{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "getgrav/grav"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.0.0-beta.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-42842"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-05T21:24:45Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nA Stored Cross-Site Scripting (XSS) vulnerability exists in the Grav CMS Form plugin\u0027s select field template. Taxonomy tag and category values are rendered with the Twig `|raw` filter in the admin panel, bypassing the global autoescape protection. An editor-level user can inject arbitrary JavaScript that executes in any administrator\u0027s browser session when they view or edit any page in the admin panel.\n\nAdditionally, Grav\u0027s built-in XSS detection (`Security::detectXss()`) can be bypassed by using payloads that close the `\u003coption\u003e/\u003cselect\u003e` context and use unquoted event handlers - the `on_events` regex fails to match event handlers without quotes or trailing spaces before `\u003e`.\n\n### Important\n\n- The vulnerability is in the Form plugin (`select.html.twig`), which is installed by default with Grav\n- The XSS is cross-page: a malicious taxonomy value on one page executes when an admin edits any page, because taxonomy options are rendered from a shared global pool\n- An editor can exploit this without any other vulnerability - taxonomy fields are not in the server-side restricted fields list\n- The `HttpOnly` flag on session cookies prevents direct session theft, but the XSS can steal the admin nonce and perform privileged actions via JavaScript\n\n### Permissions Needed\n\n- Editor: can create or edit pages and set taxonomy tag/category values\n\n### Details\n\nThe Form plugin\u0027s select field template renders option values using the `|raw` Twig filter, which outputs content without HTML escaping:\n\nFile: `user/plugins/form/templates/forms/fields/select/select.html.twig`\n\n```twig\n{# Line 55 #}\n avalue|raw \n\n{# Line 65 #}\n suboption|t|raw \n\n{# Line 72 #}\n item_value|t|raw \n```\n\nThe taxonomy field in the page editor uses this select template. When a page has taxonomy values (tags, categories), these values are populated as `\u003coption\u003e` elements in the select dropdown. The `value` attribute is properly escaped by the browser\u0027s attribute encoding, but the **display text** between `\u003coption\u003e` tags is rendered raw:\n\n```html\n\u003coption value=\"\u0026lt;script\u0026gt;alert(1)\u0026lt;/script\u0026gt;\"\u003e\u003cscript\u003ealert(1)\u003c/script\u003e\u003c/option\u003e\n```\n\nSince taxonomy options are collected globally across all pages (to provide autocomplete/selection), a malicious taxonomy value on any page will appear in the taxonomy dropdown of every page editor - making this a cross-page stored XSS.\n\nThe server-side field restriction in the flex-objects plugin only blocks `[\u0027form\u0027, \u0027forms\u0027, \u0027process\u0027, \u0027twig\u0027]` for non-super users. Taxonomy fields are not restricted, so editors can freely set arbitrary taxonomy values.\n\n### XSS Detection Bypass\n\nGrav\u0027s `Security::detectXss()` checks for `dangerous_tags` (e.g., `\u003cscript\u003e`, `\u003ciframe\u003e`), `on_events` (event handlers), and `invalid_protocols` (e.g., `javascript:`). However, the `on_events` regex:\n\n```php\n\u0027on_events\u0027 =\u003e \u0027#(\u003c[^\u003e]+[a-z\\x00-\\x20\"\\\u0027\\/)(?:on[a-z]+)\\s*=[\\s|\\\u0027\"\u0027].*[\\s|\\\u0027\"\u0027]\u003e#iUu\u0027\n```\n\nrequires either quotes around the handler value or a trailing space before `\u003e`. An unquoted handler like `onerror=alert(1)\u003e` (no space before `\u003e`) bypasses this check entirely.\n\nCombined with `\u003c/option\u003e\u003c/select\u003e` to break out of the select context (neither tag is in `dangerous_tags`), the full payload evades all three detection layers and triggers no XSS warning in the admin panel.\n\n### PoC\n\n#### Step 1: Login as Editor\nNavigate to `http://TARGET/admin/` and authenticate with editor credentials.\n\n#### Step 2: Create a Page with Malicious Taxonomy\n- Go to Pages \u2192 Add \u2192 Add Page\n- Title: `XSS via editor`\n- Go to **Options** Tap\n- On Taxonomies, Add tag:\n```\n\u003c/option\u003e\u003c/select\u003e\u003cimg src=x onerror=alert(\u0027XSS-via-editor\u0027)\u003e\n```\n\nThis payload:\n- Closes `\u003c/option\u003e\u003c/select\u003e` to break out of the select dropdown context\n- Injects an `\u003cimg\u003e` tag with an unquoted `onerror` handler (bypasses `on_events` regex)\n- Is not in the `dangerous_tags` list (no `\u003cscript\u003e`, `\u003ciframe\u003e`, etc.)\n- Triggers no XSS warning in the admin panel\n\n\u003cimg width=\"1221\" height=\"857\" alt=\"image\" src=\"https://github.com/user-attachments/assets/6223cbb2-f04b-46bd-89ce-828c89ad77ab\" /\u003e\n\n#### Step 3: Trigger the XSS\nWhen any administrator navigates to the page editor of any page (not just the malicious one), the JavaScript executes immediately.\n\n\u003cimg width=\"1224\" height=\"856\" alt=\"image\" src=\"https://github.com/user-attachments/assets/f008b0f2-dedb-4b22-a74a-cdc0d7325cb4\" /\u003e\n\nThe XSS fires because taxonomy tag options are collected globally across all pages and rendered with `|raw` in the select dropdown template. The payload breaks out of the `\u003coption\u003e` context, and the browser renders the `\u003cimg\u003e` tag as a regular DOM element.\n\n### Impact\n\n- Session hijacking: While `HttpOnly` prevents direct cookie theft, the XSS can steal the admin nonce token and perform any admin action via AJAX requests\n- Privilege escalation: An editor can perform admin-only actions (create users, modify system configuration, install plugins) through the hijacked admin session\n- Cross-page impact: A single malicious taxonomy value affects the entire admin panel - every page editor view is compromised\n\n\n---\n\n## Maintainer note \u2014 fix applied (2026-04-24)\n\nFixed across two repos:\n\n1. **grav-plugin-form 9.0.1** (commit [`6bffb4c`](https://github.com/getgrav/grav-plugin-form/commit/6bffb4c)) \u2014 the primary fix. All four `|raw` filters in [`templates/forms/fields/select/select.html.twig`](https://github.com/getgrav/grav-plugin-form/blob/develop/templates/forms/fields/select/select.html.twig) (placeholder, avalue, suboption, item_value) have been removed. Option labels \u2014 including taxonomy values that propagate cross-page through the admin\u0027s shared selection pool \u2014 now go through Twig\u0027s default escaper, so a lower-privileged editor can no longer inject script that runs in an admin\u0027s browser when they open any page editor.\n\n2. **Grav core on the `2.0` branch** (commit [`5a12f9be8`](https://github.com/getgrav/grav/commit/5a12f9be8), ships in **2.0.0-beta.2**) \u2014 closes the detection-bypass half of the report. The `on_events` regex in `Security::detectXss()` is tightened so unquoted handlers like `onerror=alert(1)\u003e` are flagged (see separate GHSA-9695-8fr9-hw5q), and `option`/`select` have been added to default `security.xss_dangerous_tags` so `\u003c/option\u003e\u003c/select\u003e\u2026` tripwires the detector (see separate GHSA-w8cg-7jcj-4vv2).\n\nSites running admin2 on Grav 2.0.0-beta.2 get the 9.0.1 form plugin automatically via its existing dependency graph.\n\n**Files:**\n- [`templates/forms/fields/select/select.html.twig`](https://github.com/getgrav/grav-plugin-form/blob/develop/templates/forms/fields/select/select.html.twig) \u2014 four `|raw` removed.\n- [`system/config/security.yaml`](https://github.com/getgrav/grav/blob/2.0/system/config/security.yaml) \u2014 dangerous-tags list extended.\n- [`system/src/Grav/Common/Security.php`](https://github.com/getgrav/grav/blob/2.0/system/src/Grav/Common/Security.php) \u2014 `on_events` regex tightened.\n- [`tests/unit/Grav/Common/Security/DetectXssTest.php`](https://github.com/getgrav/grav/blob/2.0/tests/unit/Grav/Common/Security/DetectXssTest.php) \u2014 includes the GHSA-c2q3 PoC payload.",
  "id": "GHSA-c2q3-p4jr-c55f",
  "modified": "2026-05-05T21:24:45Z",
  "published": "2026-05-05T21:24:45Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/getgrav/grav/security/advisories/GHSA-c2q3-p4jr-c55f"
    },
    {
      "type": "WEB",
      "url": "https://github.com/getgrav/grav/commit/5a12f9be8314682c8713e569e330f11805d0a663"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/getgrav/grav"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Grav Vulnerable to XSS via Taxonomy Field Values in Admin Panel"
}