HCSEC-2026-19 - Nomad Docker driver vulnerable to host namespace bypass on Linux

Security
1

Bulletin ID: HCSEC-2026-19

Affected Products / Versions: Nomad and Nomad Enterprise up to 2.0.3; fixed in Nomad 2.0.4 and Nomad Enterprise 2.0.4, 1.11.8, and 1.10.14.

Publication Date: July 8, 2026

Summary

HashiCorp Nomad and Nomad Enterprise did not enforce the allow_privileged restriction for the Docker task driver’s host namespace mode options. This may allow an authenticated job submitter to run a container in a host namespace and access information belonging to the host or to other workloads on the same client. This vulnerability, CVE-2026-14373, is fixed in Nomad Community Edition 2.0.4 and Nomad Enterprise 2.0.4, 1.11.8, and 1.10.14.

Background

The Nomad Docker task driver runs workloads as containers on a client node. The driver supports Linux namespace mode options, including the process (PID), IPC, user, and UTS namespace modes, that can place a container in the host’s namespace instead of an isolated one. Nomad’s documentation states that these host namespace modes require the client’s allow_privileged driver option to be enabled.

Details

The Docker task driver passed the process, IPC, user, and UTS namespace mode options from a submitted job to the Docker daemon without enforcing the allow_privileged restriction described in its documentation. As a result, an authenticated user able to submit Docker driver jobs could place a container in a host namespace even on clients where allow_privileged was disabled. Running a task in the host process namespace, for example, allows the container to enumerate host processes and read their environment, which may expose sensitive information such as tokens or credentials held by the Nomad agent or by other allocations on the same client. Exploitation requires the ability to submit Docker driver jobs to the cluster. These host namespace modes are specific to Linux, so the issue affects Linux clients running Linux containers; Windows container workloads are not affected.

Remediation

Customers should evaluate the risk associated with this issue and consider upgrading to Nomad Community Edition 2.0.4 or Nomad Enterprise 2.0.4, 1.11.8, and 1.10.14. Nomad Enterprise customers that are unable to upgrade can implement a Sentinel policy to restrict host namespaces for Docker tasks. The following policy restricts host namespaces:

check_task_config = func(task) {
  if task.driver == "docker" {
    if task.config.ipc_mode is defined and task.config.ipc_mode is "host" {
      return false
    }
    if task.config.pid_mode is defined and task.config.pid_mode is "host" {
      return false
    }
    if task.config.uts_mode is defined and task.config.uts_mode is "host" {
      return false
    }
    if task.config.userns_mode is defined and task.config.userns_mode is "host" {
      return false
    }
  }
  return true
}
restrict_host_namespaces = rule {
  all job.task_groups as tg {
    all tg.tasks as task {
      check_task_config(task)
    }
  }
}
main = rule {
  restrict_host_namespaces

This policy can be applied to Nomad Enterprise clusters with: nomad sentinel apply -level hard-mandatory -scope=submit-job restrict-host-namespace ./policy.hcl.

Acknowledgement

This issue was reported to HashiCorp by Deniz Onur Duzgun (@dduzgun-security).

We deeply appreciate any effort to coordinate disclosure of security vulnerabilities. For information about security at HashiCorp and the reporting of security vulnerabilities, please see https://hashicorp.com/security.