On Oct. 10, 2023, Citrix released a security bulletin for a sensitive information disclosure vulnerability (CVE-2023-4966) impacting NetScaler ADC and NetScaler Gateway appliances. Mandiant has identified zero-day exploitation of this vulnerability in the wild beginning in late August 2023 as well as n-day exploitation after Citrix’s publication.
Mandiant is investigating multiple instances of successful exploitation of CVE-2023-4966 that resulted in the takeover of legitimate user sessions on NetScaler ADC and Gateway appliances. The session takeovers bypassed password and multi-factor authentication. In this blog post, Mandiant researchers will discuss artifacts that can be used to identify exploitation activity and highlight some of the post exploitation techniques they observed during the incident response investigations.