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

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Summary

CVECVE-2026-40109
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-09 21:16:12 UTC
Updated2026-04-16 14:42:01 UTC
DescriptionFlux 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.

Risk And Classification

Primary CVSS: v3.1 3.1 LOW from [email protected]

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

EPSS: 0.000120000 probability, percentile 0.016520000 (date 2026-04-16)

Problem Types: CWE-287 | CWE-345 | CWE-287 CWE-287: Improper Authentication | CWE-345 CWE-345: Insufficient Verification of Data Authenticity

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary3.1LOWCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N
3.1CNADECLARED3.1LOWCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Fluxcd Notification-controller affected < 1.8.3 Not specified

References

ReferenceSourceLinkTags
github.com/fluxcd/notification-controller/pull/1279 [email protected] github.com
github.com/fluxcd/notification-controller/releases/tag/v1.8.3 [email protected] github.com
github.com/fluxcd/notification-controller/security/advisories/GHSA-h9cx-... [email protected] github.com
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