Hackers Exploit Two Critical Citrix NetScaler Zero-Days to Deploy Web Shells and Enable Lateral Movement

Two critical zero-day vulnerabilities in Citrix NetScaler, tracked as CVE-2026-88771 and CVE-2026-88772, are being actively exploited in the wild to achieve unauthenticated remote code execution. Attackers deploy password-protected PHP web shells such as WHIPSHOT and use the Python-based SLAPSHOT tunneling tool for lateral movement inside targeted networks. The flaws affect NetScaler ADC and NetScaler Gateway appliances with default configurations, and one requires DTLS enabled on VPN vServers. Citrix has released patches for versions 13.1-64.23 and 14.1-73.37, while CISA added the issues to its KEV catalog with a September 30, 2026 remediation deadline for U.S. federal agencies. Organizations are advised to hunt for indicators including modified httpd.conf entries, anomalous setuid permissions on /bin/sh, and suspicious files in /var/netscaler/logon/LogonPoint/custom before applying updates.

HispasecSeptember 30, 2026Translated from Spanish

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Threat actors are actively exploiting two critical zero-day vulnerabilities in Citrix NetScaler appliances to gain unauthenticated remote code execution, deploy stealthy web shells, and move laterally across compromised networks.

The vulnerabilities, identified as CVE-2026-88771 and CVE-2026-88772, both carry a CVSS v4.0 score of 9.5. CVE-2026-88771 stems from improper input validation and affects default deployments of NetScaler ADC and NetScaler Gateway. CVE-2026-88772 results from a memory overflow that can lead to RCE or denial of service when DTLS is enabled, a setting active by default on many VPN vServers.

Attackers have moved beyond proof-of-concept exploits. They install password-protected PHP web shells and modify web server configurations so that files with seemingly harmless extensions such as .css or image files are processed as PHP scripts. This technique hinders manual detection and allows malicious payloads to blend with legitimate resources.

Additional persistence techniques include setting the setuid bit on /bin/sh to grant root privileges to commands executed through the web shell. Observed artifacts include the file /var/netscaler/logon/LogonPoint/custom/.ctxs.receiver, suspicious Alias or AliasMatch directives in httpd.conf, and Python processes launched with nohup alongside files such as /tmp/.uxdport and /tmp/.uxdlock.

The campaign has been linked to the WHIPSHOT PHP web shell and the SLAPSHOT TCP tunneling tool written in Python. Citrix has issued patches for NetScaler ADC 13.1 before 13.1-64.23 and 14.1 before 14.1-73.37, along with corresponding NetScaler Gateway builds and FIPS/NDcPP variants. CISA has added both CVEs to its Known Exploited Vulnerabilities catalog and set a September 30, 2026 deadline for federal agencies.

NetScaler Gateway CVE-2026-88771 CVE-2026-88772 WHIPSHOT SLAPSHOT Citrix NetScaler ADC

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