CVE-2026-40353: Wger Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-6f54-qjvm-wwq3",
  "modified" : "2026-04-24T20:50:44Z",
  "published" : "2026-04-16T01:37:21Z",
  "aliases" : [ "CVE-2026-40353" ],
  "summary" : "wger has Stored XSS via Unescaped License Attribution Fields",
  "details" : "# Stored XSS via Unescaped License Attribution Fields\n\n## Summary\n\nThe `AbstractLicenseModel.attribution_link` property in `wger/utils/models.py` constructs HTML strings by directly interpolating user-controlled fields (`license_author`, `license_title`, `license_object_url`, `license_author_url`, `license_derivative_source_url`) without any escaping. The resulting HTML is rendered in the ingredient view template using Django's `|safe` filter, which disables auto-escaping. An authenticated user can create an ingredient with a malicious `license_author` value containing JavaScript, which executes when any user (including unauthenticated visitors) views the ingredient page.\n\n## Severity\n\n**High** (CVSS 3.1: ~7.6)\n\n- Low-privilege attacker (any authenticated non-temporary user)\n- Stored XSS — persists in database\n- Triggers on a public page (no authentication needed to view)\n- Can steal session cookies, perform actions as other users, redirect to phishing\n\n## CWE\n\nCWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')\n\n## Affected Components\n\n### Vulnerable Property\n**File:** `wger/utils/models.py:88-110`\n\n```python\n@property\ndef attribution_link(self):\n    out = ''\n    if self.license_object_url:\n        out += f'<a href=\"{self.license_object_url}\">{self.license_title}</a>'\n    else:\n        out += self.license_title  # NO ESCAPING\n    out += ' by '\n    if self.license_author_url:\n        out += f'<a href=\"{self.license_author_url}\">{self.license_author}</a>'\n    else:\n        out += self.license_author  # NO ESCAPING\n    out += f' is licensed under <a href=\"{self.license.url}\">{self.license.short_name}</a>'\n    if self.license_derivative_source_url:\n        out += (\n            f'/ A derivative work from <a href=\"{self.license_derivative_source_url}\">the '\n            f'original work</a>'\n        )\n    return out\n```\n\n### Unsafe Template Rendering\n**File:** `wger/nutrition/templates/ingredient/view.html`\n\n- **Line 171:** `{{ ingredient.attribution_link|safe }}`\n- **Line 226:** `{{ image.attribution_link|safe }}`\n\n### Writable Entry Point\n**File:** `wger/nutrition/views/ingredient.py:154-175`\n\n```python\nclass IngredientCreateView(WgerFormMixin, CreateView):\n    model = Ingredient\n    form_class = IngredientForm  # includes license_author field\n```\n\n**URL:** `login_required(ingredient.IngredientCreateView.as_view())` — any authenticated non-temporary user.\n\n**Form fields (from `wger/nutrition/forms.py:295-313`):** includes `license_author` (TextField, max_length=3500) — no sanitization.\n\n### Models Affected\n\n6 models inherit from `AbstractLicenseModel`:\n- `Exercise`, `ExerciseImage`, `ExerciseVideo`, `Translation` (exercises module)\n- `Ingredient`, `Image` (nutrition module)\n\nOnly the **Ingredient** and nutrition **Image** models' attribution links are currently rendered with `|safe` in templates.\n\n## Root Cause\n\n1. `attribution_link` constructs raw HTML by string interpolation of user-controlled fields without calling `django.utils.html.escape()` or `django.utils.html.format_html()`\n2. The template renders the result with `|safe`, bypassing Django's auto-escaping\n3. The `license_author` field in `IngredientForm` has no input sanitization\n4. The `set_author()` method only sets a default value if the field is empty — it does not sanitize user-provided values\n\n## Reproduction Steps (Verified)\n\n### Prerequisites\n- A wger instance with user registration enabled (default)\n- An authenticated user account (non-temporary)\n\n### Steps\n\n1. **Register/login** to a wger instance\n\n2. **Create a malicious ingredient** via the web form at `/en/nutrition/ingredient/add/`:\n   - Set `Name` to any valid name (e.g., \"XSS Form Verified\")\n   - Set `Energy` to `125`, `Protein` to `10`, `Carbohydrates` to `10`, `Fat` to `5` (energy must approximately match macros)\n   - Set `Author(s)` (license_author) to:\n     ```\n     <img src=x onerror=\"alert(document.cookie)\">\n     ```\n   - Submit the form — **the form validates and saves successfully with no sanitization**\n\n3. **View the ingredient page** (public URL, no auth needed):\n   - Navigate to the newly created ingredient's detail page\n   - The XSS payload executes in the browser\n\n### Verified PoC Output\n\nThe rendered HTML in the ingredient detail page (line 171 of `ingredient/view.html`) contains:\n\n```html\n<small>\n     by <img src=x onerror=alert(1)> is licensed under <a href=\"https://creativecommons.org/licenses/by-sa/3.0/deed.en\">CC-BY-SA 3</a>\n</small>\n```\n\nThe `<img>` tag with `onerror` handler is injected directly into the page DOM and executes JavaScript when the browser attempts to load the non-existent image.\n\n### Alternative API Path (ExerciseImage)\n\nFor users who are \"trustworthy\" (account >3 weeks old + verified email):\n\n```bash\n# Upload exercise image with XSS in license_author\ncurl -X POST https://wger.example.com/api/v2/exerciseimage/ \\\n  -H \"Authorization: Token <token>\" \\\n  -F \"exercise=1\" \\\n  -F \"image=@photo.jpg\" \\\n  -F 'license_author=<img src=x onerror=\"alert(document.cookie)\">' \\\n  -F \"license=2\"\n```\n\nNote: ExerciseImage's `attribution_link` is not currently rendered with `|safe` in exercise templates, but the data is stored with XSS payloads and would execute if any template renders it with `|safe` in the future. The API serializer also returns the unescaped `attribution_link` data, which could cause XSS in API consumers (mobile apps, SPAs).\n\n## Impact\n\n- **Session hijacking**: Steal admin session cookies to gain full control\n- **Account takeover**: Modify other users' passwords or email addresses\n- **Data theft**: Access other users' workout plans, nutrition data, and personal measurements\n- **Worm-like propagation**: Malicious ingredient could inject XSS that creates more malicious ingredients\n- **Phishing**: Redirect users to fake login pages\n\n## Suggested Fix\n\nReplace the `attribution_link` property with properly escaped HTML using Django's `format_html()`:\n\n```python\nfrom django.utils.html import format_html, escape\n\n@property\ndef attribution_link(self):\n    parts = []\n\n    if self.license_object_url:\n        parts.append(format_html('<a href=\"{}\">{}</a>', self.license_object_url, self.license_title))\n    else:\n        parts.append(escape(self.license_title))\n\n    parts.append(' by ')\n\n    if self.license_author_url:\n        parts.append(format_html('<a href=\"{}\">{}</a>', self.license_author_url, self.license_author))\n    else:\n        parts.append(escape(self.license_author))\n\n    parts.append(format_html(\n        ' is licensed under <a href=\"{}\">{}</a>',\n        self.license.url, self.license.short_name\n    ))\n\n    if self.license_derivative_source_url:\n        parts.append(format_html(\n            '/ A derivative work from <a href=\"{}\">the original work</a>',\n            self.license_derivative_source_url\n        ))\n\n    return mark_safe(''.join(str(p) for p in parts))\n```\n\nAlternatively, remove the `|safe` filter from the templates and escape in the property, though this would break the anchor tags.\n\n## References\n\n- [Django Security: Cross Site Scripting (XSS) protection](https://docs.djangoproject.com/en/5.0/topics/security/#cross-site-scripting-xss-protection)\n- [Django `format_html()` documentation](https://docs.djangoproject.com/en/5.0/ref/utils/#django.utils.html.format_html)\n- [OWASP: Stored Cross-Site Scripting](https://owasp.org/www-community/attacks/xss/#stored-xss-attacks)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "wger"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "2.4"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/wger-project/wger/security/advisories/GHSA-6f54-qjvm-wwq3"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-40353"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/wger-project/wger"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/wger-project/wger/releases/tag/2.5"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-16T01:37:21Z",
    "nvd_published_at" : "2026-04-17T22:16:33Z"
  }
}