Advisory: XML External Entity Expansion in Paessler PRTG Network Monitor Authenticated users who can create new HTTP XML/REST Value sensors in PRTG Network Monitor can read local files on the PRTG host system via XML external entity expansion. Details ======= Product: Paessler PRTG Network Monitor Affected Versions: 14.4.12.3282 Fixed Versions: 16.2.23.3077/3078 Vulnerability Type: XML External Entity Expansion Security Risk: medium Vendor URL: https://www.paessler.com/ Vendor Status: fixed version released Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2015-012 Advisory Status: published CVE: CVE-2015-7743 CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-7743 Introduction ============ "PRTG Network Monitor is the powerful and comprehensive network monitoring solution from Paessler AG. It monitors your network using a whole range of technologies and assures the availability of network components and measures traffic and usage. PRTG saves costs by avoiding outages, optimizing connections, saving time and controlling service level agreements (SLAs)." (from the vendor's website)[1] More Details ============ An attacker with access to a PRTG Network Monitor account with sufficient privileges to create or configure XML/REST sensors can read files stored on the system's local disk. These sensors are intended to query a URL and, depending on the configuration, check whether there is a valid response or read the value of a specific XML node in the document that is returned. This functionality is vulnerable to XML external entity expansion. Proof of Concept ================ In order to exploit this vulnerability an HTTP XML/REST Value sensor has to be set up to access an attacker-controlled URL and to read the value of a specific XML node, for example: https://attacker.example.com/xeee-hosts.xml The XML document "xeee-hosts.xml" contains an external entity that uses the "SYSTEM" keyword to load a local file as the content of the "hosts" entity: <?xml version="1.0"?> <!DOCTYPE root [ <!ENTITY hosts SYSTEM "file://C:WindowsSystem32driversetchosts"> ]> <root>&hosts;</root> Since the XML parser of PRTG Network Monitor evaluates external entities, the XML parser fetches the file "C:WindowsSystem32driversetchosts" from the disk of the local system and inserts its content into the "root" node of the XML document. If the sensor is configured to return the value of that "root" node, the contents of that file are displayed in the web interface of PRTG Network Monitor. This discloses the contents of the file to attackers which otherwise would not be able to read local files. Fix === Update to a version greater or equal to 16.2.23.3077/3078 (see [2]). Security Risk ============= Attackers who can create new HTTP XML/REST sensors in PRTG Network Monitor, are able to use the XML external entity expansion to read files on the local system. Depending on the data stored on the vulnerable system, this vulnerability may pose a high risk. However, as attackers are required to already have valid user credentials for the application, the vulnerability is only rated to have a medium risk potential. Timeline ======== 2015-08-28 Vulnerability identified in PRTG Network Monitor 2015-09-04 Customer approved disclosure of vulnerability 2015-09-04 CVE ID requested 2015-09-24 CVE ID requested again 2015-10-07 CVE ID assigned 2015-10-21 Vendor contacted 2016-04-04 Vendor released fixed version 2016-05-31 Advisory released References ========== [1] https://www.paessler.com [2] https://www.paessler.com/prtg/history/stable RedTeam Pentesting GmbH ======================= RedTeam Pentesting offers individual penetration tests performed by a team of specialised IT-security experts. Hereby, security weaknesses in company networks or products are uncovered and can be fixed immediately. As there are only few experts in this field, RedTeam Pentesting wants to share its knowledge and enhance the public knowledge with research in security-related areas. The results are made available as public security advisories. More information about RedTeam Pentesting can be found at https://www.redteam-pentesting.de. -- RedTeam Pentesting GmbH Tel.: +49 241 510081-0 Dennewartstr. 25-27 Fax : +49 241 510081-99 52068 Aachen https://www.redteam-pentesting.de Germany Registergericht: Aachen HRB 14004 Geschäftsführer: Patrick Hof, Jens Liebchen