{
  "affected": [
    {
      "database_specific": {
        "source": "https://github.com/ocaml/security-advisories/blob/generated-osv/2026/OSEC-2026-26.json"
      },
      "ecosystem_specific": {
        "affected_bindings": [
          "Runtime_events.read_poll"
        ],
        "opam_constraint": "ocaml {>= \"5\" & < \"5.5.2\"}"
      },
      "package": {
        "ecosystem": "opam",
        "name": "ocaml",
        "purl": "pkg:opam/ocaml"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "5"
            },
            {
              "fixed": "5.5.2"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "ac2fae847a9c2c35ae3bba90a19adbe5d0cc6f59"
            }
          ],
          "repo": "https://github.com/ocaml/ocaml",
          "type": "GIT"
        },
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "de10a6b03a471821cb0b868223e5331b919f48c0"
            }
          ],
          "repo": "https://github.com/ocaml/ocaml",
          "type": "GIT"
        }
      ],
      "versions": [
        "5.0.0",
        "5.0.1",
        "5.1.0",
        "5.1.1",
        "5.1.2",
        "5.2.0",
        "5.2.1",
        "5.2.2",
        "5.3.0",
        "5.3.1",
        "5.4.0",
        "5.4.1",
        "5.4.2",
        "5.5.0",
        "5.5.1",
        "flambda_fork_point",
        "5.5.0-rc1",
        "5.5.0-beta1",
        "5.5.0-alpha3",
        "5.5.0-alpha2",
        "5.5.0-alpha1"
      ]
    }
  ],
  "credits": [
    {
      "name": "Anthropic",
      "type": "REPORTER"
    },
    {
      "name": "Hannes Mehnert",
      "type": "COORDINATOR"
    },
    {
      "name": "Edwin Török",
      "type": "COORDINATOR"
    },
    {
      "name": "Edwin Török",
      "type": "REMEDIATION_REVIEWER"
    },
    {
      "name": "Sadiq Jaffer",
      "type": "REMEDIATION_DEVELOPER"
    }
  ],
  "database_specific": {
    "cwe": [
      "CWE-20",
      "CWE-122"
    ],
    "human_link": "https://github.com/ocaml/security-advisories/tree/main/advisories/2026/OSEC-2026-26.md",
    "osv": "https://github.com/ocaml/security-advisories/tree/generated-osv/2026/OSEC-2026-26.json"
  },
  "details": "ANT-2026-DTBY2HWS \n\nCustom events maintains a cache of user events, it is possible to have a corrupt stream that has a valid message with one message type (which can be custom/unit/span/int) and then has the same event with a different message type.\n\nThis would never be encountered in a real program but can lead to a crash.\n\n## Fix\n\nValidate event type against expected type, report a corrupt stream on mismatch.\n\n## Am I affected?\n\nIf the runtime events producer and consumer run in separate processes, and the producer can be tricked into producing malformed data.\n\n## Timeline\n\n- 2026-08-24: vulnerability was found\n- 2026-08-27: forwarded report to security@ocaml.org\n- 2027-10-20: fix merged to trunk",
  "id": "OSEC-2026-26",
  "modified": "2026-10-28T09:30:03.525644215Z",
  "published": "2026-10-23T21:30:00Z",
  "schema_version": "1.9.2",
  "severity": [
    {
      "score": "CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P",
      "type": "CVSS_V4"
    }
  ],
  "summary": "runtime_events user event name-based type confusion"
}