PT0-002 Attacks and Exploits Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

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  Key confusion attack

  Why it's wrong here

  Key confusion attack (also known as algorithm confusion) occurs when an attacker forces the server to verify an RS256-signed token using HMAC-SHA256 with the server's public key as the shared secret. This works because the public key is often publicly available, and the server may not enforce the expected asymmetric algorithm. It is distinct from alg:none because it still requires a signature, whereas alg:none removes signature verification entirely.

• ✓

  Signature bypass using alg:none

  Why this is correct

  Signature bypass using alg:none exploits a JWT header that sets the algorithm to 'none', which indicates to the parser that the token is unsecured and requires no signature. If the server's library does not explicitly reject 'none' tokens, an attacker can craft a valid-looking token with arbitrary claims simply by setting the header to { 'alg': 'none' } and omitting the signature segment. This effectively bypasses authentication and authorization checks because the token is accepted without any cryptographic proof of origin.

• ✗

  Algorithm substitution attack

  Why it's wrong here

  Algorithm substitution attack is a broader brute-force or downgrade technique where the attacker changes the algorithm parameter to a weaker or symmetric one (e.g., swapping RS256 to HS256) to forge a valid signature. While 'alg:none' is technically a form of algorithm manipulation, security literature typically distinguishes it as a specific signature bypass, not an algorithm substitution, because substitution still requires signing with a known key or guessed secret. In contrast, alg:none eliminates the need for any key material altogether.

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  Timing attack

  Why it's wrong here

  Timing attack is a side-channel technique that measures variations in how long a server takes to process requests, such as during password comparison or HMAC verification. It is unrelated to JWT structure or the alg header; it exploits implementation-specific timing differences to leak secrets like HMAC keys. Since the JWT attack described involves modifying the token's alg field to 'none', timing analysis offers no advantage and does not bypass signature checks.

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