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Citrix ADC/Netscaler - CVE-2019-19781

The Citrix vulnerability (CVE-2019-19781) was first identified in December of 2019.  This vulnerability is a directory traversal attack that can lead to remote code execution.  So far two directory traversals are needed to execute commands.  One is in the URI and the other is with the NSC_USER: field in the HTTP Header.

The directory traversal allows access to the newbm.pl script.  Through this script, commands can be injected into a new XML file pointed at by the NSC_USER field.  After the commands have been successfully written, a simple GET request to the XML file will execute the commands.

Many proof of concept scripts are available as well as scanners to check and see if your system is vulnerable.  As with many vulnerabilities that affect thousands of systems, we are seeing Crypto Miners taking advantage of it first.

IOCs:

Network:

POST Request with /vpn/../vpns/ and newbm.pl
NSC_USER with ../ in the Header
GET request after the above POST with /vpn/../vpns/ and an .xml file
Request to /vpn/../vpns/cfg/smb.conf  (likely a scanner)

File Type: Shell Script

SHA256:
ff3c0cb8d31360699ec56f1b9f11aa86cb69649ac2f747cdd3b7893b04861f75

SHA1:
301c03b4f943757e1e275ffce13029d53c0f4053

MD5:
0e431d0d9e0fc371c163e4de5226c50b

File Type: ELF

SHA256:
20343854b8c348146bf17fe739ce9028a620f93116438291f1b0b89345e18520feccc

SHA1:
fecccb8a7274992fb76426457bb8a8cc76637d46

MD5:
08f76eb3d62d53bff131d2cb0af2773d

Below is a list of affected devices and the dates that Citrix expects to have a patch ready.  There’s also a link to receive a notification once the patch is available.

Affected Devices:

The vulnerability affects all supported product versions and all supported platforms:

  • Citrix ADC and Citrix Gateway version 13.0 all supported builds
  • Citrix ADC and NetScaler Gateway version 12.1 all supported builds
  • Citrix ADC and NetScaler Gateway version 12.0 all supported builds
  • Citrix ADC and NetScaler Gateway version 11.1 all supported builds
  • Citrix NetScaler ADC and NetScaler Gateway version 10.5 all supported builds 

Version

Refresh Build

Expected Release Date

10.5

10.5.70.x

31st January 2020

11.1

11.1.63.x

20th January 2020

12.0

12.0.63.x

20th January 2020

12.1

12.1.55.x

27th January 2020

13.0

13.0.47.x

27th January 2020

Mitigation Steps:
https://support.citrix.com/article/CTX267679

Bulletin Alerts:
https://support.citrix.com/user/alerts