The issue is being tracked as CVE-2019-19781. If it is left unpatched, it puts companies using either product at risk of phishing attacks, malware, cryptojacking attacks ,and DDoS attacks. That is to name just a few.
According to the researchers, the vulnerability impacts all of the company's enterprise products, including:
Positive Technologies reported the issue to Citrix earlier in December 2019). The company responded quickly and has already issued a patch. The company urges all users of the software mentioned above to apply the patch immediately, because the issue "could allow an unauthenticated attacker to perform arbitrary code execution."
Citrix also recommends making configuration changes in the stand-alone system and running commands from the command line interface. That is, according to a recent blog post on the company's website.
Unfortunately, this vulnerability has been lurking in the shadows since at least 2014, which means that hackers have had plenty of time to exploit the vulnerability. If you're unable to patch your software in the near future, it's important to look for any existing exploitations that may already be compromising your system.
This is a serious, globe-spanning threat. Patching it to keep away from danger should be given highest priority. Kudos to Citrix for their rapid response, but given how long this vulnerability has been waiting to be discovered, the fear that there may be others is there. Stay vigilant and apply the patch as soon as you're able.