CVE-2026-120307: Beta9 worker Path Traversal (CVSS 9.9)

Description

The Beta9 worker serves the sandbox file API from outside the container. getHostPathFromContainerPath turns the tenant's container path into a worker path. If the unresolved path starts with a mount destination, including the default upload mount at /tmp/.beta9, the remainder is joined onto that mount's source with filepath.Join, which cleans parent-directory segments after the prefix check. A long enough run of those segments names any absolute path on the worker. A path that matches no mount is joined onto the container root and opened in the worker's own filesystem, so an absolute symbolic link such as /var/run pointing at /run is followed against the worker root. Upload, download, stat, list, find-in-files, replace-in-files, and delete-file all call this helper. A tenant with a workspace token and one running sandbox can read, write, list, and delete files on the hosting worker as root, including files of other tenants on that machine. A read-only proof downloaded the worker pod's Kubernetes service account token through the file API for a path that did not exist inside the sandbox. In the shipped remote-node manifests that service account is bound to cluster-admin. Fixed in worker 0.1.756: sandbox file operations and workspace sync open paths with os.OpenRoot, so parent-directory and symlink lookups stay inside the container root or the mount source.

Metrics

CVSS 3.1

9.9/10

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

Weakness Enumeration

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
beam-cloud	Beta9 worker	< 0.1.756

References

Timeline

Published: Nov 1, 2026
Last Modified: Nov 1, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-120307?

The Beta9 worker serves the sandbox file API from outside the container. getHostPathFromContainerPath turns the tenant's container path into a worker path. If the unresolved path starts with a mount destination, including the default upload mount at /tmp/.beta9, the remainder is joined onto that mount's source with filepath.Join, which cleans parent-directory segments after the prefix check. A long enough run of those segments names any absolute path on the worker. A path that matches no mount is joined onto the container root and opened in the worker's own filesystem, so an absolute symbolic link such as /var/run pointing at /run is followed against the worker root. Upload, download, stat, list, find-in-files, replace-in-files, and delete-file all call this helper. A tenant with a workspace token and one running sandbox can read, write, list, and delete files on the hosting worker as root, including files of other tenants on that machine. A read-only proof downloaded the worker pod's Kubernetes service account token through the file API for a path that did not exist inside the sandbox. In the shipped remote-node manifests that service account is bound to cluster-admin. Fixed in worker 0.1.756: sandbox file operations and workspace sync open paths with os.OpenRoot, so parent-directory and symlink lookups stay inside the container root or the mount source.

How severe is CVE-2026-120307?

CVE-2026-120307 has a CVSS score of 9.9/10 (CRITICAL severity).

How do I fix CVE-2026-120307?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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