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Default kuma-cp leaks admin token cross-origin via CORS wildcard + LocalhostIsAdmin

Moderate severity GitHub Reviewed Published May 9, 2026 in kumahq/kuma • Updated May 14, 2026

Package

gomod github.com/kumahq/kuma (Go)

Affected versions

< 2.7.25
>= 2.9.0, < 2.9.15
>= 2.11.0, < 2.11.13
>= 2.12.0, < 2.12.10
>= 2.13.0, < 2.13.5

Patched versions

2.7.25
2.9.15
2.11.13
2.12.10
2.13.5

Description

Summary

Default kuma-cp config leaks the admin bootstrap token and signing keys to any webpage the operator visits while the control plane is reachable from their browser. CorsAllowedDomains: [".*"] reflects any Origin, and LocalhostIsAdmin: true promotes requests from 127.0.0.1 to mesh-system:admin. A cross-origin fetch() from a malicious page returns the admin JWT and signing material.

Am I affected?

You are affected if all of these hold:

  1. kuma-cp runs with default config (CorsAllowedDomains: [".*"] and LocalhostIsAdmin: true).
  2. The control plane is reachable from a browser on the same machine:
    • kuma-cp run on a developer laptop
    • Docker --network host or port-publish on a workstation
    • kubectl port-forward from a machine that also browses the web
  3. The operator visits a page running attacker JavaScript while the control plane is reachable.

You are not affected if:

  • The control plane runs on a Kubernetes cluster accessed via ClusterIP, NodePort, or LoadBalancer from a remote client.
  • The control plane runs on an SSH-administered VM with no browser on the host.
  • KUMA_API_SERVER_AUTHN_LOCALHOST_IS_ADMIN=false is set (see https://kuma.io/docs/latest/production/secure-deployment/api-server-auth/).
  • KUMA_API_SERVER_CORS_ALLOWED_DOMAINS is set to an explicit allowlist that excludes attacker origins.

Mitigation

  1. Set KUMA_API_SERVER_AUTHN_LOCALHOST_IS_ADMIN=false after retrieving the admin token.
  2. Set KUMA_API_SERVER_CORS_ALLOWED_DOMAINS to an explicit allowlist, for example http://localhost:5681,http://127.0.0.1:5681.
  3. Do not run kuma-cp on a machine where you browse untrusted sites.

Fix

Fixed in #16416, backported to all supported release branches (#16423, #16424, #16425, #16426, #16427).

Changes in patched versions:

  • CorsAllowedDomains default changed from [".*"] to [] — CORS is now opt-in; set the env var explicitly if you need GUI access.
  • LocalhostIsAdmin hardened: now requires direct loopback RemoteAddr and Host, and rejects requests carrying proxy-hop headers (X-Forwarded-For), cross-site fetch metadata (Sec-Fetch-Site), or a non-localhost Origin.

Upgrade to a patched version:

  • 2.7.25
  • 2.9.15
  • 2.11.13
  • 2.12.10
  • 2.13.5

Credits

Reported by eldudareeno.

CVSS

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N = 5.1 Medium.

References

@bartsmykla bartsmykla published to kumahq/kuma May 9, 2026
Published to the GitHub Advisory Database May 14, 2026
Reviewed May 14, 2026
Last updated May 14, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction Active
Vulnerable System Impact Metrics
Confidentiality Low
Integrity Low
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

EPSS score

Weaknesses

Origin Validation Error

The product does not properly verify that the source of data or communication is valid. Learn more on MITRE.

Permissive Cross-domain Security Policy with Untrusted Domains

The product uses a web-client protection mechanism such as a Content Security Policy (CSP) or cross-domain policy file, but the policy includes untrusted domains with which the web client is allowed to communicate. Learn more on MITRE.

CVE ID

CVE-2026-45021

GHSA ID

GHSA-3vcp-chfh-f6r2

Source code

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