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Directory Traversal in Cisco Expressway Gateway

RedTeam Pentesting discovered a directory traversal vulnerability in Cisco Expressway which enables access to administrative web interfaces. 


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:
Vendor Status: fixed version released
Vendor ID: Cisco Bug ID CSCvo47769
Advisory URL:
Advisory Status: published
CVE: CVE-2019-1854


"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:

------------------------------------------------------------------------$(echo -n|base64)/test123

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

------------------------------------------------------------------------$(echo -n|base64)/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:


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:


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



Prevent access to the Cisco Expressway Gateway by untrusted parties. 


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.


2019-02-01 Vulnerability identified
2019-02-20 Customer approved disclosure to vendor
2019-02-21 Vendor notified
2019-02-21 Receipt of advisory acknowledged by vendor
2019-04-16 Vendor announces public disclosure for May 1st to RedTeam Pentesting
2019-05-01 Vendor publishes advisory
2019-05-16 Customer approves release of this advisory
2019-05-17 Advisory released


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