I. VULNERABILITY
-------------------------
Microsoft Skype for Business External Service Interaction (DNS)
Latest Version

II. CVE REFERENCE
-------------------------
Not Assigned Yet

III. VENDOR
-------------------------
https://www.microsoft.com

IV. TIMELINE
-------------------------
28/11/2019 Vulnerability discovered
03/12/2019 Vendor contacted
04/12/2019 Microsoft replay that “We determined that this behavior is
considered to be by design.”

V. CREDIT
-------------------------
Alphan Yavas from Biznet Bilisim A.S.

VI. DESCRIPTION
-------------------------
Microsoft Skype for Business latest versions affected from external
service interaction(DNS) vulnerability. A remote attacker could force
the vulnerable server to send DNS request to any remote server
attacker wants.

VII. PROOF OF CONCEPT
-------------------------
Affected Component:
Path(inurl): /Dialin/Conference.aspx
Parameter: Username

Login page of Skype for Business affected from external service
interaction (DNS) vulnerability. If username is being sent with
following format victim server will send out DNS queries to xxx
domain.  (xxx is the domain which you want to send request from
server)

username: ssrf.xxx.com\pentest
password: (doesn't matter)

Reference: https://portswigger.net/kb/issues/00300200_external-service-interaction-dns