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Actively exploited vulnerability

Citrix NetScaler SD-WAN Enterprise, CloudBridge Virtual WAN, and XenMobile Server: code execution flaw under attack

CVE-2017-6316 · Citrix Multiple Products Remote Code Execution Vulnerability

Business software9.8 critical

What is affected

Citrix NetScaler SD-WAN Enterprise, CloudBridge Virtual WAN, and XenMobile Server is mostly run by companies, schools and public bodies, not on home computers. You are unlikely to have it yourself, but organisations that hold your data may. Breaches that start with flaws like this one are how personal data ends up leaked.

A vulnerability has been identified in the management interface of Citrix NetScaler SD-WAN Enterprise and Standard Edition and Citrix CloudBridge Virtual WAN Edition that could result in an unauthenticated, remote attacker being able to execute arbitrary code as a root user. This vulnerability also affects XenMobile Server.

CISA's description

What an attacker can do

This is a code execution flaw. It lets an attacker run their own commands or programs on the affected system. In practice that usually means taking it over: installing malware, stealing data or using it to reach other devices on the same network.

How it is reached
Over the internet or network
Access the attacker needs
No account needed
Does the victim have to do something?
No, works without the victim doing anything

What to do

  1. At home: nothing to install. Keep your own devices updated and use a different password for every service, so that a breach at one organisation does not open your other accounts.
  2. If you administer Citrix NetScaler SD-WAN Enterprise, CloudBridge Virtual WAN, and XenMobile Server at work: apply the vendor's fix or mitigation now and review logs for signs of compromise, because the flaw was being exploited before it was listed.
  3. If the product is past its support date and no fix exists, take it off the internet or retire it.

Apply updates per vendor instructions.

Action required by CISA for US federal agencies

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on March 25, 2022, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by April 15, 2022, a deadline that has already passed. That deadline does not bind anyone else, but it shows how seriously the agency rates it.

The EPSS model estimates a 73% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 99.4% of all scored vulnerabilities.

Its CVSS severity score is 9.8 out of 10 (critical), as recorded in the US National Vulnerability Database.

Technical description

Citrix NetScaler SD-WAN devices through v9.1.2.26.561201 allow remote attackers to execute arbitrary shell commands as root via a CGISESSID cookie. On CloudBridge (the former name of NetScaler SD-WAN) devices, the cookie name was CAKEPHP rather than CGISESSID.

NIST National Vulnerability Database
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