Answer in brief
CVE-2026-120306 records a Critical severity (CVSS 9.9) vulnerability in Beta9 build sandbox escape via chroot-only isolation. The current sources do not mark it as known exploited. The current feed maps beam-cloud/github.com/beam-cloud/beta9 (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 9.9. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps beam-cloud/github.com/beam-cloud/beta9 (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| beam-cloud/github.com/beam-cloud/beta9generic | >=0 <0.1.756 | 0.1.756 |
Published upstream
Nov 1, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Nov 1, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Nov 1, 2026
Beta9 turns each shell command in a tenant image definition into a Dockerfile RUN line and executes it with Buildah on the build worker. The worker image sets BUILDAH_ISOLATION=chroot, and no buildah invocation passes --isolation, so the step only changes its filesystem root. It keeps the worker pod's PID, network, IPC, and user namespaces, runs as uid 0, and holds CAP_DAC_OVERRIDE. PID 1 in that procfs is the worker entrypoint, so /proc/1/root is the worker container's filesystem and is writable. That filesystem contains the runc, buildah, and runsc binaries the worker uses to start tenant containers, the worker's Kubernetes service account token, and the host directories mounted into the pod. Worker pods are privileged. Clip v2 layered builds are the default, so a tenant with a workspace token reaches this by submitting one image build. The read-only proof confirmed the shared namespaces, CAP_DAC_OVERRIDE, and that the worker's runc binary is visible at /proc/1/root. Fixed in worker 0.1.756: Buildah RUN steps, including the WORKDIR mkdir, use OCI isolation with private PID, IPC, and network namespaces, and tenant ARG values are passed only into the build container.
Quoted source text, attributed separately from HOL analysis.