Because some people like lists, here is a list of the top 10 recommended, language-neutral, secure coding practices (adopted from https://www.securecoding.cert.org/confluence/display/seccode/Top+10+Secure+Coding+Practices).
1. Validate input. As mentioned in my first security blog post, validating input can eliminate the vast majority of software vulnerabilities. External data sources you are using, e.g. pulling from databases, using APIs, etc., have the capability of having malformed objects or “inappropriate” syntax designed to break your system.
2. Use compiler warnings. When using compiled code (as opposed to interpreted code like Python), ensure the compiler is set to generate the highest warning levels and don’t ignore the warnings when compiling. By eliminating the warnings, you are ensuring that security vulnerabilities don’t exist in your code, to the best of your ability.
3. Design based on security policies. Develop your software architecture and develop the code base around established security policies. For example, design your system to have independent subsystems that can communicate with each other; each subsystem has a different privilege level so the highest privilege isn’t being used all the time. A similar example of this is that Windows XP and older versions defaulted to giving each user administrator privileges, making it easy for malware to execute.
4. KISS (Keep It Simple, Stupid). The more complex you design something, the more likely errors and vulnerabilities will creep in. If your programming language allows for subroutines, subprocesses, modules, etc., then use them to break up the program into smaller parts. It is easier to troubleshoot and debug these smaller sections than try to work with a monolithic program.
5. Deny by default. When setting permissions, assume access is denied until proven otherwise. Also, ensure that conditions are identified for when access is permitted.
6. Use the concept of least privilege. Much like #5 above, every process should be executed with the minimum privileges required to complete the job. If a process has to have a higher level of access, that access should be removed as soon as possible. This removes many of the avenues malicious attacks can use for privilege escalation.
7. Sanitize data transfers. When passing data to other subsystems, such as databases, other programs, command shells, etc., sanitize the data first. Unused functionality within these other systems can be attacked through a number of vectors. Sanitizing your data can remove some of these vectors, as your program knows the context of the data transfer; the called system doesn’t know anything about the transfer and will accept whatever it is given.
8. Practice defense in depth. Use multiple defensive measures so attacks have to circumvent a variety of countermeasures in order to run. For example, use a sandbox environment (like a virtual machine) when testing unknown code to minimize the risk of damaging your system.
9. Make use of quality assurance testing. Good QA can identify and remove vulnerabilities. When possible, have someone else look at your code; the programmer may become so used to looking at the code that he or she may miss something obvious. Automated tools can quickly find common errors while audits can track frequent problems and provide better education.
10. Create a secure coding standard. Develop and implement a secure standard for programmers, taking into consideration the programming language(s) used and the target platforms.
11. Define security requirements. Identify security requirements early in the development cycle and, whenever changes are made to the development plan, ensure the changes are vetted against the requirements.
12. Use threat modeling. Anticipate possible threats to the software and develop mitigation strategies to address these threats. Identify key assets of the software and system, decompose the application, categorize threats, and then rate the threats.