Vulnerability RUSTSEC-2026-0147
Summary
Read-only volume remount bypass via guest CAP_SYS_ADMIN
Details
Affected versions of boxlite mount host directories shared via virtiofs as guest-side read-only by setting MS_RDONLY from the guest. Because the default guest capability set included CAP_SYS_ADMIN, untrusted code running inside a sandbox could execute mount -o remount,rw <path> to re-flag the share as read-write and then write through to the host filesystem — fully escaping the read-only contract boxlite advertised to callers.
The fix in v0.9.0 enforces read-only at the hypervisor level via krun_add_virtiofs3 (so the guest's MS_RDONLY is no longer the authoritative gate) and drops CAP_SYS_ADMIN from the default guest capability set (matching Docker's defaults).
This is a sandbox-escape bug: boxlite is a sandboxing runtime, so the read-only invariant is part of its security contract. CVSS rated 10.0 by the upstream advisory.
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