Among the previously mentioned proposals, the so-called OWASP Top 10 is by far the most requested among programmers all over the world.
Its main goal is to help developers identify the most critical security risks facing organizations. To help in the task, they publish a periodical bulletin which has been published since they started in 2010. The current, updated version is the 2013 edition, although they're working on a version for 2017, which is not available at the time of writing this.
The top 10 vulnerabilities are presented in the following graphic. It assumes that the ordering is important, the first one being the most used or dangerous (or both, in many cases):
Also, keep in mind that often, an attack can be a compound of different steps, each step using some of these vulnerabilities (this happens in some of the most sophisticated attacks we know of).
In the diagram, OWASP explains a use case in which an actor gets access to a valuable resource and the elements involved in the process. Somehow, the vast majority of the attacks follow this sequence diagram:
As the paper states, the paths used by threat agents can be simple or tremendously complex. Often, they can be very difficult to identify and reproduce. They recommend the following:
"To determine the risk to your organization, you can evaluate the likelihood associated with each threat agent, attack vector, and security weakness and combine it with an estimate of the technical and business impact to your organization. Together, these factors determine the overall risk."
If you remember Chapter 10, Design Patterns, there is a relation to the Threat Model, that is, basically, the same message we mentioned when talking about threats.
So, it seems that there's a consensus about security management and the principles that should be considered along the application's life cycle.
The top 10 list of threats that we are going to cover in this chapter explain the roots of every vulnerability, typical scenarios for attacks, and the recommended prevention measures. We'll review them and look at the ways in which they affect the C# and .NET programmers.
Let's start by quoting these ten definitions and establish them as the starting point of our analysis (there's a free version of the document available at http://www.owasp.org):
- A1 - Injection: Injection flaws, such as SQL, OS, and LDAP injection occur when untrusted data is sent to an interpreter as part of a command or query. The attacker's hostile data can trick the interpreter into executing unintended commands or accessing data without proper authorization.
- A2 - Broken Authentication and Session Management Application: Application functions related to authentication and session management are often not implemented correctly, allowing attackers to compromise passwords, keys, or session tokens, or to exploit other implementation flaws to assume other users' identities.
- A3 - Cross-Site Scripting (XSS): XSS flaws occur whenever an application takes untrusted data and sends it to a web browser without proper validation or escaping. XSS allows attackers to execute scripts in the victim's browser which can hijack user sessions, deface web sites, or redirect the user to malicious sites.
- A4 - Insecure Direct Object References: A direct object reference occurs when a developer exposes a reference to an internal implementation object, such as a file, directory, or database key. Without an access control check or other protection, attackers can manipulate these references to access unauthorized data.
- A5 - Security Misconfiguration: Good security requires having a secure configuration defined and deployed for the application, frameworks, application server, web server, database server, and platform. Secure settings should be defined, implemented, and maintained, as defaults are often insecure. Additionally, software should be kept up to date.
- A6 – Sensitive Data Exposure: Many web applications do not properly protect sensitive data, such as credit cards, tax IDs, and authentication credentials. Attackers may steal or modify such weakly protected data to conduct credit card fraud, identity theft, or other crimes. Sensitive data deserves extra protection such as encryption at rest or in transit, as well as special precautions when exchanged with the browser.
- A7 – Missing Function Level Access Control: Most web applications verify function level access rights before making that functionality visible in the UI. However, applications need to perform the same access control checks on the server when each function is accessed. If requests are not verified, attackers will be able to forge requests in order to access functionality without proper authorization.
- A8 - Cross-Site Request Forgery (CSRF): A CSRF attack forces a logged-on victim's browser to send a forged HTTP request, including the victim's session cookie and any other automatically included authentication information, to a vulnerable web application. This allows the attacker to force the victim's browser to generate requests that the vulnerable application thinks are legitimate requests from the victim.
- A9 - Using Components with Known Vulnerabilities: Components, such as libraries, frameworks, and other software modules, almost always run with full privileges. If a vulnerable component is exploited, such an attack can facilitate serious data loss or server takeover. Applications using components with known vulnerabilities may undermine application defenses and enable a range of possible attacks and impacts.
- A10 – Unvalidated Redirects and Forwards: Web applications frequently redirect and forward users to other pages and websites, and use untrusted data to determine the destination pages. Without proper validation, attackers can redirect victims to phishing or malware sites, or use forwards to access unauthorized pages.
As we can see, there are 10 distinct areas to care about, which we should consider as programmers, although the team in charge of envisioning and planning the application should also keep them in mind from the very beginning of any software project.
So, let's go with the A1 threat, which is the mother of all evil for many programmers: injection in its many flavors.