The Flux Operator is a Kubernetes CRD controller that manages the lifecycle of CNCF Flux CD and the ControlPlane enterprise distribution. Starting in version 0.36.0 and prior to version 0.40.0, a privilege escalation vulnerability exists in the Flux Operator Web UI authentication code that allows an attacker to bypass Kubernetes RBAC impersonation and execute API requests with the operator's service account privileges. In order to be vulnerable, cluster admins must configure the Flux Operator with an OIDC provider that issues tokens lacking the expected claims (e.g., email, groups), or configure custom CEL expressions that can evaluate to empty values. After OIDC token claims are processed through CEL expressions, there is no validation that the resulting username and groups values are non-empty. When both values are empty, the Kubernetes client-go library does not add impersonation headers to API requests, causing them to be executed with the flux-operator service account's credentials instead of the authenticated user's limited permissions. This can result in privilege escalation, data exposure, and/or information disclosure. Version 0.40.0 patches the issue.
CVE-2026-23990
“—” beside the score: it is equal to NVD's CVSS score.
Score 5.3 from GitHub Security Advisory (severity: MODERATE) published 2026-01-21. NVD baseline CVSS 5.3; sources differ by 0.0.
Also known asEUVD-2026-4140 (ENISA EUVD) · GHSA-4xh5-jcj2-ch8q (GitHub Security Advisories) · GO-2026-4351 (OSV.dev)Source: ENISA EUVD
- Lower severity and no public exploit yet
A fix is available — apply it.
- CVSS v3
- 5.3
- EG Score
- 5.3MEDIUMmedium confidence
- EG Risk
- 24EG Risk 24/100
EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.
How it’s computed (value × EchelonGraph’s weight)Severity53% × 45%Impact severity (EG Severity): CVSS 5.3 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation0.4% × 40%FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.Automatability0% × 15%CISA's SSVC Automatable value: no (Vulnrichment).SSVC (CISA's decision table, applied by EchelonGraph): Track at every mission impact level.Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.Action: A fix is available. Apply it within your standard update timelines. - EPSS PROB
- 0.3%
- EPSS %ILE
- 28th
- KEV
- Not listed
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (5.3): severity, escalated by confirmed exploitation. This CVE's 5.3 is its impact severity (EG Severity), not escalated.
- EG Severity
- 5.3 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.3% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-31). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.
A fix is available. Apply it within your standard update timelines.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it
Published
January 21, 2026
Last Modified
June 17, 2026
Advisory Details (4)
Auto-updated Aug 9, 2026Web UI Impersonation Bypass via Empty OIDC Claims · Advisory · controlplaneio-fluxcd/flux-operator · GitHub
https://github.com/controlplaneio-fluxcd/flux-operator/security/advisories/GHSA-4xh5-jcj2-ch8qv0.40.0
Patch available: controlplaneio-fluxcd/flux-operator v0.40.0
https://github.com/controlplaneio-fluxcd/flux-operator/releases/tag/v0.40.0web: strict validation for RBAC impersonation
Fix merged in controlplaneio-fluxcd/flux-operator PR #610 on 2026-01-20 — awaiting tagged release
https://github.com/controlplaneio-fluxcd/flux-operator/pull/610commit 084540424f6d (controlplaneio-fluxcd/flux-operator)
Fix landed in controlplaneio-fluxcd/flux-operator commit 084540424f6d — awaiting tagged release
https://github.com/controlplaneio-fluxcd/flux-operator/commit/084540424f6de8ba5d88fb1fd1e8472ba29afd7ePatch Availability(1)
| Vendor / Ecosystem | Fix (by version range) / Patch | Released | Source |
|---|---|---|---|
| go | github.com/controlplaneio-fluxcd/flux-operator @ 0.40.0 (fixes >= 0.36.0, < 0.40.0) | — | ghsa |
Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.
Affected Packages
(1 across 1 ecosystem)
Go(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| github.com/controlplaneio-fluxcd/flux-operator | — |
| — |
Weakness Classification(2)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 10× in last 7d / 40× in last 30d)
Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.
Showing the most recent 99 of 208 refreshes on record for this CVE.
A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 1 repeat row among the latest 100 is merged into the row it repeats. The 109 oldest rows on record are not shown and were not checked, so the counts can still include repeats.
- 2026-11-01 16:34 UTCEPSS rescoreEPSS 0.3% · 28th percentile
- 2026-11-01 07:57 UTCGHSA enrichmentGHSA-4xh5-jcj2-ch8q · GitHub severity MODERATE · GitHub CVSS 5.3
- 2026-11-01 07:57 UTCEG score recompute
- 2026-10-31 16:32 UTCEPSS rescoreEPSS 0.3% · 28th percentile
- 2026-10-31 02:55 UTCOSV refresh
- 2026-10-30 16:34 UTCEPSS rescoreEPSS 0.3% · 28th percentile
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- 2026-10-25 16:32 UTCEPSS rescoreEPSS 0.3% · 28th percentile
- 2026-10-25 14:41 UTCEG score recompute
- 2026-10-24 16:32 UTCEPSS rescoreEPSS 0.3% · 27th percentile
- 2026-10-23 16:31 UTCEPSS rescoreEPSS 0.3% · 27th percentile
- 2026-10-23 04:57 UTCEG score recompute
- 2026-10-22 16:34 UTCEPSS rescoreEPSS 0.3% · 27th percentile
- 2026-10-21 16:32 UTCEPSS rescoreEPSS 0.3% · 27th percentile
- 2026-10-20 16:32 UTCEPSS rescoreEPSS 0.3% · 26th percentile
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- 2026-10-18 16:31 UTCEPSS rescoreEPSS 0.3% · 26th percentile
- 2026-10-18 03:54 UTCEG score recompute
- 2026-10-17 16:33 UTCEPSS rescoreEPSS 0.3% · 26th percentile
- 2026-10-16 16:41 UTCEPSS rescoreEPSS 0.4% · 27th percentile
- 2026-10-15 16:31 UTCEPSS rescoreEPSS 0.4% · 27th percentile
- 2026-10-14 16:32 UTCEPSS rescoreEPSS 0.4% · 27th percentile
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- 2026-10-13 16:33 UTCEPSS rescoreEPSS 0.4% · 27th percentile
- 2026-10-12 16:33 UTCEPSS rescoreEPSS 0.4% · 26th percentile
- 2026-10-12 16:20 UTCEG score recompute
- 2026-10-11 20:02 UTCEG score recompute
- 2026-10-11 17:15 UTCEG score recompute
- 2026-10-11 14:47 UTCEG score recompute
- 2026-10-11 13:48 UTCEPSS rescoreEPSS 0.4% · 26th percentile
- 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.4% · 26th percentile
- 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.4% · 26th percentile
- 2026-10-08 19:56 UTCOSV refresh
- 2026-10-08 17:11 UTCEPSS rescoreEPSS 0.4% · 26th percentile
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- 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.4% · 26th percentile
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- 2026-09-24 14:03 UTCEPSS rescoreEPSS 0.4% · 26th percentile
- 2026-09-20 20:15 UTCEPSS rescoreEPSS 0.4% · 28th percentile
- 2026-09-19 02:00 UTCOSV refresh
- 2026-09-18 19:27 UTCEPSS rescoreEPSS 0.4% · 28th percentile
- 2026-09-16 14:07 UTCEPSS rescoreEPSS 0.3% · 25th percentile
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- 2026-09-01 04:39 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
- 2026-08-31 05:49 UTCOSV refresh
- 2026-08-30 19:17 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
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- 2026-08-28 21:41 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
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- 2026-08-23 00:19 UTCEPSS rescoreEPSS 0.3% · 24th percentile
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- 2026-08-15 01:30 UTCEPSS rescoreEPSS 0.3% · 22nd percentile
- 2026-08-14 13:12 UTCEG score recompute
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- 2026-08-08 00:03 UTCEG score recompute
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- 2026-07-31 13:42 UTCOSV refresh
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Frequently asked(5)
What is CVE-2026-23990?
When was the CVE record for CVE-2026-23990 published?
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What is the CVSS score of CVE-2026-23990?
How do I remediate CVE-2026-23990?
Dependency Blast Radius
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