Vulnerability-Lookup

GHSA-7VWW-MVCR-X6VJ

Vulnerability from github – Published: 2025-12-08 16:43 – Updated: 2025-12-09 16:32

Summary

Traefik Inverted TLS Verification Logic in ingress-nginx Provider

Details

Impact

There is a potential vulnerability in Traefik NGINX provider managing the nginx.ingress.kubernetes.io/proxy-ssl-verify annotation.

The 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.

Patches

https://github.com/traefik/traefik/releases/tag/v3.6.3

For more information

If you have any questions or comments about this advisory, please open an issue.

Original Description ### Summary A 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. ### Details In `pkg/provider/kubernetes/ingress-nginx/kubernetes.go` at line 512, the `InsecureSkipVerify` field is set using inverted logic:

nst := &namedServersTransport{
    Name: provider.Normalize(namespace + "-" + name),
    ServersTransport: &dynamic.ServersTransport{
        ServerName:         ptr.Deref(cfg.ProxySSLName, ptr.Deref(cfg.ProxySSLServerName, "")),
        InsecureSkipVerify: strings.ToLower(ptr.Deref(cfg.ProxySSLVerify, "off")) == "on",
    },
}

The 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. **Current behavior:** | Annotation Value | InsecureSkipVerify | Actual Result | |------------------|-------------------|---------------| | `"on"` | `true` | Verification **disabled** ❌ | | `"off"` (default) | `false` | Verification **enabled** | **Expected behavior (per NGINX semantics):** | Annotation Value | InsecureSkipVerify | Expected Result | |------------------|-------------------|-----------------| | `"on"` | `false` | Verification **enabled** | | `"off"` (default) | `true` | Verification **disabled** | The test in `pkg/provider/kubernetes/ingress-nginx/kubernetes_test.go` lines 397-403 confirms this inverted behavior is codified as "expected":

ServersTransports: map[string]*dynamic.ServersTransport{
    "default-ingress-with-proxy-ssl": {
        ServerName:         "whoami.localhost",
        InsecureSkipVerify: true,  // Wrong: should be false when annotation is "on"
        RootCAs:            []types.FileOrContent{"-----BEGIN CERTIFICATE-----"},
    },
},

**Affected versions:** v3.5.0 through current master (introduced in commit `9bd5c617820f2a8d23b50b68d114bb7bc464eccd`) Pavel Kohout Aisle Research

Severity

5.9 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.6.2"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.5.0"
            },
            {
              "fixed": "3.6.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-66491"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-295"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-12-08T16:43:06Z",
    "nvd_published_at": "2025-12-09T01:16:55Z",
    "severity": "MODERATE"
  },
  "details": "## 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\u003cdetails\u003e\n\u003csummary\u003eOriginal Description\u003c/summary\u003e\n\n### Summary\n\nA logic error in Traefik\u0027s 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 := \u0026namedServersTransport{\n    Name: provider.Normalize(namespace + \"-\" + name),\n    ServersTransport: \u0026dynamic.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\u0027s `crypto/tls`, `InsecureSkipVerify: true` means \"do not verify the server\u0027s certificate\" \u2014 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** \u274c |\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\u003c/details\u003e\n\n-",
  "id": "GHSA-7vww-mvcr-x6vj",
  "modified": "2025-12-09T16:32:29Z",
  "published": "2025-12-08T16:43:06Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/security/advisories/GHSA-7vww-mvcr-x6vj"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-66491"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/commit/14a1aedf5704673d875d210d7bacf103a43c77e4"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/traefik/traefik"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v3.6.3"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Traefik Inverted TLS Verification Logic in ingress-nginx Provider"
}

CVE-2025-66491 (GCVE-0-2025-66491)

Vulnerability from cvelistv5 – Published: 2025-12-09 00:38 – Updated: 2025-12-09 16:03

Title

Traefik has Inverted TLS Verification Logic in its ingress-nginx Provider

Summary

Traefik is an HTTP reverse proxy and load balancer. Versions 3.5.0 through 3.6.2 have inverted TLS verification logic in 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. This issue is fixed in version 3.6.3.

Severity

5.9 (Medium)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2025-12-09 14:17 UTC

CWE

CWE-295 - Improper Certificate Validation

Assigner

GitHub_M mitre root

References

3 references

URL	Tags
https://github.com/traefik/traefik/security/advis…	x_refsource_CONFIRM
https://github.com/traefik/traefik/commit/14a1aed…	x_refsource_MISC
https://github.com/traefik/traefik/releases/tag/v3.6.3	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
traefik	traefik	Affected: >= 3.5.0, < 3.6.3

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2025-66491",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2025-12-09T14:17:29.439457Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2025-12-09T16:03:28.511Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "traefik",
          "vendor": "traefik",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 3.5.0, \u003c 3.6.3"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Traefik is an HTTP reverse proxy and load balancer. Versions 3.5.0 through 3.6.2 have inverted TLS verification logic in 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. This issue is fixed in version 3.6.3."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 5.9,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-295",
              "description": "CWE-295: Improper Certificate Validation",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-12-09T00:38:39.208Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/traefik/traefik/security/advisories/GHSA-7vww-mvcr-x6vj",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/traefik/traefik/security/advisories/GHSA-7vww-mvcr-x6vj"
        },
        {
          "name": "https://github.com/traefik/traefik/commit/14a1aedf5704673d875d210d7bacf103a43c77e4",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/traefik/traefik/commit/14a1aedf5704673d875d210d7bacf103a43c77e4"
        },
        {
          "name": "https://github.com/traefik/traefik/releases/tag/v3.6.3",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/traefik/traefik/releases/tag/v3.6.3"
        }
      ],
      "source": {
        "advisory": "GHSA-7vww-mvcr-x6vj",
        "discovery": "UNKNOWN"
      },
      "title": "Traefik has Inverted TLS Verification Logic in its ingress-nginx Provider"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2025-66491",
    "datePublished": "2025-12-09T00:38:39.208Z",
    "dateReserved": "2025-12-02T22:44:04.707Z",
    "dateUpdated": "2025-12-09T16:03:28.511Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.