CVE-2026-40109Network attack vector

Unauthorized reconciliation via unchecked OIDC email claim

Published Apr 9, 2026 · Updated Apr 9, 2026

Authentication bypass in Flux CD Notification Controller before 1.8.3 allows remote attackers to trigger unauthorized reconciliations. The GCR Receiver accepts any valid Google-issued OIDC token without comparing its email claim to the configured Pub/Sub service account. Exploitation requires the unenumerable webhook URL; reconciliation is idempotent and changes cluster state only when configured source state has changed.

CVSS severity3.1
Low
EPSS probability0.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Flux CD Notification Controller before 1.8.3 allows remote attackers to trigger unauthorized reconciliations. The GCR Receiver accepts any valid Google-issued OIDC token without comparing its email claim to the configured Pub/Sub service account. Exploitation requires the unenumerable webhook URL; reconciliation is idempotent and changes cluster state only when configured source state has changed.

The record

CVE
CVE-2026-40109
Published
Apr 9, 2026
Updated
Apr 9, 2026
Vendor
Flux CD
Product
Notification Controller
Classifications
CWE-287, CWE-345, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.8.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Flux CD · Notification Controllerversion=< 1.8.3

Published CVSS scores

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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-287Improper Authentication
CWE-345Insufficient Verification of Data Authenticity
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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