1) National Vulnerability Database https://nvd.nist.gov/
NVD i.e. National Vulnerability Database is a product of NIST (National Institute of Standards and Technology) Computer Security Division which is sponsored by DHS(Dept. of Homeland Security’s). The NVD is the U.S. government repository of standards based vulnerability management data represented using the Security Content Automation Protocol (SCAP). This data enables automation of vulnerability management, security measurement, and compliance.
The NVD includes databases of security checklist references, security related software flaws, misconfigurations, product names, and impact metrics.
2) Security Tracker https://securitytracker.com/
SecurityTracker is a premier vulnerability and patch notification service which provides 24/7 real tiime vulnerability notification, including customizable alerts and expert analysis and content tailored to your specific product requirements.
3) SecuriTeam http://securiteam.com/
SecuriTeam is a small group within Beyond Security dedicated to bringing you the latest news and utilities in computer security.
4) Secunia http://secunia.com/
The Secunia Research team is comprised of a number of Secunia security specialists, who besides testing, verifying, and validating public vulnerability reports, also conduct their own vulnerability research in various products.
5) HackerStorm http://hackerstorm.co.uk/
HackerStorm helps with vulnerability research and improve the success of your penetration testing.