A penetration tester conducts a web application assessment and receives the following Set-Cookie upon logging...

The correct answer is C. Session hijacking

The cookie value is only Base64 encoded, not encrypted or cryptographically protected. When decoded, it reveals a username and a numeric value:

Pentestuser:91536

After logging in again, the numeric value changes:

Pentestuser:91944

This strongly suggests the application may be storing a session identifier or authentication token in a predictable or weakly protected format. A penetration tester would most likely test whether the session value can be guessed, reused, modified, or replayed to take over another user’s session. That type of attack is session hijacking.

A is incorrect because a collision attack involves finding two different inputs that produce the same hash value. This scenario does not involve hash collision testing.

B is incorrect because JWT manipulation applies to JSON Web Tokens, which typically have three Base64URL-encoded sections separated by periods, such as header.payload.signature. The cookie shown is not a JWT.

D is incorrect because insecure direct object reference involves manipulating object identifiers, such as account IDs, invoice numbers, or file IDs, to access unauthorized resources. The issue here is related to authentication/session handling, not direct object access.

In PenTest+ terms, this falls under Attacks and Exploits, specifically web application attacks involving weak session management, predictable session tokens, and session hijacking.