Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna

{
  "id": "f10cfeaa6f90d8098a0f937b4b5e5eb25682f5512ce48f8166e3f6858673c196",
  "url": "https://osv.dev/vulnerability/GO-2026-5026",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna",
    "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\".",
    "evidence": "osv:GO-2026-5026",
    "products": [
      {
        "name": {
          "value": "stdlib",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "1.25.13",
            "evidence": "/affected/0/ranges"
          },
          {
            "value": "1.26.6",
            "evidence": "/affected/0/ranges"
          },
          {
            "value": "1.27.0-rc.3",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      },
      {
        "name": {
          "value": "golang.org/x/net",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "0.55.0",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "GO-2026-5026",
      "aliases": [
        "CVE-2026-39821",
        "GO-2026-5026"
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "1.25.13"
                },
                {
                  "introduced": "1.26.0-0"
                },
                {
                  "fixed": "1.26.6"
                },
                {
                  "introduced": "1.27.0-0"
                },
                {
                  "fixed": "1.27.0-rc.3"
                }
              ]
            }
          ],
          "package": {
            "name": "stdlib",
            "purl": "pkg:golang/stdlib",
            "ecosystem": "Go"
          },
          "database_specific": {
            "source": "https://vuln.go.dev/ID/GO-2026-5026.json"
          },
          "ecosystem_specific": {
            "imports": [
              {
                "path": "net/http",
                "symbols": [
                  "Client.CloseIdleConnections",
                  "Client.Do",
                  "Client.Get",
                  "Client.Head",
                  "Client.Post",
                  "Client.PostForm",
                  "ClientConn.Close",
                  "ClientConn.RoundTrip",
                  "Get",
                  "Head",
                  "Post",
                  "PostForm",
                  "Transport.CloseIdleConnections",
                  "Transport.NewClientConn",
                  "Transport.RoundTrip",
                  "http1ClientConn.Close",
                  "http1ClientConn.RoundTrip",
                  "http2ClientConn.RoundTrip",
                  "http2RoundTripper.RoundTrip",
                  "idnaASCII"
                ]
              },
              {
                "path": "net/http/internal/http2",
                "symbols": [
                  "Transport.AddConn",
                  "Transport.RoundTrip",
                  "Transport.RoundTripOpt",
                  "authorityAddr"
                ]
              }
            ]
          }
        },
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "0.55.0"
                }
              ]
            }
          ],
          "package": {
            "name": "golang.org/x/net",
            "purl": "pkg:golang/golang.org/x/net",
            "ecosystem": "Go"
          },
          "database_specific": {
            "source": "https://vuln.go.dev/ID/GO-2026-5026.json"
          },
          "ecosystem_specific": {
            "imports": [
              {
                "path": "golang.org/x/net/idna",
                "symbols": [
                  "Profile.ToASCII",
                  "Profile.ToUnicode",
                  "Profile.process",
                  "ToASCII",
                  "ToUnicode"
                ]
              }
            ]
          }
        }
      ],
      "modified": "2026-10-16T10:42:05.164302476Z",
      "provider": "osv",
      "references": [
        "https://go.dev/cl/767220",
        "https://go.dev/issue/78760",
        "https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8",
        "https://groups.google.com/g/golang-announce/c/94pEornpRlI"
      ],
      "provider_metadata": {
        "url": "https://pkg.go.dev/vuln/GO-2026-5026",
        "review_status": "REVIEWED"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-39821",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 340597,
  "published_at": "2026-05-22T02:46:43+00:00"
}