Vulnerability-Lookup

CVE-2026-40109 (GCVE-0-2026-40109)

Vulnerability from cvelistv5 – Published: 2026-04-09 21:06 – Updated: 2026-04-09 21:06

Title

Flux notification-controller GCR Receiver missing email validation allows unauthorized reconciliation triggering

Summary

Flux notification-controller is the event forwarder and notification dispatcher for the GitOps Toolkit controllers. Prior to 1.8.3, the gcr Receiver type in Flux notification-controller does not validate the email claim of Google OIDC tokens used for Pub/Sub push authentication. This allows any valid Google-issued token, to authenticate against the Receiver webhook endpoint, triggering unauthorized Flux reconciliations. Exploitation requires the attacker to know the Receiver's webhook URL. The webhook path is generated as /hook/sha256sum(token+name+namespace), where the token is a random string stored in a Kubernetes Secret. There is no API or endpoint that enumerates webhook URLs. An attacker cannot discover the path without either having access to the cluster and permissions to read the Receiver's .status.webhookPath in the target namespace, or obtaining the URL through other means (e.g. leaked secrets or access to Pub/Sub config). Upon successful authentication, the controller triggers a reconciliation for all resources listed in the Receiver's .spec.resources. However, the practical impact is limited: Flux reconciliation is idempotent, so if the desired state in the configured sources (Git, OCI, Helm) has not changed, the reconciliation results in a no-op with no effect on cluster state. Additionally, Flux controllers deduplicate reconciliation requests, sending many requests in a short period results in only a single reconciliation being processed. This vulnerability is fixed in 1.8.3.

Severity ?

3.1 (Low)


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

CWE

CWE-287 - Improper Authentication
CWE-345 - Insufficient Verification of Data Authenticity

Assigner

GitHub_M

References

URL

Tags

	https://github.com/fluxcd/notification-controller…	x_refsource_CONFIRM
	https://github.com/fluxcd/notification-controller…	x_refsource_MISC
	https://github.com/fluxcd/notification-controller…	x_refsource_MISC

Impacted products

	Vendor	Product	Version
	fluxcd	notification-controller	Affected: < 1.8.3

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "notification-controller",
          "vendor": "fluxcd",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.8.3"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Flux notification-controller is the event forwarder and notification dispatcher for the GitOps Toolkit controllers. Prior to 1.8.3, the gcr Receiver type in Flux notification-controller does not validate the email claim of Google OIDC tokens used for Pub/Sub push authentication. This allows any valid Google-issued token, to authenticate against the Receiver webhook endpoint, triggering unauthorized Flux reconciliations. Exploitation requires the attacker to know the Receiver\u0027s webhook URL. The webhook path is generated as /hook/sha256sum(token+name+namespace), where the token is a random string stored in a Kubernetes Secret. There is no API or endpoint that enumerates webhook URLs. An attacker cannot discover the path without either having access to the cluster and permissions to read the Receiver\u0027s .status.webhookPath in the target namespace, or obtaining the URL through other means (e.g. leaked secrets or access to Pub/Sub config). Upon successful authentication, the controller triggers a reconciliation for all resources listed in the Receiver\u0027s .spec.resources. However, the practical impact is limited: Flux reconciliation is idempotent, so if the desired state in the configured sources (Git, OCI, Helm) has not changed, the reconciliation results in a no-op with no effect on cluster state. Additionally, Flux controllers deduplicate reconciliation requests, sending many requests in a short period results in only a single reconciliation being processed. This vulnerability is fixed in 1.8.3."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 3.1,
            "baseSeverity": "LOW",
            "confidentialityImpact": "NONE",
            "integrityImpact": "LOW",
            "privilegesRequired": "LOW",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-287",
              "description": "CWE-287: Improper Authentication",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-345",
              "description": "CWE-345: Insufficient Verification of Data Authenticity",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-04-09T21:06:59.688Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/fluxcd/notification-controller/security/advisories/GHSA-h9cx-xjg6-5v2w",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/fluxcd/notification-controller/security/advisories/GHSA-h9cx-xjg6-5v2w"
        },
        {
          "name": "https://github.com/fluxcd/notification-controller/pull/1279",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/fluxcd/notification-controller/pull/1279"
        },
        {
          "name": "https://github.com/fluxcd/notification-controller/releases/tag/v1.8.3",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/fluxcd/notification-controller/releases/tag/v1.8.3"
        }
      ],
      "source": {
        "advisory": "GHSA-h9cx-xjg6-5v2w",
        "discovery": "UNKNOWN"
      },
      "title": "Flux notification-controller GCR Receiver missing email validation allows unauthorized reconciliation triggering"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-40109",
    "datePublished": "2026-04-09T21:06:59.688Z",
    "dateReserved": "2026-04-09T01:41:38.536Z",
    "dateUpdated": "2026-04-09T21:06:59.688Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-40109\",\"sourceIdentifier\":\"security-advisories@github.com\",\"published\":\"2026-04-09T21:16:12.277\",\"lastModified\":\"2026-04-09T21:16:12.277\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"Flux notification-controller is the event forwarder and notification dispatcher for the GitOps Toolkit controllers. Prior to 1.8.3, the gcr Receiver type in Flux notification-controller does not validate the email claim of Google OIDC tokens used for Pub/Sub push authentication. This allows any valid Google-issued token, to authenticate against the Receiver webhook endpoint, triggering unauthorized Flux reconciliations. Exploitation requires the attacker to know the Receiver\u0027s webhook URL. The webhook path is generated as /hook/sha256sum(token+name+namespace), where the token is a random string stored in a Kubernetes Secret. There is no API or endpoint that enumerates webhook URLs. An attacker cannot discover the path without either having access to the cluster and permissions to read the Receiver\u0027s .status.webhookPath in the target namespace, or obtaining the URL through other means (e.g. leaked secrets or access to Pub/Sub config). Upon successful authentication, the controller triggers a reconciliation for all resources listed in the Receiver\u0027s .spec.resources. However, the practical impact is limited: Flux reconciliation is idempotent, so if the desired state in the configured sources (Git, OCI, Helm) has not changed, the reconciliation results in a no-op with no effect on cluster state. Additionally, Flux controllers deduplicate reconciliation requests, sending many requests in a short period results in only a single reconciliation being processed. This vulnerability is fixed in 1.8.3.\"}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N\",\"baseScore\":3.1,\"baseSeverity\":\"LOW\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"HIGH\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"LOW\",\"availabilityImpact\":\"NONE\"},\"exploitabilityScore\":1.6,\"impactScore\":1.4}]},\"weaknesses\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-287\"},{\"lang\":\"en\",\"value\":\"CWE-345\"}]}],\"references\":[{\"url\":\"https://github.com/fluxcd/notification-controller/pull/1279\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/fluxcd/notification-controller/releases/tag/v1.8.3\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/fluxcd/notification-controller/security/advisories/GHSA-h9cx-xjg6-5v2w\",\"source\":\"security-advisories@github.com\"}]}}"
  }
}

GHSA-H9CX-XJG6-5V2W

Vulnerability from github – Published: 2026-04-10 20:18 – Updated: 2026-04-10 20:18

Summary

Flux notification-controller GCR Receiver missing email validation allows unauthorized reconciliation triggering

Details

Impact

The gcr Receiver type in Flux notification-controller does not validate the email claim of Google OIDC tokens used for Pub/Sub push authentication. This allows any valid Google-issued token, to authenticate against the Receiver webhook endpoint, triggering unauthorized Flux reconciliations.

Exploitation requires the attacker to know the Receiver's webhook URL. The webhook path is generated as /hook/sha256sum(token+name+namespace), where the token is a random string stored in a Kubernetes Secret. There is no API or endpoint that enumerates webhook URLs. An attacker cannot discover the path without either having access to the cluster and permissions to read the Receiver's .status.webhookPath in the target namespace, or obtaining the URL through other means (e.g. leaked secrets or access to Pub/Sub config).

Upon successful authentication, the controller triggers a reconciliation for all resources listed in the Receiver's .spec.resources. However, the practical impact is limited: Flux reconciliation is idempotent, so if the desired state in the configured sources (Git, OCI, Helm) has not changed, the reconciliation results in a no-op with no effect on cluster state. Additionally, Flux controllers deduplicate reconciliation requests, sending many requests in a short period results in only a single reconciliation being processed.

Patches

The fix in notification-controller v1.8.3 refactors the GCR Receiver authentication to allow users to extend the verification to email and audience claims in the JWT. This enables operators to configure their Receiver's secret with the expected GCP Service Account email and audience, which the controller will validate against the token's claims before accepting the request.

Email validation example:

apiVersion: v1
kind: Secret
metadata:
  name: gcr-webhook-token
  namespace: apps
type: Opaque
stringData:
  token: <random token>
  email: <service-account>@<project>.iam.gserviceaccount.com
  audience: https://<hostname>/hook/<sha256(token+name+namespace)>

For more information, please see the GCR Receiver documentation: https://fluxcd.io/flux/components/notification/receivers/#gcr

Credits

Thanks to Saroj Khadka for reporting this issue to the Flux Security Team.

Severity ?

3.1 (Low)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/fluxcd/notification-controller"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.8.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-40109"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-287",
      "CWE-345"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-10T20:18:16Z",
    "nvd_published_at": "2026-04-09T21:16:12Z",
    "severity": "LOW"
  },
  "details": "### Impact\n\nThe `gcr` Receiver type in Flux notification-controller does not validate the `email` claim of Google OIDC tokens used for Pub/Sub push authentication. This allows any valid Google-issued token, to authenticate against the Receiver webhook endpoint, triggering unauthorized Flux reconciliations.\n\nExploitation requires the attacker to know the Receiver\u0027s webhook URL. The webhook path is generated as `/hook/sha256sum(token+name+namespace)`, where the token is a random string stored in a Kubernetes Secret. There is no API or endpoint that enumerates webhook URLs. An attacker cannot discover the path without either having access to the cluster and permissions to read the Receiver\u0027s `.status.webhookPath` in the target namespace, or obtaining the URL through other means (e.g. leaked secrets or access to Pub/Sub config).\n\nUpon successful authentication, the controller triggers a reconciliation for all resources listed in the Receiver\u0027s `.spec.resources`. However, the practical impact is limited: Flux reconciliation is idempotent, so if the desired state in the configured sources (Git, OCI, Helm) has not changed, the reconciliation results in a no-op with no effect on cluster state. Additionally, Flux controllers deduplicate reconciliation requests, sending many requests in a short period results in only a single reconciliation being processed.\n\n### Patches\n\nThe fix in notification-controller v1.8.3 refactors the GCR Receiver authentication to allow users to extend the verification to `email` and `audience` claims in the JWT. This enables operators to configure their Receiver\u0027s secret with the expected GCP Service Account email and audience, which the controller will validate against the token\u0027s claims before accepting the request.\n\nEmail validation example:\n\n```yaml\napiVersion: v1\nkind: Secret\nmetadata:\n  name: gcr-webhook-token\n  namespace: apps\ntype: Opaque\nstringData:\n  token: \u003crandom token\u003e\n  email: \u003cservice-account\u003e@\u003cproject\u003e.iam.gserviceaccount.com\n  audience: https://\u003chostname\u003e/hook/\u003csha256(token+name+namespace)\u003e\n```\n\nFor more information, please see the GCR Receiver documentation: https://fluxcd.io/flux/components/notification/receivers/#gcr\n\n\n### Credits\n\nThanks to Saroj Khadka for reporting this issue to the Flux Security Team.",
  "id": "GHSA-h9cx-xjg6-5v2w",
  "modified": "2026-04-10T20:18:16Z",
  "published": "2026-04-10T20:18:16Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/fluxcd/notification-controller/security/advisories/GHSA-h9cx-xjg6-5v2w"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-40109"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fluxcd/notification-controller/pull/1279"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/fluxcd/notification-controller"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fluxcd/notification-controller/releases/tag/v1.8.3"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Flux notification-controller GCR Receiver missing email validation allows unauthorized reconciliation triggering"
}

FKIE_CVE-2026-40109

Vulnerability from fkie_nvd - Published: 2026-04-09 21:16 - Updated: 2026-04-09 21:16

Severity ?

3.1 (Low) - CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/fluxcd/notification-controller/pull/1279
	security-advisories@github.com	https://github.com/fluxcd/notification-controller/releases/tag/v1.8.3
	security-advisories@github.com	https://github.com/fluxcd/notification-controller/security/advisories/GHSA-h9cx-xjg6-5v2w

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Flux notification-controller is the event forwarder and notification dispatcher for the GitOps Toolkit controllers. Prior to 1.8.3, the gcr Receiver type in Flux notification-controller does not validate the email claim of Google OIDC tokens used for Pub/Sub push authentication. This allows any valid Google-issued token, to authenticate against the Receiver webhook endpoint, triggering unauthorized Flux reconciliations. Exploitation requires the attacker to know the Receiver\u0027s webhook URL. The webhook path is generated as /hook/sha256sum(token+name+namespace), where the token is a random string stored in a Kubernetes Secret. There is no API or endpoint that enumerates webhook URLs. An attacker cannot discover the path without either having access to the cluster and permissions to read the Receiver\u0027s .status.webhookPath in the target namespace, or obtaining the URL through other means (e.g. leaked secrets or access to Pub/Sub config). Upon successful authentication, the controller triggers a reconciliation for all resources listed in the Receiver\u0027s .spec.resources. However, the practical impact is limited: Flux reconciliation is idempotent, so if the desired state in the configured sources (Git, OCI, Helm) has not changed, the reconciliation results in a no-op with no effect on cluster state. Additionally, Flux controllers deduplicate reconciliation requests, sending many requests in a short period results in only a single reconciliation being processed. This vulnerability is fixed in 1.8.3."
    }
  ],
  "id": "CVE-2026-40109",
  "lastModified": "2026-04-09T21:16:12.277",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 3.1,
          "baseSeverity": "LOW",
          "confidentialityImpact": "NONE",
          "integrityImpact": "LOW",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 1.6,
        "impactScore": 1.4,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-04-09T21:16:12.277",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/fluxcd/notification-controller/pull/1279"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/fluxcd/notification-controller/releases/tag/v1.8.3"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/fluxcd/notification-controller/security/advisories/GHSA-h9cx-xjg6-5v2w"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-287"
        },
        {
          "lang": "en",
          "value": "CWE-345"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

Sightings

Author	Source	Type	Date

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.

Action not permitted

CVE-2026-40109 (GCVE-0-2026-40109)

GHSA-H9CX-XJG6-5V2W

Impact

Patches

Credits

FKIE_CVE-2026-40109

Tags

Sightings

Nomenclature