help naming a vulnerability

tedjames

URL: https://www.bedrock.com/accounts/aspx?user=fredflintstone

Essentially, I'm logged in as fredflintstone and can view his account info. Suppose I know the name of another user and modify the URL: https://www.bedrock.com/accounts/aspx?user=joerockhead

Now I can see joerockhead's account info. Moreover, I can modify  joerockhead's info and even delete it.

What would you call that vulnerability?

Edit: I know this is bad form. Just trying to learn.

iBrokeIT

For web vulnerabilities start with the OWASP Top 10.

"A2:2017-Broken Authentication: Application functions related to authentication and session management are often implemented incorrectly, allowing attackers to compromise passwords, keys, or session tokens, or to exploit other implementation flaws to assume other users’ identities temporarily or permanently. "

https://www.owasp.org/images/7/72/OWASP_Top_10-2017_%28en%29.pdf.pdf