FKIE_CVE-2026-39821

Vulnerability from fkie_nvd - Published: 2026-05-22 16:16 - Updated: 2026-06-17 10:42
Severity
9.6 (Critical) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
Summary
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".
References
security@golang.orghttps://go.dev/cl/767220Issue Tracking
security@golang.orghttps://go.dev/issue/78760Issue Tracking
security@golang.orghttps://groups.google.com/g/golang-announce/c/iI-mYSI0lu8Mailing List
security@golang.orghttps://pkg.go.dev/vuln/GO-2026-5026Vendor Advisory
Impacted products
Vendor Product Version
golang net *
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "collectionURL": "https://pkg.go.dev",
          "defaultStatus": "unaffected",
          "packageName": "golang.org/x/net/idna",
          "product": "golang.org/x/net/idna",
          "programRoutines": [
            {
              "name": "Profile.process"
            },
            {
              "name": "Profile.ToASCII"
            },
            {
              "name": "Profile.ToUnicode"
            },
            {
              "name": "ToASCII"
            },
            {
              "name": "ToUnicode"
            }
          ],
          "vendor": "golang.org/x/net",
          "versions": [
            {
              "lessThan": "0.55.0",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "source": "security@golang.org"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:golang:net:*:*:*:*:*:go:*:*",
              "matchCriteriaId": "38C86E7B-A1CA-4670-B113-FC9585261F6F",
              "versionEndExcluding": "0.55.0",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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",
  "lastModified": "2026-06-17T10:42:38.333",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 9.6,
          "baseSeverity": "CRITICAL",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "CHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 3.1,
        "impactScore": 5.8,
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-39821",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-05-23T03:55:58.522682Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-05-22T16:16:20.410",
  "references": [
    {
      "source": "security@golang.org",
      "tags": [
        "Issue Tracking"
      ],
      "url": "https://go.dev/cl/767220"
    },
    {
      "source": "security@golang.org",
      "tags": [
        "Issue Tracking"
      ],
      "url": "https://go.dev/issue/78760"
    },
    {
      "source": "security@golang.org",
      "tags": [
        "Mailing List"
      ],
      "url": "https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8"
    },
    {
      "source": "security@golang.org",
      "tags": [
        "Vendor Advisory"
      ],
      "url": "https://pkg.go.dev/vuln/GO-2026-5026"
    }
  ],
  "sourceIdentifier": "security@golang.org",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-1289"
        }
      ],
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "type": "Secondary"
    }
  ]
}


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