Newline injection in LXD NVIDIA instance configuration handling (CVE-2026-63298)

LXD's `nvidia.driver.capabilities` instance configuration key uses the `validate.IsAny` validator, which accepts any input without filtering, allowing newline characters to pass through unsanitized into the generated `lxc.conf` file. An authenticated attacker with permission to set instance configuration can inject arbitrary LXC directives - including `lxc.hook.pre-start` - which execute as root on the host when the container starts. This is an independent bypass of CVE-2026-23953, which added newline filtering only for `environment.*` keys and left `nvidia.driver.capabilities` unaddressed. Affected versions: - >= 4.0, <= 6.9 We recommend updating to: 4.0.12, 5.0.8, 5.21.6. CVSS 9.9 · our assessment: act_now Reference: https://github.com/canonical/lxd/security/advisories/GHSA-vfh7-q59q-54v2 Details: https://vuln.today/cve/CVE-2026-63298