{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-39821", "assignerOrgId": "1bb62c36-49e3-4200-9d77-64a1400537cc", "state": "PUBLISHED", "assignerShortName": "Go", "dateReserved": "2026-04-07T18:13:03.526Z", "datePublished": "2026-05-22T15:01:21.462Z", "dateUpdated": "2026-05-27T13:13:15.606Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "1bb62c36-49e3-4200-9d77-64a1400537cc", "shortName": "Go", "dateUpdated": "2026-05-22T15:01:21.462Z"}, "title": "Invoking failure to reject ASCII-only Punycode-encoded labels in golang.org/x/net/idna", "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\"."}], "affected": [{"vendor": "golang.org/x/net", "product": "golang.org/x/net/idna", "collectionURL": "https://pkg.go.dev", "packageName": "golang.org/x/net/idna", "versions": [{"version": "0", "lessThan": "0.55.0", "status": "affected", "versionType": "semver"}], "programRoutines": [{"name": "Profile.process"}, {"name": "Profile.ToASCII"}, {"name": "Profile.ToUnicode"}, {"name": "ToASCII"}, {"name": "ToUnicode"}], "defaultStatus": "unaffected"}], "problemTypes": [{"descriptions": [{"lang": "en", "description": "CWE-1289: Improper Validation of Unsafe Equivalence in Input"}]}], "references": [{"url": "https://go.dev/cl/767220"}, {"url": "https://go.dev/issue/78760"}, {"url": "https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8"}, {"url": "https://pkg.go.dev/vuln/GO-2026-5026"}], "credits": [{"lang": "en", "value": "KC1zs4 (https://github.com/KC1zs4)"}]}, "adp": [{"problemTypes": [{"descriptions": [{"type": "CWE", "cweId": "CWE-1289", "lang": "en", "description": "CWE-1289 Improper Validation of Unsafe Equivalence in Input"}]}], "metrics": [{"cvssV3_1": {"scope": "CHANGED", "version": "3.1", "baseScore": 9.6, "attackVector": "NETWORK", "baseSeverity": "CRITICAL", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N", "integrityImpact": "HIGH", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "LOW", "confidentialityImpact": "HIGH"}}, {"other": {"type": "ssvc", "content": {"timestamp": "2026-05-23T03:55:58.522682Z", "id": "CVE-2026-39821", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "total"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-05-27T13:13:15.606Z"}}]}}

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{"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": "2026-05-29T15:26:37.163", "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"}]}, "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"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "[0,0.55.0)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "manual", "scores": [{"score": 100.0, "source": "manual"}]}, "original": {"product": "golang.org/x/net/idna", "source": "cna", "vendor": "golang.org/x/net"}, "product": "net", "vendor": "golang"}], "created": "2026-05-22T16:30:40.167158+00:00", "updated": "2026-05-27T17:00:17.684519+00:00", "vendors": ["golang", "golang$PRODUCT$net"]}