Aituglo, a full-time bug hunter, explains the intricacies of two common types of vulnerabilities in bug hunting: account takeover (ATO) and access control flaws. Although both allow unauthorized actions, they differ significantly; ATO involves an attacker gaining full access to a victim's account by exploiting weak authentication methods, while access control vulnerabilities occur post-authentication, allowing unauthorized access to data or functions due to flawed permission checks. The text delves into various techniques to exploit these vulnerabilities, such as weak password reset flows, cross-site scripting (XSS), insecure direct object references (IDOR), and misconfigurations in OAuth, SAML, and SSO. It also highlights the importance of understanding the distinct nature of these vulnerabilities for effective bug reporting and testing, emphasizing that ATOs typically target the authentication stage, whereas access control issues arise from authorization logic flaws. The severity of these vulnerabilities can vary, with both being considered high-severity bugs depending on the context and data exposed. Aituglo encourages bug hunters to evaluate the impact accurately and adapt their testing approaches to identify and exploit these vulnerabilities effectively.