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Portainer missing authorization on Docker plugin endpoints, which allows host RCE

Critical severity GitHub Reviewed Published May 10, 2026 in portainer/portainer

Package

gomod github.com/portainer/portainer (Go)

Affected versions

>= 2.33.0, < 2.33.8
>= 2.39.0, < 2.39.2
>= 2.40.0, < 2.41.0

Patched versions

2.33.8
2.39.2
2.41.0

Description

Summary

Portainer enforces Role-Based Access Control (RBAC) on top of the Docker API. The proxy layer routes incoming Docker API requests to per-resource handlers (containers, images, services, volumes, etc.) that apply authorization checks.

The Docker plugin management endpoints (/plugins/*) were not registered with a handler, so standard users with endpoint access could call privileged plugin operations — including installing and enabling plugins — directly against the underlying Docker daemon.

The vulnerability is exposed when a non-admin Portainer user (Standard User role, or any role granted endpoint-level access) has been given access to a Docker endpoint via Portainer RBAC. Administrators and users without Docker endpoint access are not affected.

A regular user with access to a Docker endpoint can:

  • Pull an arbitrary plugin from any registry via POST /plugins/pull.
  • Grant it the privileges it requests, including CAP_SYS_ADMIN and host-path mounts.
  • Enable the plugin via POST /plugins/{name}/enable, at which point Docker runs the plugin with root privileges on the host.

Docker plugins execute as root on the host and can request arbitrary host capabilities and mounts. Enabling a crafted plugin gives the user access to the host filesystem and equivalent to root on the Docker host.

Severity

Critical — CVSS 9.4
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

CWE-862 — Missing Authorization

Affected Versions

The vulnerability exists in every Portainer release where the Docker API proxy uses the prefix-allowlist routing model — /plugins has never been in the allowlist, and the fall-through path has never applied authorization.

Fixes are included in the next release of each supported branch:

Branch First vulnerable Fixed in
2.33.x (LTS) 2.33.0 2.33.8
2.39.x (LTS) 2.39.0 2.39.2
2.40.x (STS) 2.40.0 2.41.0

Portainer LTS branches receive fixes for 6 months plus a 3-month overlap after the next LTS ships. STS releases are supported only until the next STS ships — the 2.40.x STS line ends with the 2.41.0 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 LTS branch.

Workarounds

Administrators who cannot immediately upgrade can reduce exposure by temporarily revoking Docker endpoint access for non-admin users via Portainer RBAC until the patched release is deployed. This eliminates the attack surface without disruption for administrators. This does not replace the fix.

Affected Code

// api/http/proxy/factory/docker/transport.go (pre-fix)

var prefixProxyFuncMap = map[string]func(...){
    "build":      ...,
    "configs":    ...,
    "containers": ...,
    "images":     ...,
    "networks":   ...,
    "nodes":      ...,
    "secrets":    ...,
    "services":   ...,
    "swarm":      ...,
    "tasks":      ...,
    "v2":         ...,
    "volumes":    ...,
}

func (transport *Transport) ProxyDockerRequest(request *http.Request) (*http.Response, error) {
    // ...
    prefix := strings.Split(strings.TrimPrefix(unversionedPath, "/"), "/")[0]

    if proxyFunc := prefixProxyFuncMap[prefix]; proxyFunc != nil {
        return proxyFunc(transport, request, unversionedPath)  // authorized
    }

    return transport.executeDockerRequest(request)  // forwarded without authorization
}

/plugins is not in prefixProxyFuncMap, so requests to plugin endpoints fall through to executeDockerRequest and are forwarded to the Docker daemon without any Portainer-side authorization check.

Impact

An authenticated, non-admin Portainer user with access to any Docker-enabled endpoint can:

  • Install and enable arbitrary Docker plugins from any registry.
  • Execute plugin code with root privileges on the Docker host (including declaring CAP_SYS_ADMIN and host-path mounts).
  • Read and modify files on the host filesystem from a restricted account, overriding the administrator's security policy.

Timeline

  • 2026-03-16: Reported via GitHub Security Advisory by ikkebr.
  • 2026-04-20: Fix merged to develop, release/2.39, and release/2.33.
  • 2026-04-29: 2.41.0 released.
  • 2026-05-07: 2.39.2-LTS and 2.33.8-LTS released.

Credit

  • ikkebr — identified and reported the proxy allowlist bypass affecting the Docker plugin management endpoints.

References

@predlac predlac published to portainer/portainer May 10, 2026
Published to the GitHub Advisory Database May 14, 2026
Reviewed May 14, 2026

Severity

Critical

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 Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality High
Integrity High
Availability High

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:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

EPSS score

Weaknesses

Missing Authorization

The product does not perform an authorization check when an actor attempts to access a resource or perform an action. Learn more on MITRE.

CVE ID

CVE-2026-44848

GHSA ID

GHSA-rrmm-9v76-h3p4

Source code

Credits

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