Most hunters scroll past cache-related behavior, thinking:

"This is CDN stuff… not my problem."

"That assumption has paid attackers thousands of dollars."

This post dives into Web Cache Deception — a vulnerability that doesn't exploit your code, but how your application is interpreted by caching layers.

And when it hits, it leaks authenticated user data to the public.

🧠 What Is Web Cache Deception (In Plain English)

Web Cache Deception happens when:

-> A user is logged in

-> They request a dynamic, authenticated page

-> The request looks like a static file

-> A cache (CDN / reverse proxy) stores it

-> Anyone can later access that cached response without authentication

The application thinks:

"User is authenticated → serve private data"

The cache thinks:

"This is a static file → store and reuse"

That mismatch is the bug.

🎯 Why This Bug Is Dangerous (And Pays Well)

This bug often leads to:

-> Profile data leakage

-> Email addresses, phone numbers

-> Account settings

-> API responses

-> Sometimes tokens or internal IDs

And the scariest part?

👉 No victim interaction needed after caching. 👉 One request can expose thousands of users.

That's why this is often rated P1.

📹 Real Exploitation Flow (PoC Mindset)

No brute force. No XSS. No IDOR.

"Just misinterpreted intent."

🧪 How to Find Web Cache Deception (Step-by-Step)

Step 1: Identify Authenticated Endpoints

Login and list pages like:

• /account
• /profile
• /settings
• /dashboard
• /api/user
• /me

If it returns user-specific data, it's a candidate.

Step 2: Append Fake Static Extensions

Try appending extensions that CDNs love to cache:

.css
.js
.jpg
.png
.svg
.ico
.json

Examples:

/account/profile.css
/settings.js
/api/user.json
/dashboard.png

⚠️ Important: Do this while logged in, with cookies intact.

Step 3: Check Cache Headers

Look for headers like:

X-Cache: HIT
X-Cache-Status: HIT
CF-Cache-Status: HIT
Age: 120

If you see HIT, the response is cached.

Step 4: Test Without Authentication

Now:

-> Open incognito

-> Or use curl without cookies

-> Request the same URL

curl https://target.com/account/profile.css

If you still get user data → 💥 vulnerability confirmed.

🧰 Tools You'll Actually Use

🔧 Primary Tools

-> Burp Suite

-> Repeater (manual testing)

-> Proxy (header inspection)

-> curl

-> Browser Incognito Mode

No fancy automation needed.

🧪 Real Payloads That Work

Save these — they work surprisingly often:

/profile.css
/account/settings.jpg
/dashboard.js
/api/me.json
/user/info.png

💡 Tip: .css and .jpg have the highest success rate.

🚩 Advanced Detection Tricks (Pro Level)

1️⃣ Cache Bypass Comparison

Request twice:

/profile
/profile.css

If behavior changes → investigate deeper.

2️⃣ User-to-User Leakage Test

-> Login as User A

-> Cache the page

-> Login as User B

-> Access cached URL

If User B sees User A data → critical impact.

3️⃣ Time-Based Cache Check

Look at:

Age: 300

That means the data has been cached for 5 minutes already.

🧨 Chaining This Bug (How It Becomes P1)

Web Cache Deception becomes lethal when combined with:

-> IDOR → leak arbitrary users

-> API endpoints → structured JSON leaks

-> Profile images / documents

-> OAuth user info endpoints

This is how:

"Low complexity bug" → High business impact

📝 How to Report This (Report-Ready Language)

Title

Web Cache Deception Allows Public Access to Authenticated User Data

Impact

An unauthenticated attacker can retrieve sensitive user-specific information by accessing a cached version of an authenticated endpoint. This may lead to large-scale exposure of user data without any interaction from the victim.

Why This Matters

-> Affects all users behind CDN

-> Breaks authentication guarantees

-> Violates privacy expectations

🧠 Why Most Hunters Miss This Bug

Because:

-> It's not in OWASP Top 10

-> Scanners don't flag it

-> It doesn't "look like a bug"

-> It requires understanding how systems interact

But companies care deeply about it.

🚀 What You Should Do After Reading This

Next time you:

-> See a CDN

-> See authenticated pages

-> See unusual caching headers

👉 Don't ignore it. 👉 Test it.

This one bug alone has earned researchers consistent P1s.

🐾 Coming Next in This Series

In the next post, I'll break down:

👉 OAuth Misbinding — the bug that silently logs victims into attacker accounts 👉 With real flows, payloads, and PoC logic

☕Support the Work (If This Helped You)

If this write-up helped you understand Web Cache Deception better — or saved you hours of trial and error — you can support my work here:

👉 Buy Me a Coffee: Abhijeet Kumawat❤️

Your support helps me keep publishing deep, practical bug bounty content with real attack flows, payloads, and reporting insights — not surface-level theory.

_ No pressure. Just appreciation❤️