fixed": "7.1.3"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "1300b76fb3fe40d987cc3715735c026b3c1a2191"
            },
            {
              "fixed": "b6b2608ae3af6de40695b4e40f71847485aa0b49"
            },
            {
              "fixed": "cad40cd112c93fd142ec12cc5b37445a849b8a79"
            },
            {
              "fixed": "f7240bc661548f9806c930f2a95ee2f003cfa8ca"
            }
          ],
          "repo": "https://github.com/collective/icalendar",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-cv84-9p8j-fj68"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-400",
      "CWE-407"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55099.json"
  },
  "details": "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.",
  "id": "CVE-2026-55099",
  "modified": "2026-08-28T11:30:57.160713941Z",
  "published": "2026-08-25T19:27:02.236Z",
  "references": [
    {
      "type": "WEB",
      "url": "http://www.openwall.com/lists/oss-security/2026/06/23/8"
    },
    {
      "type": "WEB",
      "url": "https://github.com/collective/icalendar/releases/tag/v7.1.3"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55099.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/collective/icalendar/security/advisories/GHSA-cv84-9p8j-fj68"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-55099"
    },
    {
      "type": "FIX",
      "url": "https://github.com/collective/icalendar/commit/b6b2608ae3af6de40695b4e40f71847485aa0b49"
    },
    {
      "type": "FIX",
      "url": "https://github.com/collective/icalendar/commit/cad40cd112c93fd142ec12cc5b37445a849b8a79"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "icalendar: Algorithmic Complexity in Equality"
}