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GUIDANCE FOR ADDRESSING CITRIX NETSCALER ADC AND GATEWAY VULNERABILITY
CVE-2023-4966, CITRIX BLEED

Related topics:
Cybersecurity Best Practices


Note: CISA will continue to update this webpage as we have further guidance to
impart.


SUMMARY

CISA and our partners are responding to active, targeted exploitation of a
vulnerability, CVE-2023-4966, affecting Citrix NetScaler ADC and NetScaler
Gateway. The vulnerability is also known as Citrix Bleed. The affected products
contain a buffer overflow vulnerability that allows for sensitive information
disclosure when configured as a Gateway (VPN virtual server, ICA Proxy, CVPN,
RDP Proxy) or AAA virtual server. Customers using Citrix-managed cloud services
or Citrix-managed Adaptive Authentication are not impacted.

Exploitation of this vulnerability could allow for the disclosure of sensitive
information, including session authentication token information that may allow a
threat actor to “hijack” a user’s session[1].


TECHNICAL DETAILS

On Oct. 10, 2023, Citrix released security updates(link is external) to address
CVE-2023-4966 in NetScaler ADC and NetScaler Gateway.

On Oct. 17, Citrix updated its Alert to include “exploits of CVE-2023-4966 on
unmitigated appliances have been observed.”

On Oct. 18, CISA added an entry for CVE-2023-4966 to its Known Exploited
Vulnerabilities (KEV) catalog, which contains detection and mitigation guidance
for observed exploitations of CVE-2023-4966.

On Oct. 23, Citrix released a blog(link is external), providing recommended next
steps and a link to Mandiant’s Oct. 17 guidance for remediating and reducing
risks related to CVE-2023-4966: Remediation for Citrix NetScaler ADC and Gateway
Vulnerability (CVE-2023-4966)(link is external).

CISA urges organizations to update unmitigated appliances to the updated
versions listed below, hunt for any malicious activity, and report any positive
findings to CISA. 

 * NetScaler ADC and NetScaler Gateway 14.1-8.50  and later releases
 * NetScaler ADC and NetScaler Gateway  13.1-49.15  and later releases of 13.1
 * NetScaler ADC and NetScaler Gateway 13.0-92.19 and later releases of 13.0 
 * NetScaler ADC 13.1-FIPS 13.1-37.164 and later releases of 13.1-FIPS 
 * NetScaler ADC 12.1-FIPS 12.1-55.300 and later releases of 12.1-FIPS 
 * NetScaler ADC 12.1-NDcPP 12.1-55.300 and later releases of 12.1-NDcPP
 * Note: NetScaler ADC and NetScaler Gateway version 12.1 is now End-of-Life
   (EOL). Customers are recommended to upgrade their appliances to one of the
   supported versions that address the vulnerabilities.


RESOURCES

This information is provided “as-is” for informational purposes only. CISA does
not endorse any company, product, or service referenced below.


MITIGATION GUIDANCE

 * Citrix Blog: CVE-2023-4966: Critical security update now available for
   NetScaler ADC and NetScaler Gateway(link is external)
 * Citrix Advisory: NetScaler ADC and NetScaler Gateway Security Bulletin for
   CVE-2023-4966(link is external)
 * Citrix NetScaler secure deployment guide: Best practices for NetScaler MPX,
   VPX, and SDX security(link is external).


ADDITIONAL RESOURCES

 * CISA: BOD 23-02: Mitigating the Risk from Internet-Exposed Management
   Interfaces
 * Mandiant:
   * Remediation for Citrix NetScaler ADC and Gateway Vulnerability
     (CVE-2023-4966)(link is external)
   * Investigation of Session Hijacking via Citrix NetScaler ADC and Gateway
     Vulnerability (CVE-2023-4966)(link is external)
 * Assetnote: Citrix Bleed: Leaking Session Tokens with CVE-2023-4966(link is
   external)
 * Palo Alto Networks: Threat Brief: Citrix Bleed CVE-2023-4966(link is
   external)

 

--------------------------------------------------------------------------------

[1]Investigation of Session Hijacking via Citrix NetScaler ADC and Gateway
Vulnerability (CVE-2023-4966) | Mandiant(link is external)

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