FYI: Someone’s scanning for gateways containing those security holes Citrix told you not to worry too much about

VIdeo This week Citrix tried to reassure everyone the 11 security flaws it just patched in its network perimeter products weren’t all that bad. Well, we hope they’re right because someone’s scanning the internet looking for vulnerable installations.

The sweeps could be made by researchers documenting at-risk organizations, or could be miscreants looking for unpatched internet-facing gear to meddle with, or both. You probably don’t want to find out the hard way, so apply fixes as soon as you can.

SANS dean of research Johannes Ullrich today said his honeypot, set up to detect exploitation attempts against bugs in F5’s products, encountered attempts by someone to exploit a couple of the holes Citrix patched in its gear.

From the logs, it appears the connections were made to determine whether or not Ullrich’s machine was vulnerable, which it wasn’t because it wasn’t running the buggy Citrix ADC, Citrix Gateway, or Citrix SD-WAN WANOP software. Perhaps if the honeypot was vulnerable, further exploitation may have been attempted. Ullrich believes the attempts targeted CVE-2020-8195 and CVE-2020-8196, both information disclosure flaws.

The Register understands the probing began shortly after Citrix CISO Fermin Serna said on Tuesday a number of the bugs had “barriers to exploitation” that would make them impractical to target in the wild.

The first exploit that hit the honeypot, said Ullrich, attempted to fetch a file from the gateway, in this case the list of accounts and hashed passwords:

POST /rapi/filedownload?filter=path:%2Fetc%2Fpasswd

The second exploit attempt tried to fetch a PCI DSS compliance document from the server:

POST /pcidss/report?username=nsroot&set=1&type=allprofiles&sid=loginchallengeresponse1requestbody

“The vulnerability isn’t all that ‘bad’. I have to look if the [PCI DSS] report leaks anything specific,” he said. “It could very well be used to identify unpatched devices.”

You can find technical details on the Citrix vulnerabilities here, along with proof-of-concept exploits, by Donny Maasland. This code can upload, create, download, and delete arbitrary files on a vulnerable installation, we’re told.

And below is a video showing how the Cross Site Scripting (XSS) flaw (CVE-2020-8198) in Citrix’s software can be abused to gain control over a gateway: a logged-in administrator has to be tricked into clicking on a booby-trapped link. ®

Youtube Video