How do you remediate Stored Cross-Site Scripting (XSS) and Broken Object Level Authorization (BOLA)?

Remediate stored XSS by applying context‑aware output encoding at the point of rendering and by enforcing a strict Content‑Security‑Policy; fix BOLA by implementing server‑side authorization checks that validate the caller’s rights against the specific object ID. **Remediation checklist** 1. **Input handling** – Reject or sanitize dangerous characters on entry (e.g., use `express-validator` in Node or `django.forms` clean methods). Do not rely on client‑side validation. 2. **Output encoding** – Encode data based on context: ```javascript // Node/Express with npm `xss-filters` const safe = require('xss-filters').inHTMLData(userInput); res.send(``); ``` ```csharp // ASP.NET Core @HtmlEncoder.Default.Encode(userInput) ``` 3. **Content‑Security‑Policy** – Deploy a CSP that disallows `unsafe-inline` and restricts script sources: ```http Content-Security-Policy: default-src 'self'; script-src 'self' https://cdn.example.com; object-src 'none'; ``` 4. **HTTP‑Only & Secure cookies** – Set `HttpOnly; Secure; SameSite=Strict` to mitigate session theft. 5. **BOLA enforcement** – Before any object operation, fetch the object’s owner or ACL and compare it to the authenticated principal: ```python # Django view obj = MyModel.objects.get(pk=obj_id) if obj.owner_id != request.user.id: raise PermissionDenied() ``` Or with OPA: ```rego allow { input.method = "GET" input.path = ["api","orders", order_id] data.authz[subject].orders[order_id] == "read" } ``` 6. **Audit & testing** – Run automated scans (e.g., OWASP ZAP, Burp Suite) and include unit tests that assert `403` on unauthorized object IDs. **Gotcha:** Rendering user‑generated HTML via `innerHTML` or server‑side templating functions that bypass the encoder will re‑introduce XSS even with a CSP in place. Use a safe DOM API (`textContent`) or a sanitization library like DOMPurify.