Citrix Confirms 2 NetScaler Zero-Days After Admins Pulled the Plug

Citrix NetScaler ADC and NetScaler Gateway contain an authentication-bypass vulnerability (CWE-288, 'using an alternate path or channel') that an unauthenticated remote threat actor can exploit. The flaw is triggerable when the appliance is configured as an AAA virtual server or as a Gateway, including SSL VPN, ICA Proxy, CVPN, or RDP Proxy deployments, allowing the attacker to bypass authentication without valid credentials. A successful bypass could give an attacker access to VPN-protected or AAA-gated resources as an authenticated user; no CVSS score has been published yet. Organizations running affected NetScaler appliances in these configurations are exposed, and affected version ranges are not specified in the available data, so defenders should consult Citrix advisory AL26-019. The flaw was added to CISA's KEV on 2026-09-09, indicating exploitation in the wild; ransomware use is unknown, no public PoC is known, and EPSS assigns a 3.4% probability of exploitation within 30 days (88th percentile).

Do: Prioritize applying vendor fixes or mitigations per Citrix advisory AL26-019 in line with CISA BOD 26-04, focusing first on internet-facing appliances configured as AAA virtual servers or Gateways (SSL VPN, ICA Proxy, CVPN, RDP Proxy). Until patched, restrict internet exposure and review VPN/AAA authentication logs for signs of unauthenticated access, following CISA's Forensics Triage Requirements if compromise is suspected.

CVE-2026-65660 is an improper control of code generation (CWE-94) flaw in Microsoft Office SharePoint Server that allows an authenticated, low-privilege attacker to inject and execute arbitrary code over a network. The bug is triggered after login by sending crafted input that SharePoint processes and executes, so any account with basic access to the SharePoint site — including a standard user — is a viable attack path. Successful exploitation yields remote code execution on the SharePoint server with the privileges of the SharePoint service account, threatening full compromise of confidentiality, integrity, and availability (CVSS 8.8). Notably, Microsoft initially classified the flaw as spoofing before it was recharacterized as authenticated RCE, and Canada's Cyber Centre has issued advisory AL26-023 about it. A public proof-of-concept exists on GitHub, but the issue is not in CISA's KEV catalog and there are no confirmed reports of in-the-wild exploitation yet, though EPSS (1.2%, 67th percentile) suggests above-average likelihood of attempted exploitation.

Do: Apply Microsoft's security update for SharePoint Server from the corresponding Patch Tuesday release as soon as possible, prioritizing any server reachable from the internet or exposed to broad internal user populations. Because exploitation only requires an authenticated low-privilege account, review recent SharePoint audit logs for anomalous behavior by ordinary users (unexpected page/app modifications, unusual requests preceding process activity), and enforce least-privilege access so standard accounts cannot reach sensitive site collections. Verify patch levels across all SharePoint farms, including pre-production and forgotten servers, and monitor Microsoft's advisory and the Canadian Cyber Centre's AL26-023 for updates on active exploitation.

CVE-2026-8452 is a memory buffer overflow (CWE-119) in Citrix NetScaler ADC and NetScaler Gateway that applies when the appliance is configured as a Gateway (SSL VPN, ICA Proxy, CVPN, or RDP Proxy) or as an AAA virtual server. The flaw is reachable over the network without authentication (CVSS 4.0: AV:N/PR:N), so an unauthenticated attacker can trigger it remotely. Successful exploitation causes unpredictable or erroneous appliance behavior and denial of service, and the high confidentiality score suggests possible disclosure of memory contents; some reporting suggests pre-authentication remote code execution may be possible, though the vendor description emphasizes DoS. Organizations running affected NetScaler appliances in a Gateway or AAA role — a very common configuration for remote access to Citrix virtual apps and desktops — are potentially exposed. The flaw was added to CISA's KEV catalog on 2026-08-26 and is reported as exploited in the wild, with headlines noting the flaw was already patched before exploitation was confirmed.

Do: Upgrade NetScaler ADC and Gateway to the fixed releases identified in Citrix security advisory AV26-645 (Update 3); no fixed version numbers were included in this data, so consult the advisory directly. Prioritize any appliance with an internet-exposed Gateway (SSL VPN, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server, and given the KEV listing and reports of exploitation, perform log and forensics review for signs of prior compromise per CISA's Forensics Triage Requirements — federal agencies must comply with BOD 26-04 timelines. Where patching cannot happen immediately, restrict or disable exposed Gateway/AAA configurations as an interim mitigation.

CVE-2026-88772 is a critical flaw in Citrix NetScaler ADC and NetScaler Gateway that can lead to remote code execution or denial of service. It is reachable over the network with no privileges and no user interaction, though attack complexity is rated high; successful exploitation can fully compromise the appliance and affect systems behind it. Affected builds are ADC before 14.1-73.37, before 13.1-64.23, before 14.1-73.37 FIPS, and before 13.1.37.279 FIPS and NDcPP, and Gateway before 14.1-73.37 and before 13.1-64.23. Organizations running those releases as internet-facing ADC or VPN gateways are at risk. Citrix-linked reporting describes active zero-day exploitation; no public proof-of-concept is known and the issue is not listed in CISA KEV.

Do: Upgrade NetScaler ADC and Gateway to 14.1-73.37 or 13.1-64.23 (or later), and FIPS/NDcPP ADC builds to 14.1-73.37 FIPS or 13.1.37.279 FIPS and NDcPP (or later). Treat unpatched internet-facing appliances as potentially compromised: review admin and VPN logs, config changes, and unusual processes, and restrict management interfaces until patched.