[Full-disclosure] screen 4.0.3 local Authentication Bypass

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                       Helith - 0815

Author: Rembrandt
Date: Known since somewhere in &cant_remember
Affected Software: screen <= 4.0.3
Type: Local
Type: Authentication Bypass

Greets go to: Helith and all affiliated People, t3c0, levent, str0ke,
hdm, The EOF-Crew, rrlf, herm1t, Solar Designer, softxor,
Packetstorm, FeFe, kscope, Zarathu, f0rg3, Mr. Joern Alles

Disrespect goes to: A Bank [/]
And others included into this case…

Personal note: I wanna get MY STUFF BACK!
This is the last "diplomatic" attemp made directly.
Contact me if you`re interested into a deescalation.
Nobody is interested into making the things even more complicated
or? So make your choice. And you better hurry…
And this is no blackmailing attemp but others may decide for you
if you don`t do it.
IMPORTENT: Turn your brain "ON" this time.

I didn`t found a Adv. related to this so I decided to write one. :]

screen is vulnerable to a authentication bypass which allows local attackers
to gain system access in case screen was locked with a Password.

It has been tested on OpenBSD 4.1 + screen 4.0.3 on x86.

How to reproduce:

Lock screen using ctrl+x
Choose a Password
Confirm the Password

Screen asks for a Password to unlock the screen.
Just press ctrl+c and it displays "Getpass error".
2 seconds later the screen is unlocked and you`ve access.

Have fun!