GHSA-6f54-qjvm-wwq3 wger has Stored XSS via Unescaped License Attribution Fields

• PyPI wger: <= 2.4 (no fix yet)

Stored XSS via Unescaped License Attribution Fields Summary The `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. Severity High (CVSS 3.1: ~7.6) • Low-privilege attacker (any authenticated non-temporary user) • Stored XSS — persists in database • Triggers on a public page (no authentication needed to view) • Can steal session cookies, perform actions as other users, redirect to phishing CWE CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') Affected Components Vulnerable Property File: `wger/utils/models.py:88-110` ```python @property def attribution_link(self): out = '' if self.license_object_url: out += f'{self.license_title}' else: out += self.license_title # NO ESCAPING out += ' by ' if self.license_author_url: out += f'{self.license_author}' else: out += self.license_author # NO ESCAPING out += f' is licensed under {self.license.short_name}' if self.license_derivative_source_url: out += ( f'/ A derivative work from the ' f'original work' ) return out ``` Unsafe Template Rendering File: `wger/nutrition/templates/ingredient/view.html` • Line 171: `{{ ingredient.attribution_link|safe }}` • Line 226: `{{ image.attribution_link|safe }}` Writable Entry Point File: `wger/nutrition/views/ingredient.py:154-175` ```python class IngredientCreateView(WgerFormMixin, CreateView): model = Ingredient form_class = IngredientForm # includes license_author field ``` URL: `login_required(ingredient.IngredientCreateView.as_view())` — any authenticated non-temporary user. Form fields (from `wger/nutrition/forms.py:295-313`): includes `license_author` (TextField, max_length=3500) — no sanitization. Models Affected 6 models inherit from `AbstractLicenseModel`: • `Exercise`, `ExerciseImage`, `ExerciseVideo`, `Translation` (exercises module) • `Ingredient`, `Image` (nutrition module) Only the Ingredient and nutrition Image models' attribution links are currently rendered with `|safe` in templates. Root Cause 1. `attribution_link` constructs raw HTML by string interpolation of user-controlled fields without calling `django.utils.html.escape()` or `django.utils.html.format_html()` 2. The template renders the result with `|safe`, bypassing Django's auto-escaping 3. The `license_author` field in `IngredientForm` has no input sanitization 4. The `set_author()` method only sets a default value if the field is empty — it does not sanitize user-provided values Reproduction Steps (Verified) Prerequisites • A wger instance with user registration enabled (default) • An authenticated user account (non-temporary) Steps 1. Register/login to a wger instance 2. Create a malicious ingredient via the web form at `/en/nutrition/ingredient/add/`: • Set `Name` to any valid name (e.g., "XSS Form Verified") • Set `Energy` to `125`, `Protein` to `10`, `Carbohydrates` to `10`, `Fat` to `5` (energy must approximately match macros) • Set `Author(s)` (license_author) to: ``` ``` • Submit the form — the form validates and saves successfully with no sanitization 3. View the ingredient page (public URL, no auth needed): • Navigate to the newly created ingredient's detail page • The XSS payload executes in the browser Verified PoC Output The rendered HTML in the ingredient detail page (line 171 of `ingredient/view.html`) contains: ```html by is licensed under CC-BY-SA 3 ``` The `` tag with `onerror` handler is injected directly into the page DOM and executes JavaScript when the browser attempts to load the non-existent image. Alternative API Path (ExerciseImage) For users who are "trustworthy" (account >3 weeks old + verified email): ```bash Upload exercise image with XSS in license_author curl -X POST https://wger.example.com/api/v2/exerciseimage/ \ -H "Authorization: Token " \ -F "exercise=1" \ -F "[email protected]" \ -F 'license_author=' \ -F "license=2" ``` Note: 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). Impact • Session hijacking: Steal admin session cookies to gain full control • Account takeover: Modify other users' passwords or email addresses • Data theft: Access other users' workout plans, nutrition data, and personal measurements • Worm-like propagation: Malicious ingredient could inject XSS that creates more malicious ingredients • Phishing: Redirect users to fake login pages Suggested Fix Replace the `attribution_link` property with properly escaped HTML using Django's `format_html()`: ```python from django.utils.html import format_html, escape @property def attribution_link(self): parts = [] if self.license_object_url: parts.append(format_html('{}', self.license_object_url, self.license_title)) else: parts.append(escape(self.license_title)) parts.append(' by ') if self.license_author_url: parts.append(format_html('{}', self.license_author_url, self.license_author)) else: parts.append(escape(self.license_author)) parts.append(format_html( ' is licensed under {}', self.license.url, self.license.short_name )) if self.license_derivative_source_url: parts.append(format_html( '/ A derivative work from the original work', self.license_derivative_source_url )) return mark_safe(''.join(str(p) for p in parts)) ``` Alternatively, remove the `|safe` filter from the templates and escape in the property, though this would break the anchor tags. References • Django Security: Cross Site Scripting (XSS) protection • Django `format_html()` documentation • OWASP: Stored Cross-Site Scripting