{
  "schema_version": "1.5.0",
  "id": "CURL-CVE-2026-9545",
  "aliases": [
    "CVE-2026-9545"
  ],
  "summary": "exposing HTTP/3 early data",
  "modified": "2026-06-24T09:10:24.00Z",
  "database_specific": {
    "package": "curl",
    "affects": "both",
    "URL": "https://curl.se/docs/CVE-2026-9545.json",
    "www": "https://curl.se/docs/CVE-2026-9545.html",
    "issue": "https://hackerone.com/reports/3752888",
    "CWE": {
      "id": "CWE-200",
      "desc": "Exposure of Sensitive Information to an Unauthorized Actor"
    },
    "last_affected": "8.20.0",
    "severity": "Low"
  },
  "published": "2026-06-24T08:00:00.00Z",
  "affected": [
    {
      "ranges": [
        {
           "type": "SEMVER",
           "events": [
             {"introduced": "8.11.0"},
             {"fixed": "8.21.0"}
           ]
        },
        {
           "type": "GIT",
           "repo": "https://github.com/curl/curl.git",
           "events": [
             {"introduced": "962097b8dd44ed5b9e7984bc1cdffdbdd566857f"},
             {"fixed": "7b9613fa9b1a5e04301a3920eef58e8138dad05e"}
           ]
        }
      ],
      "versions": [
        "8.20.0", "8.19.0", "8.18.0", "8.17.0", "8.16.0", "8.15.0", "8.14.1", 
        "8.14.0", "8.13.0", "8.12.1", "8.12.0", "8.11.1", "8.11.0"
      ]
    }
  ],
  "credits": [
    {
      "name": "Eunsoo Kim (Autonomous Code Security team at Microsoft)",
      "type": "FINDER"
    },
    {
      "name": "Stefan Eissing",
      "type": "REMEDIATION_DEVELOPER"
    }
  ],
  "details": "In this scenario, libcurl first uses a proper HTTP/3 server for the initial\ntransfers, and when it makes a second transfer to the same site it has been\nreplaced by the attacker's impostor machine - without a valid certificate.\n\nWhen libcurl returns to the hostname the second time with a cached SSL session\n(`CURLOPT_SSL_SESSIONID_CACHE` is not disabled) and early data enabled (the\n`CURLSSLOPT_EARLYDATA` bit is set in `CURLOPT_SSL_OPTIONS`), libcurl might\nsend off the second request's bytes on that new connection *before* enforcing\nthe certificate verification failure. Potentially leaking sensitive\ninformation."
}