{"cve":{"cve_id":"CVE-2026-39821","is_kev":false,"kev_date_added":null,"kev_vendor_project":null,"kev_product":null,"kev_vulnerability_name":null,"kev_short_description":null,"kev_required_action":null,"kev_due_date":null,"kev_known_ransomware":null,"kev_notes":null,"kev_cwes":null,"epss_score":0.00692,"epss_percentile":0.50201,"epss_as_of":"2026-08-26","description":"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\".","published_at":"2026-05-22T15:01:21.462000Z","last_modified_at":"2026-08-27T13:17:48.777000Z","cvss_v3_score":8.2,"cvss_v3_vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N","cvss_v3_severity":"HIGH","cvss_v4_score":null,"cvss_v4_vector":null,"cvss_v4_severity":null,"ssvc_decision":null,"ssvc_exploitation":"none","ssvc_automatable":false,"ssvc_technical_impact":"total","cwes":["CWE-1289"],"nvd_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","https://pkg.go.dev/vuln/GO-2026-5026"],"vuln_status":"Modified","trending_score":null,"is_trending":false,"has_trended":false,"trended_number_one":false,"trending_peak_score":null,"trending_peak_rank":null,"started_trending_at":null,"trended_number_one_at":null,"summary_generated":null,"summary_generated_at":null,"summary_model":null,"created_at":"2026-06-24T00:09:39.878444Z","updated_at":"2026-08-27T17:38:41.369924Z"},"effective_severity":"HIGH","badges":[],"impact_analysis":[],"cvss_v3_decoded":{"version":"3.1","metrics":[{"metric":"AV","name":"Attack Vector","value":"N","value_label":"Network"},{"metric":"AC","name":"Attack Complexity","value":"H","value_label":"High"},{"metric":"PR","name":"Privileges Required","value":"L","value_label":"Low"},{"metric":"UI","name":"User Interaction","value":"N","value_label":"None"},{"metric":"S","name":"Scope","value":"C","value_label":"Changed"},{"metric":"C","name":"Confidentiality","value":"H","value_label":"High"},{"metric":"I","name":"Integrity","value":"H","value_label":"High"},{"metric":"A","name":"Availability","value":"N","value_label":"None"}]},"cvss_v4_decoded":{"version":null,"metrics":[]},"affected":[{"vendor_slug":"golang","vendor_name":"Golang","product_slug":"net","product_name":"net","version_start":null,"version_start_inclusive":null,"version_end":"0.55.0","version_end_inclusive":false,"cpe23_uri":"cpe:2.3:a:golang:net:*:*:*:*:*:go:*:*"},{"vendor_slug":"golang.org-x-net","vendor_name":"golang.org/x/net","product_slug":"golang.org-x-net-idna","product_name":"golang.org/x/net/idna","version_start":"0","version_start_inclusive":true,"version_end":"0.55.0","version_end_inclusive":false,"cpe23_uri":"cve5:golang.org-x-net:golang.org-x-net-idna:0:0.55.0"},{"vendor_slug":"go-standard-library","vendor_name":"Go standard library","product_slug":"net-http","product_name":"net/http","version_start":"1.26.0-0","version_start_inclusive":true,"version_end":"1.26.6","version_end_inclusive":false,"cpe23_uri":"cve5:go-standard-library:net-http:1.26.0-0:1.26.6"},{"vendor_slug":"go-standard-library","vendor_name":"Go standard library","product_slug":"net-http","product_name":"net/http","version_start":"1.27.0-0","version_start_inclusive":true,"version_end":"1.27.0-rc.3","version_end_inclusive":false,"cpe23_uri":"cve5:go-standard-library:net-http:1.27.0-0:1.27.0-rc.3"},{"vendor_slug":"go-standard-library","vendor_name":"Go standard library","product_slug":"net-http","product_name":"net/http","version_start":"0","version_start_inclusive":true,"version_end":"1.25.13","version_end_inclusive":false,"cpe23_uri":"cve5:go-standard-library:net-http:0:1.25.13"},{"vendor_slug":"go-standard-library","vendor_name":"Go standard library","product_slug":"net-http-internal-http2","product_name":"net/http/internal/http2","version_start":"0","version_start_inclusive":true,"version_end":"1.25.13","version_end_inclusive":false,"cpe23_uri":"cve5:go-standard-library:net-http-internal-http2:0:1.25.13"},{"vendor_slug":"go-standard-library","vendor_name":"Go standard library","product_slug":"net-http-internal-http2","product_name":"net/http/internal/http2","version_start":"1.26.0-0","version_start_inclusive":true,"version_end":"1.26.6","version_end_inclusive":false,"cpe23_uri":"cve5:go-standard-library:net-http-internal-http2:1.26.0-0:1.26.6"},{"vendor_slug":"go-standard-library","vendor_name":"Go standard library","product_slug":"net-http-internal-http2","product_name":"net/http/internal/http2","version_start":"1.27.0-0","version_start_inclusive":true,"version_end":"1.27.0-rc.3","version_end_inclusive":false,"cpe23_uri":"cve5:go-standard-library:net-http-internal-http2:1.27.0-0:1.27.0-rc.3"}],"exploit_refs":[],"news":[],"references":[{"url":"https://go.dev/cl/767220","source_type":"MISC","tags":[]},{"url":"https://go.dev/issue/78760","source_type":"MISC","tags":[]},{"url":"https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8","source_type":"MISC","tags":[]},{"url":"https://groups.google.com/g/golang-announce/c/94pEornpRlI","source_type":"MISC","tags":[]},{"url":"https://pkg.go.dev/vuln/GO-2026-5026","source_type":"MISC","tags":[]}],"timeline":[{"type":"published","at":"2026-05-22T15:01:21.462000Z","label":"CVE published","source":null},{"type":"cvss_changed","at":"2026-06-28T17:53:39.415886Z","label":"CVSS score revised","source":"cvelistv5"},{"type":"cvss_changed","at":"2026-06-28T17:53:39.415886Z","label":"CVSS score revised","source":"cvelistv5"},{"type":"cvss_changed","at":"2026-06-28T17:53:39.415886Z","label":"CVSS score revised","source":"cvelistv5"},{"type":"ssvc_changed","at":"2026-06-29T23:46:59.033383Z","label":"SSVC decision revised","source":"vulnrichment"},{"type":"ssvc_changed","at":"2026-06-29T23:46:59.033383Z","label":"SSVC decision revised","source":"vulnrichment"},{"type":"ssvc_changed","at":"2026-06-29T23:46:59.033383Z","label":"SSVC decision revised","source":"vulnrichment"},{"type":"cvss_changed","at":"2026-07-02T13:23:34.995064Z","label":"CVSS score revised","source":"vulnrichment"},{"type":"cvss_changed","at":"2026-07-02T13:23:34.995064Z","label":"CVSS score revised","source":"vulnrichment"},{"type":"cvss_changed","at":"2026-07-02T13:23:34.995064Z","label":"CVSS score revised","source":"vulnrichment"}]}