Citrix's NetScaler ADC and NetScaler Gateway have, once more, been found to have multiple vulnerabilities, tracked as CVE-2023-4966 and CVE-2023-4967

On October 23, 2023, GreyNoise Detection Engineers added tag coverage for CVE-2023-4966, which is an information disclosure vulnerability in NetScaler ADC and NetScaler Gateway. When configured as a gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or as an AAA virtual server, an unauthenticated attacker could exploit the device in order to hijack an existing authenticated session. Depending on the permissions of the account they have hijacked, this could allow the attacker to gain additional access within a target environment and collect other account credentials. 

CVE-2023-4967 is a denial-of-service (DoS) vulnerability that can potentially enable DoS attacks on vulnerable devices. 

Both CVEs were published on October 10, 2023, and the tag for CVE-2023-4966 joins 11 other Citrix-specific tags in the GreyNoise tag corpus.

The GreyNoise Storm⚡Watch webcast/podcast provided extensive coverage of this vulnerability in this week’s episode.

Widespread Attacks

As of this post’s publish time, GreyNoise has observed just under seventy IP addresses attempting to exploit this vulnerability: 

Activity started on the 24th and shows no signs of stopping.

Mitigating Harm

Citrix has urged customers to install updated versions of the affected devices as soon as possible. The recommended versions to upgrade to are NetScaler ADC and NetScaler Gateway 14.1-8.50 and later, 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, and NetScaler ADC 12.1-NDcPP 12.1-55.300 and later releases of 12.1-NDcPP.

Citrix has provided no mitigation tips or workarounds at this time. Organizations are urged to patch immediately. The Cybersecurity and Infrastructure Security Agency (CISA) has added an entry for CVE-2023-4966 to its Known Exploited and Vulnerabilities Catalog, which contains detection and mitigation guidance for observed exploitations of CVE-2023-4966 by threat actors against NetScaler ADC and NetScaler Gateway.

Remote access technologies are prime targets for attackers, especially when proof-of-concept code becomes available. GreyNoise Detection Engineers work with research partners, and conducts bespoke vulnerability research to provide timely access to real-time intelligence that can help your organization buy time to patch, remove the noise of opportunistic attackers, and give you the opportunity to focus on fending off targeted attacks.

This article is a summary of the full, in-depth version on the GreyNoise Labs blog.
GreyNoise Labs logo
Link to GreyNoise Twitter account
Link to GreyNoise Twitter account