How to exploit vulnerabilities and their damage potentials are mainly affected by the capability of attackers. The more powerful the attacker, the greater risk of threats and vulnerabilities. Therefore, the security analysis of a web application and choosing risk mitigation countermeasures depend on the ability of the attackers threaten the application. Focusing on SQL injection attacks, this paper is aimed at modeling the attacker’s capability to be further used for appropriate security evaluation and choosing cost-effective security controls. We model the attacker’s capability with the triple ⟨Type, Technique, Entry_Point⟩. The value in each component of the triple is obtained from the payloads through which the attacker tries to exploit the injection vulnerabilities. The Type represents the injection type, including a known set of injection attack types namely, Error_based, Union_based, Boolean_based_Blind and etc. The Technique represents the techniques, which are used by the attacker during the attack, e.g. using Special Character, using UNION, using Complex Query, using Encoding and etc. Finally, the Entry_Point represents the set of known injection entry points including GET/POST method, Http_Variables, Frequenc_based_Primary_Application and etc. This model is used for leveling and comparing the attacker’s capabilities as well as for leveling the security of a web application with respect to the level of the attacker who is able to compromise the web application. The results of the experimental evaluation show that the proposed model can be used to determine the attacker’s capability level. The model can be simply extended to adopt other security vulnerabilities attacks.