GHSA-mc5q-6hpj-rp7j

### Summary

The Twig content sandbox replaces `config` with the redacted `SandboxConfig` facade and strips `Config::get`/`toArray` from the method allowlist (GHSA-j274-39qw-32c9), so editor content can't read config secrets via `config`. That's bypassable: `grav` is the raw container, `offsetget` is allow-listed on it, so `grav.offsetGet('config')` returns the real `Config`. The allow-listed filters `json_encode`/`print_r`/`yaml_encode` then serialize it at the PHP level, never hitting the sandbox method gate, dumping the whole config tree including every `plugins.*` secret (SMTP creds, API keys, plugin DB creds). Incomplete fix for GHSA-j274-39qw-32c9. `security.salt` does not leak (it lives outside config).

### Details

The documented path is blocked: `config` is the `SandboxConfig` facade (`Twig.php:660`) and the raw `Config`/`Data` method entries are stripped when `config_access` is false, so `{{ config.get(...) }}` returns the default and `{{ grav.offsetGet('config').get(...) }}` raises `SecurityNotAllowedMethodError`.

The bypass uses two allow-listed primitives the redaction doesn't cover:

1. `grav.offsetGet('config')` returns the raw `Config`. The `SandboxConfig` facade replaces only the `config` variable, not `grav['config']`; `offsetget` is allow-listed on `Grav\Common\Grav` in `system/config/security.yaml`. 2. `json_encode`/`print_r`/`yaml_encode` serialize the object inside the filter and never call `GravSecurityPolicy::checkMethodAllowed` (`GravSecurityPolicy.php:65`), so the stripped methods don't matter.

Bug class: object-dumping filters bypass the sandbox member gate. The same dump reaches `page`/`pages`/`uri`/`user` via their allow-listed accessors; `config` is the secret-bearing target.

Reachable below the publisher-Twig opt-in: a `_`-prefixed slug is modular (`Page.php:228`), and `Page::content()` sets `$process_twig = $scan_twig_xss || $this->modularTwig()` (`Page.php:816`), so a modular child's body Twig is sandboxed-rendered even with `twig_content.process_enabled` false (the default), while `$scan_twig_xss` stays false so the render-time XSS scan (GHSA-2c4f-86xc-cr74) is skipped. Any `admin.pages` author (or filesystem write to `user/pages`) exfiltrates config on a stock install. On a regular `process.twig` page the whole-tree dump trips the XSS scan and is blanked, but a targeted `split`/`slice` extraction of one subtree is XSS-clean and survives.

### PoC

Sandboxed render, `config_access` default false. First two lines show the gate holding, third is the bypass:

```twig {{ config.get('plugins.email.mailer.smtp.password', 'DENIED') }} {# => DENIED #} {{ grav.offsetGet('config').get('plugins.email.mailer.smtp.password') }} {# => SecurityNotAllowedMethodError 'get' #} {{ grav.offsetGet('config')|json_encode }} {# => {...,"plugins":{"email":{"mailer":{"smtp":{"password":"CANARY..."}}}},...} #} ```

Stock-install reproduction (no `user/config/security.yaml`):

```yaml # user/config/plugins/email.yaml -- decoy secret mailer: { smtp: { password: CANARY_SMTP_PW_8b3f1 } } ```

``` # user/pages/70.parent/default.md --- title: Parent content: { items: '@self.modular' } template: modular --- ```

```twig {# user/pages/70.parent/_secret/default.md #} --- title: Secret template: modular/text --- {{ grav.offsetGet('config')|json_encode }} ```

```bash curl -s http://localhost/parent # body contains CANARY_SMTP_PW_8b3f1 ```

`logs/security.log` shows no sandbox block and no XSS scan for the route. Verified on Grav 2.0.1 (6f619f0ae), PHP 8.4.22, Twig 3.26.1-DEV.

### Impact

A page author (`admin.pages`, no admin/super) reads the entire config tree: plugin SMTP credentials, API keys, plugin DB credentials. Read-only. Default install; the modular path needs no Twig opt-in.

### Fix

`system/config/security.yaml`: drop `offsetget` (and `__get`) from `twig_sandbox.allowed_methods` for `Grav\Common\Grav` -- the legit uses are `theme`/`getversion`; `offsetget` is the raw-container reach. Closes the demonstrated path.

Sandbox-wide: make `json_encode`/`print_r`/`yaml_encode`/`string` refuse non-allow-listed objects when `$env->isSandboxed()` (mirror the Closure-only guard Twig applies to `map`/`filter`/`reduce`). Closes the class for `page`/`pages`/`uri`/`user` too.