CriticalCVE-2026-8452

    Memory overflow vulnerability leading to unpredictable or erroneous behavior and Denial of Service (CVE-2026-8452)

    Published Last modified In CISA KEV since Sources: CVE.org, NCSC NZ, BSI

    What is affected, what to do

    A buffer overflow vulnerability in Citrix NetScaler ADC and NetScaler Gateway can lead to a Denial of Service (DoS) if the appliance is configured as a Gateway (SSL VPN, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server. The vulnerability is actively exploited in the wild and affects specific product versions. Affected versions include NetScaler ADC 13.1-37.272 to 14.1-72.61 and NetScaler Gateway 13.1 to 14.1-72.61. Immediate patching is necessary to mitigate the risk.

    The vulnerability is being actively exploited; treat it as a priority. Update NetScaler ADC to version 63.18, NetScaler ADC to version 72.61, NetScaler ADC to version 37.272. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • NetScaler ADC lt 13.1..63.18
    • NetScaler ADC lt 14.1 FIPS..72.61
    • NetScaler ADC lt 13.1 FIPS and NDcPP..37.272
    • NetScaler Gateway lt 14.1..72.61
    • NetScaler Gateway lt 13.1..63.18
    Fixed in
    • NetScaler ADC 63.18
    • NetScaler ADC 72.61
    • NetScaler ADC 37.272
    • NetScaler Gateway 72.61
    • NetScaler Gateway 63.18

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.8

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: CVE.org, NCSC NZ, BSI

    1.0 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 62.9

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    200.74 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: VulnCheck KEV (opens in a new tab), NCSC NZ How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.8 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.8
    CVSS v4

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    8.8
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    1.0 %
    Moderate — model estimates 1-10% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    62.9
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is reachable over the network with no authentication or user interaction, and it sits in the component organisations deliberately expose to the internet: the remote-access gateway / AAA server. Its statistical exploitation likelihood looks only moderate, and CISA lists no known ransomware use. Even so, KEV inclusion confirms real-world attacks, and NetScaler gateways have repeatedly been top targets for mass scanning. For NIS2/KRITIS entities whose remote maintenance or workforce access runs through NetScaler, a forced outage is a direct availability and incident-reporting risk. Treat internet-facing Gateway/AAA instances as P1 (patch within 24-48 h). Internal-only ADC instances without Gateway/AAA configuration can follow the regular patch cycle.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Scope your exposure: Run show version on every NetScaler and grep ns.conf for add vpn vserver / add authentication vserver. Only appliances configured as a Gateway (SSL VPN, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server are vulnerable. Internet-facing gateways come first.

      • Patch: Upgrade NetScaler ADC/Gateway as follows:

        • 14.1 to 14.1-72.61 or later
        • 13.1 to 13.1-63.18 or later
        • 13.1 FIPS/NDcPP to 13.1-37.272 or later
        • 14.1 FIPS to 14.1-72.61 or later

        For build 14.1-66.68 listed in the context, a patch is available from the vendor — check the vendor advisory for the exact fixed version.

      • Roll HA pairs safely: Patch the secondary, fail over, then patch the former primary so remote access stays up throughout.

      • Find unsupported branches: End-of-life builds will not receive a fix. Migrate them to a supported release line or pull them off the internet.

      • Kill sessions post-patch (precautionary): The vendor describes this as DoS-only, but past NetScaler gateway memory bugs have leaked session material. After upgrading, run kill aaa session -all, kill icaconnection -all, kill rdp connection -all and kill pcoipConnection -all.

      • Preserve evidence: Collect /var/core/ and /var/log/ns.log* before upgrading. Crash artefacts are your best proof of pre-patch exploitation.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Restrict NSIP and any management-enabled SNIP to a dedicated admin VLAN. If the gateway does not need to be reachable from the whole internet, limit TCP/443 on the Gateway vServer with geo/IP allowlists covering known employee and partner ranges.
      • Upstream WAF/IPS: Inspect requests to Gateway/AAA endpoints (e.g. /p/u/doAuthentication.do, /nf/auth/, /vpn/, /cgi/login) for oversized headers, cookies and bodies. Drop anything above an operationally justified ceiling (e.g. headers > 8 KB) and apply per-source-IP rate limits on these paths.
      • Configuration hardening: Disable unused gateway features (CVPN, RDP Proxy, ICA Proxy) and idle AAA vServers with disable vpn vserver <name> / disable authentication vserver <name>. Every disabled feature removes attack surface.
      • Availability resilience: Confirm HA health and auto-failover. Document and test a fallback remote-access path (e.g. a separate VPN concentrator) so your BCM plan holds if the gateway is knocked over.
      • IAM: Enforce MFA on the gateway and shorten session timeouts to reduce the value of any exposed session data.

    3. Runbook step 3

      Detection rules

      • Packet-engine crashes: Watch for new core dumps under /var/core/<n>/NSPPE-* and ns.log entries for packet-engine restarts. SPL: index=netscaler sourcetype=ns:log ("NSPPE" AND ("core" OR "restart" OR "crash")).
      • Unplanned HA failovers: Alert on SNMP trap haNodeStateChange or ns.log HA state changes outside maintenance windows. Repeated failovers in a short window are a strong signal.
      • Access-log anomalies: In HTTP/WAF/reverse-proxy logs in front of the NetScaler, look for unusually large or malformed requests to Gateway/AAA paths. Sigma shape: logsource: webserver with cs-uri-stem|contains: ['/p/u/doAuthentication.do','/nf/auth/','/vpn/'] and cs-bytes > 8000.
      • Network telemetry: Use Zeek/Suricata to flag bursts of TLS connections from a single source to the gateway VIP, especially when followed by resets or timeouts. KQL: CommonSecurityLog | where DestinationIP == "<gw_vip>" | summarize count() by SourceIP, bin(TimeGenerated,1m) | where count_ > 300.
      • Session anomalies (precautionary): Flag the same AAA session ID appearing from multiple source IPs or geolocations, using gateway session logging in ns.log (SSLVPN LOGIN, TCPCONNSTAT).

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    Memory overflow vulnerability NetScaler ADC and NetScaler Gateway leading to unpredictable or erroneous behavior and Denial of Service if the appliance is configured as a Gateway (SSL VPN, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server

    Source: CISA KEV Catalog, NVD (NIST), CVE.org (MITRE), cvelistv5, NCSC NZ (CC BY 4.0), BSI WID Portal, BSI CSAF

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    NetScalerADC
    • 13.1 – < 63.18
    • 13.1 FIPS and NDcPP – < 37.272
    • 14.1 FIPS – < 72.61
    • 63.18
    • 37.272
    • 72.61
    NetScalerGateway
    • 14.1 – < 72.61
    • 13.1 – < 63.18
    • 72.61
    • 63.18
    citrixnetscaler_application_delivery_controller
    • 14.1 – < 14.1-72.61
    • < 13.1-37.272
    • 14.1-66.68
    • 13.1 – < 13.1-63.18
    • 14.1-72.61
    • 13.1-37.272
    • —
    • 13.1-63.18
    citrixnetscaler_gateway
    • 14.1 – < 14.1-72.61
    • 13.1 – < 13.1-63.18
    • 14.1-72.61
    • 13.1-63.18
    Citrix SystemsNetScaler
    • ADC <13.1-FIPS 13.1.37.272
    • ADC <13.1-NDcPP 13.1.37.272
    • ADC <14.1-72.61 FIPS
    • —
    • —
    • —
    Citrix SystemsNetScaler ADC
    • < 14.1-72.61
    • < 13.1-63.18
    • 14.1-72.61
    • 13.1-63.18
    Citrix SystemsNetScaler Gateway
    • < 13.1-63.18
    • < 14.1-72.61
    • 13.1-63.18
    • 14.1-72.61

    Vendors and products

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    NCSC NZMultiple vulnerabilities affecting Citrix NetScaler ADC and NetScaler Gateway products (opens in a new tab)NCSC NZactively exploited
    PoC-in-GitHub (nomi-sec)citrix-netscaler-cve-2026-8452-rce (opens in a new tab)github.comPoC (publicly reported)reported, not verified
    PoC-in-GitHub (nomi-sec)CitrixBleedCVE-2026-8452-2025-5777 (opens in a new tab)github.comPoC (publicly reported)reported, not verified
    PoC-in-GitHub (nomi-sec)CVE-2026-8452-check (opens in a new tab)github.comPoC (publicly reported)reported, not verified
    PoC-in-GitHub (nomi-sec)watchTowr-vs-Citrix-Netscaler-PreAuth-RCE-CVE-2026-8452 (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    References & sources

    • support.citrix.comsupport-home/kbsearch/article?articleNumber=CTX696604
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2026-8452government-resource

    Reanalysis & status changes

    Chronological NVD audit events for this CVE — reanalyses, CVSS updates, CPE diffs.

    1. Modified Analysisnvd@nist.gov

      • Reference Type: after CISA-ADP: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-8452 Types: US Government Resource

    2. CVE CISA KEV Update9119a7d8-5eab-497f-8521-727c672e3725

      • Date Added: after 2026-08-26
      • Due Date: after 2026-08-26
      • Required Action: after 2026-08-26
      • Vulnerability Name: after 2026-08-26

    3. CVE Modified50a63c94-1ea7-4568-8c11-eb79e7c5a2b5

      • Reference: after https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX696604
      • Reference: before https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX696604
      • Reference Type: before https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX696604 Types: Vendor Advisory

    4. CVE Modified134c704f-9b21-4f2e-91b3-4a467353bcc0

      • Reference: after https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-8452
      • SSVC: before {"id":"CVE-2026-8452","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalI… after {"id":"CVE-2026-8452","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"yes"},{"technica…

    Linked advisories

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