Read-only volume remount bypass via guest CAP_SYS_ADMIN

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.

Source published

16 May 2026 12:00:00 UTC

Source modified

12 Oct 2026 18:00:13 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

OSV · upstream source license applies

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CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H