{"id":"CVE-2026-120307","title":"Beta9 container escape via unvalidated sandbox file paths","summary":"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 upl…","severity":"critical","cvss":9.9,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H","cvssSource":"cna","cwe":["CWE-22","CWE-23","CWE-59"],"vendor":"beam-cloud","product":"github.com/beam-cloud/beta9","affected":["github.com/beam-cloud/beta9 < 0.1.756"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-11-02T19:46:03.614684Z"},"published":"2026-11-01","updated":"2026-11-02","sourceUpdated":"2026-11-02T19:46:38.442Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-120307","references":[{"url":"https://github.com/beam-cloud/beta9","label":"Beta9 repository"},{"url":"https://github.com/beam-cloud/beta9/pull/1897","label":"Handle sandbox edge cases (fix pull request)"},{"url":"https://github.com/beam-cloud/beta9/commit/a28bf12cf0007c792a25d8ed282b4e8bf6f30393","label":"Fix commit a28bf12"},{"url":"https://github.com/beam-cloud/beta9/releases/tag/worker-0.1.756","label":"worker-0.1.756"}],"tags":["cve.org"],"epss":0.00484,"epssPercentile":0.41811,"ingestedAt":"2026-11-05T19:30:42.811Z","slug":"CVE-2026-120307","body":"## Overview\n\nThe 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.\n\n## Affected\n\n- `github.com/beam-cloud/beta9 < 0.1.756`\n\n## Remediation\n\nUpgrade the Beta9 worker to 0.1.756 or later. Sandbox file APIs and workspace sync use os.OpenRoot, so parent-directory segments and symbolic links stay inside the container root or the mount source. File operations refuse read-only mounts and do not write through a symlink swapped in after path resolution. The fix is commit a28bf12 (pull request 1897), released as worker-0.1.756 on 2026-09-15.","depth":"midnight","depthScore":55,"depthScoreParts":{"impact":54.5,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}