VulnerabilityPublished 21 Jan 2026

CVE-2026-23990: controlplaneio-fluxcd flux-operator · Improper Privilege Management

Affects controlplaneio-fluxcd flux-operatorSource CVE Database V5

Not known to be exploited · CVSS 5.3 Medium : upgrade to 0.40.0 when convenient.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 28% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 0.40.0

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

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

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 21 Jan 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade flux-operator and controlplaneio-fluxcd/flux-operator to 0.40.0.

Affected software

Product	Affected	Fixed in
controlplaneio-fluxcdflux-operator	Affected >=0.36.0 <0.40.0	Fixed in 0.40.0
GitHubcontrolplaneio-fluxcd/flux-operator`pkg:github/controlplaneio-fluxcd/flux-operator`Other threats	Affected >=0.36.0 <0.40.0	Fixed in 0.40.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

European organizations should immediately audit their Kubernetes clusters to identify Flux Operator versions in use and upgrade to version 0.40.0 or later, where the vulnerability is patched. Administrators must review OIDC provider configurations to ensure tokens include all expected claims such as 'email' and 'groups'. Avoid using custom CEL expressions that can evaluate to empty values for username or groups. Implement strict validation of token claims before processing to prevent empty impersonation fields. Additionally, restrict access to the Flux Operator Web UI to trusted users only, and monitor API request logs for anomalous behavior indicative of privilege escalation attempts. Employ Kubernetes audit logging and alerting on service account privilege usage anomalies. Consider implementing network segmentation and zero-trust principles to limit the potential blast radius of compromised operator credentials. Regularly review and tighten RBAC policies associated with the flux-operator service account to minimize privileges to the least necessary.

Description

CVE-2026-23990 is a medium-severity privilege escalation vulnerability in the Flux Operator versions 0.36.0 to before 0.40.0. It arises from improper privilege management in the Web UI authentication code when configured with certain OIDC providers issuing tokens missing expected claims or with custom CEL expressions that yield empty username and groups values. This causes Kubernetes client-go to omit impersonation headers, resulting in API requests executing with the operator's service account privileges rather than the limited authenticated user permissions. Exploitation can lead to privilege escalation and data exposure within Kubernetes clusters using the affected Flux Operator versions. The vulnerability is patched in version 0.40.

Impact

For European organizations using Kubernetes clusters managed by the Flux Operator versions between 0.36.0 and before 0.40.0, this vulnerability poses a significant risk of privilege escalation. Attackers exploiting this flaw can bypass Kubernetes Role-Based Access Control (RBAC) impersonation, gaining elevated privileges equivalent to the operator's service account. This can lead to unauthorized access to sensitive cluster resources, data exposure, and potential lateral movement within the infrastructure. Given the widespread adoption of Kubernetes and Flux CD in cloud-native environments across Europe, organizations relying on these tools for continuous deployment and cluster management may face increased risk of insider threats or external attackers leveraging compromised credentials. The vulnerability's reliance on misconfigured OIDC providers or custom CEL expressions means that organizations with complex or customized authentication setups are particularly vulnerable. The impact is heightened in sectors with strict data protection regulations such as finance, healthcare, and critical infrastructure, where unauthorized access could lead to regulatory penalties and reputational damage.

CWE-269Improper Privilege Management (opens in a new tab)
Class weaknessLikelihood of exploit: MediumOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
Architecture and Design · Operation
Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software.
Architecture and Design · Separation of Privilege
Follow the principle of least privilege when assigning access rights to entities in a software system.
Architecture and Design · Separation of Privilege
Consider following the principle of separation of privilege. Require multiple conditions to be met before permitting access to a system resource.
OWASP Cheat Sheets
Docker Security (opens in a new tab)
Third Party Javascript Management (opens in a new tab)
Virtual Patching (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V1.4.4 (opens in a new tab)
V1.4.5 (opens in a new tab)
V1.10.1 (opens in a new tab)
Attack patterns
Restful Privilege Elevation (opens in a new tab)
Privilege Abuse (opens in a new tab)
Privilege Escalation (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-862Missing Authorization (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #4OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product does not perform an authorization check when an actor attempts to access a resource or perform an action.
Architecture and Design
Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries.
Architecture and Design
Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.8 (opens in a new tab)
V13.4.2 (opens in a new tab)
V7.2.2 (opens in a new tab)
Attack patterns
Exploitation of Thunderbolt Protection Flaws (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 29 Jan 2026, 08:48 UTC

WeaknessesCWE-269, CWE-862

Technical details

References

Community reviews

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