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computer vulnerability announce CVE-2017-3839

Cisco Secure Access Control System: external XML entity injection

Synthesis of the vulnerability

An authenticated attacker can transmit malicious XML data to Cisco Secure Access Control System, in order to read a file, scan sites, or trigger a denial of service.
Impacted products: Secure ACS.
Severity: 2/4.
Creation date: 16/02/2017.
Revision date: 17/02/2017.
Identifiers: CERTFR-2017-AVI-052, cisco-sa-20170215-acs1, CVE-2017-3839, VIGILANCE-VUL-21867.

Description of the vulnerability

XML data can contain external entities (DTD):
  <!ENTITY name SYSTEM "file">
  <!ENTITY name SYSTEM "http://server/file">
A program which reads these XML data can replace these entities by data coming from the indicated file. When the program uses XML data coming from an untrusted source, this behavior leads to:
 - content disclosure from files of the server
 - private web site scan
 - a denial of service by opening a blocking file
This feature must be disabled to process XML data coming from an untrusted source.

However, the Cisco Secure Access Control System parser allows external entities.

An authenticated attacker can therefore transmit malicious XML data to Cisco Secure Access Control System, in order to read a file, scan sites, or trigger a denial of service.
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