Vulnerabilities

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.

xrdp is an open source RDP server. Versions 0.10.6 and prior contain a missing bounds check in xrdp, which allows a heap-based buffer overflow when operating in vnc-any mode. The issue occurs during the handling of RFB protocol color map messages from a VNC server, where incoming color indices are not properly validated. A malicious VNC server can exploit this flaw by sending crafted messages with out-of-range values, leading to an out-of-bounds write on the heap. This memory corruption can result in a denial of service (DoS) or potentially allow remote code execution (RCE) prior to authentication. This issue has been fixed in version 0.10.6.1.

Insufficient input validation in NetScaler ADC and NetScaler Gateway leading to memory overread if NetScaler ADC or NetScaler Gateway is configured as a SAML IDP

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.

CWE-476 NULL Pointer Dereference vulnerability exists that could cause a denial-of-service condition, rendering the device’s HMI and configuration functionality unavailable when malformed requests are received over exposed network interfaces.

CWE-522 Insufficiently Protected Credentials vulnerability that could cause unauthorized access and exposure of sensitive information when unauthenticated attacker accesses credentials stored within firmware or system files. With this credential an attacker could subsequently compromise the device if they have physical access to the device.