Vulnerability-Lookup

CVE-2026-71325 (GCVE-0-2026-71325)

Vulnerability from cvelistv5 – Published: 2026-08-06 16:24 – Updated: 2026-08-07 17:09

Title

Traefik: `allowCrossNamespace=false` bypass via `@kubernetescrd` TraefikService backendRef

Summary

Traefik is an open-source edge router that makes publishing services a fun and easy experience. Prior to 2.11.54, 3.6.25, and 3.7.10, cross-namespace @kubernetescrd references are not rejected for TraefikService backend references resolved by the service resolver. A tenant confined by RBAC to a single namespace can therefore bind its own router to a TraefikService owned by another namespace and expose or reroute that namespace's backend, defeating the namespace isolation allowCrossNamespace=false is meant to enforce. This issue is fixed in version 2.11.54, 3.6.25, 3.7.10.

Severity

4.8 (Medium)


                        
                          CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-653 - Improper Isolation or Compartmentalization
CWE-863 - Incorrect Authorization

Assigner

GitHub_M

References

5 references

URL	Tags
https://github.com/traefik/traefik/security/advis…	x_refsource_CONFIRM
https://github.com/traefik/traefik/commit/65ebf4b…	x_refsource_MISC
https://github.com/traefik/traefik/releases/tag/v…	x_refsource_MISC
https://github.com/traefik/traefik/releases/tag/v3.6.25	x_refsource_MISC
https://github.com/traefik/traefik/releases/tag/v3.7.10	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
traefik	traefik	Affected: < 2.11.54 Affected: >= 3.0.0, < 3.6.25 Affected: >= 3.7.0, < 3.7.10

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GHSA-62FC-8686-HFMQ

Vulnerability from github – Published: 2026-08-06 16:38 – Updated: 2026-08-06 16:38

Summary

Traefik: `allowCrossNamespace=false` bypass via `@kubernetescrd` TraefikService backendRef

Details

Summary

There is a medium severity vulnerability in Traefik's Kubernetes CRD provider. When providers.kubernetesCRD.allowCrossNamespace is disabled — the default — cross-namespace @kubernetescrd references are rejected for middlewares, TLS options and HTTP/TCP ServersTransports, but the same restriction was not applied to TraefikService backend references resolved by the service resolver. A tenant confined by RBAC to a single namespace can therefore bind its own router to a TraefikService owned by another namespace and expose or reroute that namespace's backend, defeating the namespace isolation allowCrossNamespace=false is meant to enforce. Traefik v2 releases and the unmaintained v3 minor lines below v3.6 are affected and will not receive a patch on their own line; the remedy for those users is upgrading to a maintained, patched release.

Patches

https://github.com/traefik/traefik/releases/tag/v2.11.54
https://github.com/traefik/traefik/releases/tag/v3.6.25
https://github.com/traefik/traefik/releases/tag/v3.7.10

For more information

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

Original Description ### Summary When `providers.kubernetesCRD.allowCrossNamespace=false` (the default), Traefik correctly rejects cross-namespace `@kubernetescrd` references for middlewares, TLS options, and HTTP/TCP `ServersTransport`, but it does not apply the same restriction to service (`TraefikService`) backendRefs. As a result, a Kubernetes tenant who is confined by RBAC to their own namespace can bind their own router to a `TraefikService` owned by another namespace simply by referencing it as `-@kubernetescrd`, defeating the namespace-isolation boundary that `allowCrossNamespace=false` is meant to enforce. This is the service-resolver sibling of the cross-namespace isolation family that Traefik has been fixing one resolver at a time (`df00d82f` / CVE-2026-41174 for Chain middlewares, and `67501cbe` for TCP `ServersTransport`, which shipped in v3.7.7 only four days before the analyzed commit). The `TraefikService` resolver in `configBuilder.nameAndService` was never given the guard its sibling resolvers received. ### Details ### Root cause `nameAndService` only performs the same-namespace check (`isNamespaceAllowed`) inside the branch that handles names without an `@` separator. For names that contain an `@` separator (that is, `@kubernetescrd` cross-namespace references) it applies only the `crossProviderNamespaces` allowlist check, and that check returns `true` by default because a `nil` allowlist means "unrestricted". It never applies the `!allowCrossNamespace && strings.HasSuffix(name, "@kubernetescrd")` rejection that the sibling resolvers all apply, so `allowCrossNamespace=false` is effectively never consulted for `@kubernetescrd` service references. ### Vulnerable code

// pkg/provider/kubernetes/crd/kubernetes_http.go:662-695 — nameAndService (VULNERABLE)
func (c configBuilder) nameAndService(ctx context.Context, parentNamespace string, service traefikv1alpha1.LoadBalancerSpec) (string, *dynamic.Service, error) {
    svcCtx := log.Ctx(ctx).With().Str(logs.ServiceName, service.Name).Logger().WithContext(ctx)

    if !strings.Contains(service.Name, providerNamespaceSeparator) { // 665: only names WITHOUT "@"
        service = *service.DeepCopy()
        service.Namespace = namespaceOrParentNamespace(service.Namespace, parentNamespace)
        if !isNamespaceAllowed(c.allowCrossNamespace, parentNamespace, service.Namespace) { // 669
            return "", nil, fmt.Errorf("service %s/%s not in the parent resource namespace %s", ...)
        }
    }

    // 674: for "@"-names, the ONLY gate is crossProviderNamespaces, which defaults to allow-all (nil).
    if !isCrossProviderNamespaceAllowed(c.crossProviderNamespaces, parentNamespace) && strings.Contains(service.Name, providerNamespaceSeparator) {
        return "", nil, fmt.Errorf("service %q reference is not allowed: ...", service.Name)
    }
    // ^-- MISSING: no `!c.allowCrossNamespace && strings.HasSuffix(service.Name, "@"+ProviderName)` rejection.

    switch service.Kind {
    case "TraefikService":
        return fullServiceName(svcCtx, service, intstr.FromInt(0)), nil, nil // 690: returns the cross-namespace reference
    ...
    }
}

For comparison, the sibling resolver used for middleware and TLS references does carry the guard:

// pkg/provider/kubernetes/crd/kubernetes.go:1653-1668 — resolveReference (CORRECT)
func resolveReference(ctx context.Context, parentNs, ns, name string, crossProviderNamespaces []string, allowCrossNamespace bool) (string, error) {
    if strings.Contains(name, providerNamespaceSeparator) {
        if !allowCrossNamespace && strings.HasSuffix(name, providerNamespaceSeparator+ProviderName) {
            return "", errors.New("when allowCrossNamespace is disabled, @kubernetescrd references are disallowed") // 1656 — THE GUARD
        }
        ...
    }
    ...
}

The same guard is also present at `pkg/provider/kubernetes/crd/kubernetes_http.go:500` (`makeServersTransportKey`, HTTP) and `pkg/provider/kubernetes/crd/kubernetes_tcp.go:316` (`makeTCPServersTransportKey`, TCP, added by commit `67501cbe`). Only the service resolver `nameAndService` lacks it. ### Data flow An `IngressRoute` created by a tenant in namespace `attacker` declares a route service `{ name: "victim-backend@kubernetescrd", kind: TraefikService }`; the tenant controls this reference string. In `nameAndService`, because the name contains `@`, the same-namespace check at line 669 is skipped, and `isCrossProviderNamespaceAllowed(nil, "attacker")` returns `true` under the default `nil` allowlist, so no rejection fires. `fullServiceName` then resolves the reference to the victim namespace's `TraefikService`, and the attacker's HTTP router is generated and bound to the victim's backend. At runtime the attacker's `Host(...)` route forwards to namespace `victim`'s backend pods. ### Default reachability `AllowCrossNamespace` defaults to `false` (`pkg/provider/kubernetes/crd/kubernetes.go:57`, never set to `true` by any `SetDefaults`), so the isolation this bug bypasses is on by default. `CrossProviderNamespaces` defaults to `nil`, and `isCrossProviderNamespaceAllowed` returns `true` for a `nil` allowlist (`pkg/provider/kubernetes/crd/kubernetes.go:1645-1651`), so the only check `nameAndService` applies to an `@`-name is inert by default. The attacker needs only namespace-scoped RBAC to create an `IngressRoute` or `TraefikService` in their own namespace (the standard hard-multi-tenant Traefik setup) and knowledge of the target `TraefikService`'s namespace and name. ### PoC A table-style harness was added to the CRD provider package. It defines a victim `TraefikService` (`backend` in namespace `victim`, backed by a real endpoint) and an attacker `IngressRoute` (namespace `attacker`) that references it via `victim-backend@kubernetescrd`, plus a control route that references a victim `Middleware` via `victim-mw@kubernetescrd`. The control route is given a valid local service so that the only reason it could be dropped is the cross-namespace middleware guard. The provider is run with `AllowCrossNamespace: false` and `CrossProviderNamespaces: nil` (both defaults).

$ go test -run TestPoC_CrossNamespaceServiceBypass ./pkg/provider/kubernetes/crd/ -v

HTTP routers:  [attacker-attacker-svc-route-7df4381938699bd21215]
HTTP services: [victim-whoami-victim-80 victim-backend]
CONTROL OK: cross-ns MIDDLEWARE ref (victim-mw@kubernetescrd) rejected -> router dropped
BYPASS CONFIRMED: attacker router bound to cross-ns service "victim-backend" despite AllowCrossNamespace=false

The control route (middleware reference) is dropped even though it has a valid local service, confirming that the isolation control is active for middlewares; the service route survives and its `Service` field resolves to `victim-backend`, with the victim's services pulled into the generated configuration and reachable through the attacker's router. The harness also runs two corroborating cases. With `AllowCrossNamespace=false` and `CrossProviderNamespaces=["someotherns"]` (an allowlist that excludes the attacker), the service reference is blocked, which proves that the only gate ever applied to an `@kubernetescrd` service name is `crossProviderNamespaces` (inert by default) and that `allowCrossNamespace=false` is never consulted. With `AllowCrossNamespace=true`, both the service and middleware references are accepted, as expected when isolation is intentionally disabled. ### Impact In a multi-tenant cluster relying on `allowCrossNamespace=false` for namespace isolation, a tenant confined to their own namespace can attach their own router (their own `Host` rule and entrypoint) to another tenant's `TraefikService` backend, exposing an otherwise internal-only service on the data plane under the attacker's hostname, and can route or mirror traffic to another namespace's backend that they should not be able to reference.

Severity

4.8 (Medium)


                  
                    CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.11.53"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.11.54"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.6.24"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "3.6.25"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.7.9"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.7.0"
            },
            {
              "fixed": "3.7.10"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "1.7.34"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-71325"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-653",
      "CWE-863"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-06T16:38:37Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "## Summary\n\nThere is a medium severity vulnerability in Traefik\u0027s Kubernetes CRD provider. When `providers.kubernetesCRD.allowCrossNamespace` is disabled \u2014 the default \u2014 cross-namespace `@kubernetescrd` references are rejected for middlewares, TLS options and HTTP/TCP ServersTransports, but the same restriction was not applied to `TraefikService` backend references resolved by the service resolver. A tenant confined by RBAC to a single namespace can therefore bind its own router to a `TraefikService` owned by another namespace and expose or reroute that namespace\u0027s backend, defeating the namespace isolation `allowCrossNamespace=false` is meant to enforce. Traefik v2 releases and the unmaintained v3 minor lines below v3.6 are affected and will not receive a patch on their own line; the remedy for those users is upgrading to a maintained, patched release.\n\n## Patches\n\n- https://github.com/traefik/traefik/releases/tag/v2.11.54\n- https://github.com/traefik/traefik/releases/tag/v3.6.25\n- https://github.com/traefik/traefik/releases/tag/v3.7.10\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\nWhen `providers.kubernetesCRD.allowCrossNamespace=false` (the default), Traefik correctly rejects cross-namespace `@kubernetescrd` references for middlewares, TLS options, and HTTP/TCP `ServersTransport`, but it does not apply the same restriction to service (`TraefikService`) backendRefs. As a result, a Kubernetes tenant who is confined by RBAC to their own namespace can bind their own router to a `TraefikService` owned by another namespace simply by referencing it as `\u003cvictim-namespace\u003e-\u003cname\u003e@kubernetescrd`, defeating the namespace-isolation boundary that `allowCrossNamespace=false` is meant to enforce.\n\nThis is the service-resolver sibling of the cross-namespace isolation family that Traefik has been fixing one resolver at a time (`df00d82f` / CVE-2026-41174 for Chain middlewares, and `67501cbe` for TCP `ServersTransport`, which shipped in v3.7.7 only four days before the analyzed commit). The `TraefikService` resolver in `configBuilder.nameAndService` was never given the guard its sibling resolvers received.\n\n### Details\n### Root cause\n\n`nameAndService` only performs the same-namespace check (`isNamespaceAllowed`) inside the branch that handles names without an `@` separator. For names that contain an `@` separator (that is, `@kubernetescrd` cross-namespace references) it applies only the `crossProviderNamespaces` allowlist check, and that check returns `true` by default because a `nil` allowlist means \"unrestricted\". It never applies the `!allowCrossNamespace \u0026\u0026 strings.HasSuffix(name, \"@kubernetescrd\")` rejection that the sibling resolvers all apply, so `allowCrossNamespace=false` is effectively never consulted for `@kubernetescrd` service references.\n\n### Vulnerable code\n\n```go\n// pkg/provider/kubernetes/crd/kubernetes_http.go:662-695 \u2014 nameAndService (VULNERABLE)\nfunc (c configBuilder) nameAndService(ctx context.Context, parentNamespace string, service traefikv1alpha1.LoadBalancerSpec) (string, *dynamic.Service, error) {\n\tsvcCtx := log.Ctx(ctx).With().Str(logs.ServiceName, service.Name).Logger().WithContext(ctx)\n\n\tif !strings.Contains(service.Name, providerNamespaceSeparator) { // 665: only names WITHOUT \"@\"\n\t\tservice = *service.DeepCopy()\n\t\tservice.Namespace = namespaceOrParentNamespace(service.Namespace, parentNamespace)\n\t\tif !isNamespaceAllowed(c.allowCrossNamespace, parentNamespace, service.Namespace) { // 669\n\t\t\treturn \"\", nil, fmt.Errorf(\"service %s/%s not in the parent resource namespace %s\", ...)\n\t\t}\n\t}\n\n\t// 674: for \"@\"-names, the ONLY gate is crossProviderNamespaces, which defaults to allow-all (nil).\n\tif !isCrossProviderNamespaceAllowed(c.crossProviderNamespaces, parentNamespace) \u0026\u0026 strings.Contains(service.Name, providerNamespaceSeparator) {\n\t\treturn \"\", nil, fmt.Errorf(\"service %q reference is not allowed: ...\", service.Name)\n\t}\n\t// ^-- MISSING: no `!c.allowCrossNamespace \u0026\u0026 strings.HasSuffix(service.Name, \"@\"+ProviderName)` rejection.\n\n\tswitch service.Kind {\n\tcase \"TraefikService\":\n\t\treturn fullServiceName(svcCtx, service, intstr.FromInt(0)), nil, nil // 690: returns the cross-namespace reference\n\t...\n\t}\n}\n```\n\nFor comparison, the sibling resolver used for middleware and TLS references does carry the guard:\n\n```go\n// pkg/provider/kubernetes/crd/kubernetes.go:1653-1668 \u2014 resolveReference (CORRECT)\nfunc resolveReference(ctx context.Context, parentNs, ns, name string, crossProviderNamespaces []string, allowCrossNamespace bool) (string, error) {\n\tif strings.Contains(name, providerNamespaceSeparator) {\n\t\tif !allowCrossNamespace \u0026\u0026 strings.HasSuffix(name, providerNamespaceSeparator+ProviderName) {\n\t\t\treturn \"\", errors.New(\"when allowCrossNamespace is disabled, @kubernetescrd references are disallowed\") // 1656 \u2014 THE GUARD\n\t\t}\n\t\t...\n\t}\n\t...\n}\n```\n\nThe same guard is also present at `pkg/provider/kubernetes/crd/kubernetes_http.go:500` (`makeServersTransportKey`, HTTP) and `pkg/provider/kubernetes/crd/kubernetes_tcp.go:316` (`makeTCPServersTransportKey`, TCP, added by commit `67501cbe`). Only the service resolver `nameAndService` lacks it.\n\n### Data flow\n\nAn `IngressRoute` created by a tenant in namespace `attacker` declares a route service `{ name: \"victim-backend@kubernetescrd\", kind: TraefikService }`; the tenant controls this reference string. In `nameAndService`, because the name contains `@`, the same-namespace check at line 669 is skipped, and `isCrossProviderNamespaceAllowed(nil, \"attacker\")` returns `true` under the default `nil` allowlist, so no rejection fires. `fullServiceName` then resolves the reference to the victim namespace\u0027s `TraefikService`, and the attacker\u0027s HTTP router is generated and bound to the victim\u0027s backend. At runtime the attacker\u0027s `Host(...)` route forwards to namespace `victim`\u0027s backend pods.\n\n### Default reachability\n\n`AllowCrossNamespace` defaults to `false` (`pkg/provider/kubernetes/crd/kubernetes.go:57`, never set to `true` by any `SetDefaults`), so the isolation this bug bypasses is on by default. `CrossProviderNamespaces` defaults to `nil`, and `isCrossProviderNamespaceAllowed` returns `true` for a `nil` allowlist (`pkg/provider/kubernetes/crd/kubernetes.go:1645-1651`), so the only check `nameAndService` applies to an `@`-name is inert by default. The attacker needs only namespace-scoped RBAC to create an `IngressRoute` or `TraefikService` in their own namespace (the standard hard-multi-tenant Traefik setup) and knowledge of the target `TraefikService`\u0027s namespace and name.\n\n### PoC\nA table-style harness was added to the CRD provider package. It defines a victim `TraefikService` (`backend` in namespace `victim`, backed by a real endpoint) and an attacker `IngressRoute` (namespace `attacker`) that references it via `victim-backend@kubernetescrd`, plus a control route that references a victim `Middleware` via `victim-mw@kubernetescrd`. The control route is given a valid local service so that the only reason it could be dropped is the cross-namespace middleware guard. The provider is run with `AllowCrossNamespace: false` and `CrossProviderNamespaces: nil` (both defaults).\n\n```\n$ go test -run TestPoC_CrossNamespaceServiceBypass ./pkg/provider/kubernetes/crd/ -v\n\nHTTP routers:  [attacker-attacker-svc-route-7df4381938699bd21215]\nHTTP services: [victim-whoami-victim-80 victim-backend]\nCONTROL OK: cross-ns MIDDLEWARE ref (victim-mw@kubernetescrd) rejected -\u003e router dropped\nBYPASS CONFIRMED: attacker router bound to cross-ns service \"victim-backend\" despite AllowCrossNamespace=false\n```\n\nThe control route (middleware reference) is dropped even though it has a valid local service, confirming that the isolation control is active for middlewares; the service route survives and its `Service` field resolves to `victim-backend`, with the victim\u0027s services pulled into the generated configuration and reachable through the attacker\u0027s router.\n\nThe harness also runs two corroborating cases. With `AllowCrossNamespace=false` and `CrossProviderNamespaces=[\"someotherns\"]` (an allowlist that excludes the attacker), the service reference is blocked, which proves that the only gate ever applied to an `@kubernetescrd` service name is `crossProviderNamespaces` (inert by default) and that `allowCrossNamespace=false` is never consulted. With `AllowCrossNamespace=true`, both the service and middleware references are accepted, as expected when isolation is intentionally disabled.\n\n### Impact\nIn a multi-tenant cluster relying on `allowCrossNamespace=false` for namespace isolation, a tenant confined to their own namespace can attach their own router (their own `Host` rule and entrypoint) to another tenant\u0027s `TraefikService` backend, exposing an otherwise internal-only service on the data plane under the attacker\u0027s hostname, and can route or mirror traffic to another namespace\u0027s backend that they should not be able to reference.\n\n\n\u003c/details\u003e\n---",
  "id": "GHSA-62fc-8686-hfmq",
  "modified": "2026-08-06T16:38:37Z",
  "published": "2026-08-06T16:38:37Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/security/advisories/GHSA-62fc-8686-hfmq"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/commit/65ebf4b47fbdc33e3856803a5844a404e094d52d"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/traefik/traefik"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v2.11.54"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v3.6.25"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v3.7.10"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Traefik: `allowCrossNamespace=false` bypass via `@kubernetescrd` TraefikService backendRef"
}

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.

Action not permitted

CVE-2026-71325 (GCVE-0-2026-71325)

GHSA-62FC-8686-HFMQ

Summary

Patches

For more information

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