CVE-2026-44882

Portainer proxies requests to Kubernetes clusters through a middleware layer (kubeClientMiddleware) that validates the requesting user's token before forwarding traffic to the cluster. When security.RetrieveTokenData returned an error, the middleware wrote an HTTP 403 response but was missing a return statement, execution continued into the handler with a nil tokenData value.

The Kubernetes endpoints sit behind Portainer's outer AuthenticatedAccess bouncer, so an attacker requires a valid Portainer session. However, a user whose secondary token validation fails in kubeClientMiddleware, for example a user without permission to access a given Kubernetes endpoint, would have their request forwarded to the cluster anyway, bypassing the authorization check. The same defect was present in both the CE and EE codebases.

Severity

High
CWE-863, Incorrect Authorization

Privilege required is Low, any valid Portainer session is sufficient to reach the middleware. Once the authorization outcome is bypassed, the attacker can read and modify Kubernetes resources on the target endpoint that their role should not permit, confidentiality and integrity impact are both High. No availability impact is introduced directly.

Affected Versions

The missing return statement has been present since Kubernetes proxy support was introduced.

Portainer 2.39.0 and later are not affected, the fix was present from the initial 2.39.0 release. All releases prior to 2.33.0 are end-of-life and will not receive a fix; users on EOL versions should upgrade to a supported release.

Workarounds

There is no configuration change that prevents the bypass directly. Administrators who cannot immediately upgrade can reduce exposure by:

• Restricting Kubernetes endpoint access. Remove Portainer access to Kubernetes endpoints for users who do not require it. A user without endpoint access cannot reach kubeClientMiddleware.
• Auditing Kubernetes RBAC. Ensure the service account Portainer uses to proxy cluster requests carries least-privilege RBAC permissions, this limits the blast radius if the bypass is exploited.

Neither of these replaces the fix.

Affected Code

kubeClientMiddleware in api/http/handler/kubernetes/handler.go wrote the error response but did not return, allowing execution to continue with nil tokenData:

// api/http/handler/kubernetes/handler.go (pre-fix, CE and EE)
tokenData, err := security.RetrieveTokenData(r)
if err != nil {
    httperror.WriteError(w, http.StatusForbidden,
        "permission denied to access the environment", err)
    // missing return, tokenData is nil, execution continues
}

// tokenData.ID dereferenced on the next line:
_, ok := handler.KubernetesClientFactory.GetProxyKubeClient(
    strconv.Itoa(endpointID), strconv.Itoa(int(tokenData.ID)))

The fix adds a single return after the WriteError call in both CE and EE:

// post-fix
if err != nil {
    httperror.WriteError(w, http.StatusForbidden,
        "permission denied to access the environment", err)
    return
}

Timeline

• 2026-02-16: Fix merged to develop.
• 2026-02-25: 2.39.0 released with fix.
• 2026-05-07: 2.33.8 released with backport fix.

• Kubernetes authorization bypass. A low-privileged Portainer user can reach Kubernetes API endpoints on environments their role does not permit, with the proxy client of the legitimate session used as the vehicle.
• Cluster resource access. Depending on the service account permissions Portainer holds on the cluster, the attacker can read or modify namespaced resources, including pods, secrets, config maps, and deployments.
• Potential for lateral movement. Kubernetes secrets readable through this path may contain credentials for other services within the cluster or the broader infrastructure.

The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.

CVE-2026-44882 has a CVSS score of 8.1 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.33.8); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-44882? CVE-2026-44882 is a high-severity incorrect authorization vulnerability in github.com/portainer/portainer (go), affecting versions >= 2.33.0, < 2.33.8. It is fixed in 2.33.8. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
2. How severe is CVE-2026-44882? CVE-2026-44882 has a CVSS score of 8.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/portainer/portainer are affected by CVE-2026-44882? github.com/portainer/portainer (go) versions >= 2.33.0, < 2.33.8 is affected.
4. Is there a fix for CVE-2026-44882? Yes. CVE-2026-44882 is fixed in 2.33.8. Upgrade to this version or later.
5. Is CVE-2026-44882 exploitable, and should I be worried? Whether CVE-2026-44882 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-44882 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-44882? Upgrade github.com/portainer/portainer to 2.33.8 or later.