su failing with "su: Authentication failure" using correct password

Solution Verified - Updated -

Issue

  • Users cannot escalate to root user using su using valid password.
  • It is possible to login as root user directly but not possible to escalate to root using su.
  • Users cannot use su command to switch user getting "su: Authentication failure".
  • Being root you can use su to switch to another user, but regular users are not able to run su.

RHEL5/6:

[user@localhost ~]$ su
Password:
su:  incorrect password
[user@localhost ~]$ su user2
Password:
su:  incorrect password

RHEL7/8:

[user@localhost ~]$ su
Password:
su: Authentication failure
[user@localhost ~]$ su user2
Password:
su: Authentication failure

Environment

  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 7
  • Red Hat Enterprise Linux 8
  • Red Hat Enterprise Linux 9
  • su

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