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Many web applications use invite links in the format:
`https://redacted[.]com/invite?token=INV123`
If the token is short, predictable, and not tied to the user’s identity, it becomes vulnerable to enumeration attacks. Attackers can brute-force nearby tokens (INV124, INV125, etc.) to gain unauthorized access to other users’ invites, potentially joining restricted teams or workspaces.
You Should Know:
1. Tools for Token Enumeration
– `ffuf` (Fast Web Fuzzer) – A popular tool for brute-forcing tokens:
ffuf -w /path/to/wordlist.txt -u "https://target.com/invite?token=FUZZ" -fs 0
– Burp Suite Intruder – Useful for systematic token testing:
– Capture the invite request in Burp.
– Send it to Intruder.
– Use a numeric payload (e.g., 100-999) to test sequential tokens.
2. Common Vulnerable Patterns
- Short, Incremental Tokens (e.g.,
INV100,INV101) - Time-Based Tokens (e.g.,
20240504_INV) - Predictable Hashes (e.g., MD5 of user emails)
3. Mitigation Techniques (For Developers)
- Use UUIDs instead of short tokens:
import uuid invite_token = str(uuid.uuid4())
- Bind tokens to user sessions/IPs to prevent misuse.
- Implement short expiration times (e.g., 24 hours).
4. Defensive Checks (For Bug Hunters)
- Verify if the token is bound to the user’s email/session.
- Check if the token expires after first use.
- Test if rate limiting prevents brute-force attacks.
What Undercode Say:
Invite token enumeration is a classic Insecure Direct Object Reference (IDOR) issue. Many platforms overlook token randomness, leading to unauthorized access. Bug hunters should automate token testing with `ffuf` or Burp, while developers must enforce strict token policies.
Expected Output:
A successful token enumeration attack could lead to:
- Unauthorized team access (Slack, Discord, private forums).
- Account takeovers if tokens reset passwords.
- Data leaks from shared workspace resources.
Prediction:
As more apps adopt invite-based onboarding, token enumeration flaws will remain prevalent. Future mitigations may include JWT-based invites or biometric verification to prevent abuse.
For further reading, check:
References:
Reported By: Krishna221619 Bugbountytips – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
