GHSA-7hp6-g3pq-3pc3 nebula-mesh: Host advanced overrides allow YAML injection into agent config.yml

• Go github.com/juev/nebula-mesh: < 0.3.2 → fixed in 0.3.2

`internal/configgen/generator.go:86,108,119` interpolates the operator-supplied `ListenHost` and `TunDevice` fields raw into a `text/template` that produces the agent's `config.yml`. `internal/web/advanced.go:20-35` accepts both with only `strings.TrimSpace` — no character or shape validation. Exploit An operator (or attacker with any operator key, given the cross-tenant CRUD advisory) sets `adv_tun_device` to: ``` nebula0 lighthouse: am_lighthouse: true hosts: ["10.0.0.1"] ``` The agent fetches the rendered config on its next signed poll. On config reload, it loads the injected YAML keys: the host self-promotes to lighthouse, attracts mesh traffic, or sets `am_relay: true` to be selected as a relay. The `ListenHost` field has the same shape. Affected All released versions prior to v0.3.2. Threat model • Today: operator can compromise their own host's config (trivially allowed if they own the host, but they can also set lighthouse/relay flags that the operator-create form does NOT expose — privilege uplift within their own tenant). • Combined with the critical /api/v1 authz advisory: any operator key can mutate ANOTHER tenant's host overrides and inject YAML there. • Post-fix of the authz advisory: still relevant — the agent unconditionally trusts whatever config the server hands it, so any future operator-impersonation bug re-amplifies this. Suggested fix Two options, either acceptable: 1. Input validation in `parseAdvancedFromForm` (`internal/web/advanced.go`): • `ListenHost`: regex `^[A-Za-z0-9.:\[\]_-]+$` (IPv4/IPv6/hostname) • `TunDevice`: regex `^[A-Za-z0-9_-]{1,15}$` (Linux IFNAMSIZ caps at 15) Reject invalid input with a form-level error; do not write to the host row. 2. Safer marshalling: switch `configgen/generator.go` to marshal a typed Go struct via `gopkg.in/yaml.v3` (which escapes correctly) instead of `text/template` string-concat. Larger change, but eliminates this entire injection class. Option 2 is preferable long-term. Option 1 is the quick fix. The `unsafe_routes` advanced field is already `netip.Parse{Prefix,Addr}`-validated at `enroll.go:226-233` — apply the same validation discipline to the other advanced fields.