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.

• ✗

  Weak secret brute-force

  Why it's wrong here

  Weak secret brute-force is incorrect because it targets JWT / HS256 tokens where the server verifies a token's HMAC-SHA256 signature using a symmetric key that is weak or guessable. An attacker would need to capture a valid signed token and then brute-force the secret to forge new tokens. In contrast, the alg:none attack exploits servers that accept a JWT with the algorithm header set to "none" and no signature at all, so no secret material is involved in the bypass.

• ✗

  Kid injection

  Why it's wrong here

  Kid injection is not the correct answer because it manipulates the JWT header's "kid" (key ID) parameter to reference an attacker-controlled file or value, tricking the server into using that malicious key for signature verification. This attack still requires the server to verify a signature, just against an attacker-chosen key. The alg:none attack, however, completely bypasses signature verification by declaring that no algorithm is used, so the token is accepted without any cryptographic check.

• ✓

  Algorithm confusion (alg:none)

  Why this is correct

  Algorithm confusion (alg:none) is correct because it exploits a JWT library's failure to enforce that the algorithm specified in the token's header matches a secure, expected algorithm. By setting "alg" to "none", the attacker removes the signature entirely and submits a token with only the header and payload; vulnerable servers will trust the token as if it were signed. This attack is particularly successful when the server does not explicitly block the "none" algorithm or fails to validate the token's integrity when no signature is present.

• ✗

  Key confusion

  Why it's wrong here

  Key confusion (also called algorithm substitution) is incorrect here because it mixes HMAC and asymmetric algorithms: an attacker tricks the server into treating an RSA public key as an HMAC secret, then signs a forged token with that public key. This requires the server to support both RS256 and HS256 and to use the public key as the symmetric secret. The alg:none attack is fundamentally different—it demands no signature at all, whereas key confusion still involves producing a valid HMAC signature.

Go deeper

Related to this question