{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "cpe": "cpe:2.3:a:golang:net:*:*:*:*:*:go:*:*",
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "0.55.0"
              }
            ],
            "source": "CPE_RANGE"
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7770ec48d03fec35e378665337b4faca93c38423"
            }
          ],
          "repo": "https://github.com/golang/net",
          "type": "GIT"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "Go",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/39xxx/CVE-2026-39821.json",
    "unresolved_ranges": [
      {
        "extracted_events": [
          {
            "fixed": "0.55.0"
          }
        ],
        "source": "AFFECTED_FIELD"
      }
    ]
  },
  "details": "The ToASCII and ToUnicode functions incorrectly accept Punycode-encoded labels that decode to an ASCII-only label. For example, ToUnicode(\"xn--example-.com\") incorrectly returns the name \"example.com\" rather than an error. This behavior can lead to privilege escalation in programs using the idna package. For example, a program which performs privilege checks on the ASCII hostname may reject \"example.com\" but permit \"xn--example-.com\". If that program subsequently converts the ASCII hostname to Unicode, it will inadvertently permits access to the Unicode name \"example.com\".",
  "id": "CVE-2026-39821",
  "modified": "2026-08-01T03:32:47.593636847Z",
  "published": "2026-05-22T15:01:21.462Z",
  "references": [
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      "type": "WEB",
      "url": "https://go.dev/cl/767220"
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      "url": "https://go.dev/issue/78760"
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  "schema_version": "1.8.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N",
      "type": "CVSS_V3"
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  "summary": "Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna"
}