Linux auto idle logout & vlock possible security problem

From: Czako Krisztian (slapicat_private)
Date: Fri May 29 1998 - 02:29:38 PDT

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There's a possible security problem using auto idle logout programs and vt
lockers.
Try the following:
get the pid of your shell,
(sleep 10s ; kill -HUP <pid-of-your-shell) &
vlock -a

after vlock -a, you can't change the virtual console on a Linux terminal.
But if you log in, start vlock -a, enter your password you can change
vt...

The same happens when an auto idle logout program logs you off. The vlock
(maybe lockvt also)  program doesn't terminate itself after a SIGHUP,
which is ok, but after this, anyone can log in, start vlock -a, enters
his/her password, and get full access to the console.

Possible solutions:
- don't use vlock/lockvt
- don't use auto idle logout program
- as root, never leave your terminal. log off.
if you want to leave, use screen, detach it and log out.

Regards,
Slapic

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