Hackers Scanning for Citrix Servers Vulnerable to Remote Code Execution

Researchers spotted active scans targeting Application Delivery Controller and Citrix Gateway to exploit Critical Vulnerability CVE-2019-19781.

This vulnerability can be exploited remotely, successful exploitation allows an unauthenticated attacker to perform arbitrary code execution.

The vulnerability was discovered by Mikhail Klyuchnikov, it may create a serious threat for organizations deployed with Citrix Application Delivery Controller and gateway.

Active Scans Spotted

SANS Technology Institute Dean of Research, Johannes B. Ullrich, spotted active scans through honeypot logs. The good news is that no exploits are being used.

Johannes said that the scans are not sophisticated, as they have some of the errors. He also said that “the attackers were able to create a code execution exploit.”

Multiple requests were spotted started from the basic level to some dangerous requests. The requests don’t trigger the exploit as it’s parts are missing, but they hit the vulnerable URLs.

Another researcher Kevin Beaumont said that active exploitation for the vulnerability is starting up.

According to Citrix advisory the vulnerability affects following product versions 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

Citrix not released any patches, but suggested configuration changes to mitigate the execution vulnerability.

Citrix believed to be used in more than 80,000 companies around the globe, successful exploitation of the vulnerability allows an unauthenticated attacker to access internal company applications.

Citrix strongly urges affected customers to immediately apply the provided mitigation. Customers should then upgrade all of their vulnerable appliances to a fixed version of the appliance firmware when released.

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