full-disclosure - [FD] macOS High Sierra 10.13.1 insecure cron system

Open Source and information security mailing list archives

Message-ID: <9EE49F0E-A889-459F-9F5B-1ABC6E4AB817@rkw.io>
Date: Wed, 06 Dec 2017 08:32:48 +0000
From: "Mark Wadham" <fd@....io>
To: fulldisclosure@...lists.org
Subject: [FD] macOS High Sierra 10.13.1 insecure cron system

Recently I was working on an security issue in some other software that 
has yet
to be disclosed which created a rather interesting condition. As a 
non-root
user I was able to write to any file on the system that was not 
SIP-protected
but the resulting file would not be root-owned, even if it previously 
was.

This presented an interesting challenge for privilege escalation - how 
would you
exploit this to obtain root access? The obvious first attempt was the 
sudoers
file but sudo is smart enough not to process it if the file isn't 
root-owned so
that didn't work.

I then discovered (after a tip from a friend - thanks pndc!) that the 
cron
system in macOS does not care who the crontab files are owned by. 
Getting root
was a simple case of creating a crontab file at:

/var/at/tabs/root

with a 60-second cron line, eg:

* * * * * chown root:wheel /tmp/payload && chmod 4755 /tmp/payload

and then waiting for it to execute. It's not clear if this is a 
macOS-specific
issue or a hangover from the BSD-inherited cron system, I suspect the 
latter.

The issue has been reported to Apple so hopefully they will fix it.

Ref: 
https://m4.rkw.io/blog/macos-high-sierra-10131-insecure-cron-system.html

_______________________________________________
Sent through the Full Disclosure mailing list
https://nmap.org/mailman/listinfo/fulldisclosure
Web Archives & RSS: http://seclists.org/fulldisclosure/

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives