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This issue is fixed in version 3.6.3.","state":0,"publishedAt":"2025-12-09T01:16:55.72+00:00","modifiedAt":"2026-10-14T22:10:00.21+00:00","affected":[],"metrics":[{"system":"CVSS 3.1 · security-advisories@github.com · Secondary","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N","score":5.9,"severity":"MEDIUM"}],"references":["https://github.com/traefik/traefik/commit/14a1aedf5704673d875d210d7bacf103a43c77e4","https://github.com/traefik/traefik/releases/tag/v3.6.3","https://github.com/traefik/traefik/security/advisories/GHSA-7vww-mvcr-x6vj"],"sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2025-66491","license":"NIST NVD usage terms; underlying source attribution retained","enrichment":{"sourceStatus":"Analyzed","weaknesses":["CWE-295"],"productCriteria":["cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*"],"sourceDates":{"published":"2025-12-09T01:16:55.720","lastModified":"2026-10-14T22:10:00.210"},"relatedAdvisories":[],"note":"NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON."},"key":"nvd:CVE-2025-66491","identifiers":["CVE-2025-66491"]},"retained":false,"historicalAffected":[]},{"revision":"08fe17db31d7422bba0bcad3fc2a58f1","observedAt":"2026-10-24T13:19:41.952+00:00","statement":{"source":"osv","id":"GHSA-7vww-mvcr-x6vj","aliases":["CVE-2025-66491","GO-2025-4205"],"title":"Traefik Inverted TLS Verification Logic in ingress-nginx Provider","description":"## Impact\n\nThere is a potential vulnerability in Traefik NGINX provider managing the `nginx.ingress.kubernetes.io/proxy-ssl-verify` annotation.\n\nThe provider inverts the semantics of the `nginx.ingress.kubernetes.io/proxy-ssl-verify` annotation. Setting the annotation to `\"on\"` (intending to enable backend TLS certificate verification) actually disables verification, allowing man-in-the-middle attacks against HTTPS backends when operators believe they are protected.\n\n## Patches\n\n- https://github.com/traefik/traefik/releases/tag/v3.6.3\n\n## For more information\n\nIf you have any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues).\n\n<details>\n<summary>Original Description</summary>\n\n### Summary\n\nA logic error in Traefik's experimental ingress-nginx provider inverts the semantics of the `nginx.ingress.kubernetes.io/proxy-ssl-verify` annotation. Setting the annotation to `\"on\"` (intending to enable backend TLS certificate verification) actually disables verification, allowing man-in-the-middle attacks against HTTPS backends when operators believe they are protected.\n\n### Details\n\nIn `pkg/provider/kubernetes/ingress-nginx/kubernetes.go` at line 512, the `InsecureSkipVerify` field is set using inverted logic:\n\n```go\nnst := &namedServersTransport{\n    Name: provider.Normalize(namespace + \"-\" + name),\n    ServersTransport: &dynamic.ServersTransport{\n        ServerName:         ptr.Deref(cfg.ProxySSLName, ptr.Deref(cfg.ProxySSLServerName, \"\")),\n        InsecureSkipVerify: strings.ToLower(ptr.Deref(cfg.ProxySSLVerify, \"off\")) == \"on\",\n    },\n}\n```\n\nThe expression `== \"on\"` evaluates to `true` when the annotation is `\"on\"`, setting `InsecureSkipVerify: true`. In Go's `crypto/tls`, `InsecureSkipVerify: true` means \"do not verify the server's certificate\" — the opposite of what `proxy-ssl-verify: \"on\"` should do according to NGINX semantics.\n\n**Current behavior:**\n| Annotation Value | InsecureSkipVerify | Actual Result |\n|------------------|-------------------|---------------|\n| `\"on\"` | `true` | Verification **disabled** ❌ |\n| `\"off\"` (default) | `false` | Verification **enabled** |\n\n**Expected behavior (per NGINX semantics):**\n| Annotation Value | InsecureSkipVerify | Expected Result |\n|------------------|-------------------|-----------------|\n| `\"on\"` | `false` | Verification **enabled** |\n| `\"off\"` (default) | `true` | Verification **disabled** |\n\nThe test in `pkg/provider/kubernetes/ingress-nginx/kubernetes_test.go` lines 397-403 confirms this inverted behavior is codified as \"expected\":\n\n```go\nServersTransports: map[string]*dynamic.ServersTransport{\n    \"default-ingress-with-proxy-ssl\": {\n        ServerName:         \"whoami.localhost\",\n        InsecureSkipVerify: true,  // Wrong: should be false when annotation is \"on\"\n        RootCAs:            []types.FileOrContent{\"-----BEGIN CERTIFICATE-----\"},\n    },\n},\n```\n\n**Affected versions:** v3.5.0 through current master (introduced in commit `9bd5c617820f2a8d23b50b68d114bb7bc464eccd`)\n\nPavel Kohout\nAisle Research\n</details>\n\n-","state":0,"publishedAt":"2025-12-08T16:43:06+00:00","modifiedAt":"2026-09-10T03:50:31.6895887+00:00","affected":[{"ecosystem":"Go","name":"github.com/traefik/traefik/v3","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"3.5.0"},{"kind":"fixed","version":"3.6.3"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"MODERATE"}],"references":["https://github.com/traefik/traefik/security/advisories/GHSA-7vww-mvcr-x6vj","https://nvd.nist.gov/vuln/detail/CVE-2025-66491","https://github.com/traefik/traefik/commit/14a1aedf5704673d875d210d7bacf103a43c77e4","https://github.com/traefik/traefik","https://github.com/traefik/traefik/releases/tag/v3.6.3"],"sourceUrl":"https://github.com/advisories/GHSA-7vww-mvcr-x6vj","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-7vww-mvcr-x6vj","identifiers":["GHSA-7vww-mvcr-x6vj","CVE-2025-66491","GO-2025-4205"]},"retained":false,"historicalAffected":[]},{"revision":"3eb06018c6f041009d77cb7b09b4c945","observedAt":"2026-10-24T13:19:41.952+00:00","statement":{"source":"osv","id":"GO-2025-4205","aliases":["CVE-2025-66491","GHSA-7vww-mvcr-x6vj"],"title":"Traefik Inverted TLS Verification Logic in ingress-nginx Provider in github.com/traefik/traefik","description":"Traefik Inverted TLS Verification Logic in ingress-nginx Provider in github.com/traefik/traefik","state":0,"publishedAt":"2025-12-15T19:37:35+00:00","modifiedAt":"2026-07-02T14:44:24.3997384+00:00","affected":[{"ecosystem":"Go","name":"github.com/traefik/traefik","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"}]}],"versions":[],"rawVersionEvidence":null},{"ecosystem":"Go","name":"github.com/traefik/traefik/v2","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"}]}],"versions":[],"rawVersionEvidence":null},{"ecosystem":"Go","name":"github.com/traefik/traefik/v3","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"3.5.0"},{"kind":"fixed","version":"3.6.3"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[],"references":["https://github.com/traefik/traefik/security/advisories/GHSA-7vww-mvcr-x6vj","https://nvd.nist.gov/vuln/detail/CVE-2025-66491","https://github.com/traefik/traefik/commit/14a1aedf5704673d875d210d7bacf103a43c77e4","https://github.com/traefik/traefik/releases/tag/v3.6.3"],"sourceUrl":"https://osv.dev/vulnerability/GO-2025-4205","license":"OSV · upstream source license applies","key":"osv:GO-2025-4205","identifiers":["GO-2025-4205","CVE-2025-66491","GHSA-7vww-mvcr-x6vj"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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