Some common vulnerabilities and exploits in e-commerce sites are-
- SQL injections
- Price manipulation
- Buffer overflow
- Cross-site scripting
- Remote command execution
- Weak authentication and authorization
Some common weakness and attacks in social networking applications are-
- Cross-Site Request Forgery (CSRF)
- Cross-Site Scripting (XSS)
- Database Injection
- Open Redirector
- Privacy/Authentication
Most of them overlap and are clearly part of the OWASP Top Ten web vulnerabilities.
References-
https://www.symantec.com/connect/articles/common-security-vulnerabilities-e-commerce-systems