CompTIA PenTest+ (PT0-003)Attacks and ExploitsHard
A tester attempting to compromise a WPA2-PSK wireless network notices the target access point has WPS enabled. The tester uses the reaver tool to systematically try PIN combinations against the AP's WPS interface. What is the primary weakness in the WPS protocol that this attack exploits?
- AWPS uses the same encryption key for all connected clients
- BThe 8-digit WPS PIN is validated in two separate halves, reducing the effective keyspace
- CWPS transmits the passphrase in cleartext during association
- DWPS PINs are stored unencrypted in the access point's firmware
Show answer & explanationAnswer & explanation
Correct answer: B. The 8-digit WPS PIN is validated in two separate halves, reducing the effective keyspace
WPS validates the 8-digit PIN in two halves (the first 4 digits and the last 3 digits, since the 8th digit is a checksum), and the AP confirms each half separately, drastically reducing the brute-force keyspace from 10^8 to roughly 11,000 combinations, which is the core flaw tools like reaver exploit.
Why the other options are wrong
- A. WPS does not use a shared encryption key across clients; this is not the vulnerability exploited.
- C. WPS does not transmit the WPA2 passphrase in cleartext; it uses a PIN exchange protocol, though the flaw lies elsewhere.
- D. WPS PIN storage in firmware is not the exploited weakness; the online brute-force flaw is in the validation process.
WPS PIN Brute-Force Vulnerability
A design flaw in WPS where the 8-digit PIN is verified in two separate halves, allowing attackers like reaver to brute-force the PIN in roughly 11,000 attempts instead of 100 million.
- 8th PIN digit is a checksum, leaving 7 unknown digits
- AP validates first 4 digits and last 3 digits separately
- Reduces brute-force keyspace from 10^8 to about 11,000 combinations
Memory trick: Split the PIN in half and the lock cracks twice as easy.