Improving Web Application Security: Threats and - CGISecurity

42 Part I: Introduction to Threats and CountermeasuresUser Denies Performing an OperationThe issue of repudiation is concerned with a user denying that he or she performedan action or initiated a transaction. You need defense mechanisms in place to ensurethat all user activity can be tracked and recorded.Countermeasures to help prevent repudiation threats include:● Audit and log activity on the Web server and database server, and on theapplication server as well, if you use one.● Log key events such as transactions and login and logout events.●Do not use shared accounts since the original source cannot be determined.Attackers Exploit an Application Without Leaving a TraceSystem and application-level auditing is required to ensure that suspicious activitydoes not go undetected.Countermeasures to detect suspicious activity include:●●●Log critical application level operations.Use platform-level auditing to audit login and logout events, access to the filesystem, and failed object access attempts.Back up log files and regularly analyze them for signs of suspicious activity.Attackers Cover Their TracksYour log files must be well-protected to ensure that attackers are not able to covertheir tracks.Countermeasures to help prevent attackers from covering their tracks include:● Secure log files by using restricted ACLs.● Relocate system log files away from their default locations.SummaryBy being aware of the typical approach used by attackers as well as their goals, youcan be more effective when applying countermeasures. It also helps to use a goalbasedapproach when considering and identifying threats, and to use the STRIDEmodel to categorize threats based on the goals of the attacker, for example, to spoofidentity, tamper with data, deny service, elevate privileges, and so on. This allowsyou to focus more on the general approaches that should be used for risk mitigation,rather than focusing on the identification of every possible attack, which can be atime-consuming and potentially fruitless exercise.