Citrix NetScaler ADC and Gateway Out-of-Bounds Read (CVE-2025-5777)

Historical catalog analysis: CISA added this entry on July 10, 2025. The entry reflects catalog information retrieved on August 31, 2026, not a snapshot archived on the inclusion date. Check current vendor guidance before acting.

What the vulnerability is

CVE-2025-5777 is an out-of-bounds read vulnerability (CWE-125) affecting Citrix NetScaler ADC and Gateway. The flaw stems from insufficient input validation, which can result in a memory overread. Notably, this vulnerability has been identified as having known use in ransomware campaigns.

Exposure and applicability

This vulnerability is applicable to healthcare organizations utilizing NetScaler for remote access or authentication services. Specifically, exposure exists when the device is configured in any of the following roles:
* Gateway: Including VPN virtual servers, ICA Proxy, CVPN, or RDP Proxy.
* AAA Virtual Server.

Because these components often serve as the primary entry point for clinicians and administrative staff accessing electronic Protected Health Information (ePHI) from remote locations, a compromise of this infrastructure could potentially jeopardize the confidentiality of patient data and the continuity of clinical operations.

Remediation priorities

Based on the reported exploitation by ransomware actors, we analyze the following priority actions for healthcare security leaders:

1. Immediate Patching/Mitigation: Apply vendor-supplied mitigations or updates immediately. Given the link to ransomware, this is the primary defense against initial access.
2. Configuration Audit: Identify all NetScaler instances currently operating as a Gateway or AAA virtual server to determine the exact attack surface within the environment.
3. Cloud Service Review: For organizations utilizing cloud-based delivery of these services, review configurations in alignment with BOD 22-01 guidance to ensure shared responsibility boundaries are addressed.
4. Decommissioning: If mitigations cannot be applied or are unavailable for a specific legacy version, the product should be discontinued to eliminate the risk vector.

How to validate remediation

To verify that exposure has been reduced, security teams and network administrators should:
* Verify Versioning: Confirm that the installed firmware version matches the vendor’s patched release or that specified mitigations are active.
* Configuration Validation: Cross-reference the list of active virtual servers (VPN, ICA Proxy, CVPN, RDP Proxy, AAA) against the applied patches to ensure no unpatched gateways remain active.

Note: A version check alone does not guarantee security, as it does not account for potential misconfigurations or other vulnerabilities.

Limits and open questions

While the vulnerability is confirmed to allow memory overreads, the full extent of what data can be extracted from memory remains an open question. It is not explicitly stated in the source whether this flaw allows for remote code execution (RCE) or if it is primarily used for information disclosure to facilitate further attacks. Additionally, while ransomware use is confirmed, the specific targets and methods of lateral movement following a successful overread are not detailed.

Source and editorial note

CVE-2025-5777: Citrix NetScaler ADC and Gateway Out-of-Bounds Read Vulnerability · Source date: July 10, 2025 · Retrieved August 31, 2026.

Material facts are tied to the cited primary source. Recommendations are independent defensive analysis unless attributed to the source. Confirm consequential decisions against current authoritative guidance.

Archive date: July 13, 2025. The displayed post date is assigned three days after the source date to organize this retrospective archive; it does not mean this site published the analysis then. First published by this site: October 06, 2026 at 00:50 UTC.

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