Just a week ago, it was revealed that hackers were exploiting a vulnerability to compromise the VPN gateways used by many businesses worldwide.
Vulnerability, officially known as CVE-2019-19781 but unofficially called "Shitrix", was found on the servers Citrix Application Delivery Controller and Citrix Gateway (known as Netscaler ADC and Netscaler Gateway respectively) but so far Citrix has not released another patch.
Well, there is good news and bad news.
First the good news:
Hackers exploit Shitrix bug to gain access to vulnerable servers, clean up known ones malware infections (such as cryptocurrency mining code) for account and implement the recommended Citrix mitigation measures to prevent future exploit exploitation efforts.
Well, that sounds a bit, isn't it?
So here's the bad news:
In short, hackers have locked other hackers out of vulnerable servers - but not themselves.
The FireEye team has compiled the previous payload installed by the hackers, NOTROBIN.
"FireEye believes that hackers are developing NOTROBIN to prevent the exploitation of the vulnerability of CVE-2019-19781, while maintaining backdoor access to compromised NetScaler devices. Mitigation works by deleting the incremental exploit code found within NetScaler standards before it can be used. However, when the hacker provides the hardcoded key during the subsequent exploitation, NOTROBIN does not remove the payload. This allows the hacker to regain access to the vulnerable device later. ”
"In many investigations, FireEye tracked the hackers who developed NOTROBIN with unique keys. For example, we have recovered about 100 keys from different binaries. These look like MD5 hashes, although FireEye failed to retrieve any plain text. The use of complex, unique keys makes it difficult for third parties, such as competing intruders or FireEye, to easily detect NetScaler devices "protected" by NOTROBIN. This hacker follows a strong password policy! ”
NOTROBIN can successfully inoculate vulnerable devices from Shitrix attacks, but can also open these devices in future campaigns for criminal activities at cyberspace. This is not very similar to the behavior of "Robin Hood" to me.
It's always better to defend your systems yourself or have someone you trust do it for you, rather than having an unknown gang of hackers clean up the mess. After all, you can't be sure they won't have subjects Incentives.
Citrix has promised firmware updates for vulnerable systems by the end of the month.