GHSA-W2Q5-6Q6X-X959

Vulnerability from github – Published: 2026-05-26 13:30 – Updated: 2026-07-02 12:30
VLAI?
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".

Severity ?
10.0 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Show details on source website
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{
  "affected": [],
  "aliases": [
    "CVE-2026-39821"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1289"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-05-22T16:16:20Z",
    "severity": "CRITICAL"
  },
  "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": "GHSA-w2q5-6q6x-x959",
  "modified": "2026-07-02T12:30:48Z",
  "published": "2026-05-26T13:30:18Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-39821"
    },
    {
      "type": "WEB",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-39821.json"
    },
    {
      "type": "WEB",
      "url": "https://pkg.go.dev/vuln/GO-2026-5026"
    },
    {
      "type": "WEB",
      "url": "https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8"
    },
    {
      "type": "WEB",
      "url": "https://go.dev/issue/78760"
    },
    {
      "type": "WEB",
      "url": "https://go.dev/cl/767220"
    },
    {
      "type": "WEB",
      "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2480756"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/security/cve/CVE-2026-39821"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:34364"
    },
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    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:33524"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:33183"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:33173"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:33163"
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    {
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      "url": "https://access.redhat.com/errata/RHSA-2026:33160"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:33155"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:30855"
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    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:30854"
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    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:30853"
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    {
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      "url": "https://access.redhat.com/errata/RHSA-2026:30650"
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    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:26547"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:26546"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:23264"
    },
    {
      "type": "WEB",
      "url": "https://access.redhat.com/errata/RHSA-2026:23262"
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  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ]
}


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