CriticalCVE-2026-3055

    Insufficient input validation leading to memory overread (CVE-2026-3055)

    Published In CISA KEV since Sources: CVE.org, pwn.watch, CERT-EU, NCSC NZ

    What is affected, what to do

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

    The vulnerability is being actively exploited; treat it as a priority. Update NetScaler ADC to version 66.59, NetScaler ADC to version 62.23, NetScaler ADC to version 37.262. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • NetScaler ADC lt 14.1..66.59
    • NetScaler ADC lt 13.1..62.23
    • NetScaler ADC lt 13.1 FIPS and NDcPP..37.262
    • NetScaler Gateway lt 14.1..66.59
    • NetScaler Gateway lt 13.1..62.23
    Fixed in
    • NetScaler ADC 66.59
    • NetScaler ADC 62.23
    • NetScaler ADC 37.262
    • NetScaler Gateway 66.59
    • NetScaler Gateway 62.23

    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, pwn.watch, CERT-EU, NCSC NZ

    4.0 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 90.6

    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
    230.26 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) 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
    9.3
    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
    4.0 %
    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
    90.6
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    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
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-125

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is reachable over the network without authentication or user interaction, on edge appliances that are internet-facing by design. That puts it in the same class as earlier NetScaler memory-leak bugs that were mass-exploited for session-token theft and initial access. Its exploitation likelihood sits well above the vast majority of published CVEs. CISA has not flagged ransomware use, but typical targets include government, critical-infrastructure operators and enterprises relying on federated SSO. If you expose NetScaler as a SAML IdP, treat this as a P1 emergency change. Without a SAML IdP configuration, a prompt but regular patch cycle is defensible.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Scope exposure: Inventory every NetScaler ADC and NetScaler Gateway instance and check whether it is configured as a SAML IdP. Run show ns version and grep -i "samlIdPProfile" /nsconfig/ns.conf or show authentication samlIdPProfile. Appliances with an active SAML IdP profile go first.
      • Patch:
        • Upgrade 14.1 to 14.1-66.59 or later.
        • Upgrade 13.1 to 13.1-62.23 or later.
        • Upgrade 13.1 FIPS and NDcPP to 13.1-37.262 or later.
        • End-of-life branches (e.g. 12.1, 13.0) receive no fix and must be migrated. Look up the bulletin ID in the Citrix security advisory.
      • Kill sessions after patching: A memory overread can leak session tokens or other memory contents that survive the upgrade. Terminate all sessions:
        • kill aaa session -all
        • kill icaconnection -all
        • kill rdp connection -all
        • kill pcoipConnection -all
        • clear lb persistentSessions
      • If you cannot patch immediately: Temporarily disable the SAML IdP profile or unbind its authentication policy. Alternatively, pull the SAML IdP vServer off the internet if the business can tolerate it.
      • Rotate secrets: If compromise is suspected, rotate the following:
        • the IdP SAML signing certificate and private key
        • LDAP/RADIUS bind accounts
        • local nsroot credentials
      • Check reporting obligations: On confirmed exploitation, start the NIS2 reporting clock (early warning to the national CSIRT/authority within 24 h).

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Restrict management interfaces (NSIP, management SNIP, ports 22/80/443/3010) to a dedicated admin VLAN. Where feasible, limit inbound access to the SAML IdP vServer to known SP ranges or geographies.
      • WAF/IPS: On an upstream WAF or IPS, filter requests to SAML paths (e.g. under /saml/):
        • drop oversized, non-decodable or malformed Base64/Deflate SAMLRequest parameters
        • rate-limit per source IP
        • Pull vendor Suricata/Snort signatures for CVE-2026-3055 as soon as they ship.
      • Configuration hardening:
        • Remove unused SAML IdP profiles.
        • Shorten AAA and Gateway session timeouts.
        • Bind sessions to the client IP where your user base allows it.
      • IAM/least privilege: On federated service providers (M365, SaaS), enforce conditional access, e.g. device compliance and MFA step-up on IP change. This prevents a stolen token from being replayed freely.
      • Integrity check: After patching, hunt for webshells under /var/netscaler/logon/ and /var/vpn/, and for modified cron jobs. If anything is found, rebuild the appliance from a clean image rather than relying on the patch alone.

    3. Runbook step 3

      Detection rules

      • Access logs / ns.log (syslog to SIEM): Bursts of requests to SAML IdP endpoints from single sources, oversized SAMLRequest parameters and unusually large responses to malformed requests. SPL sketch: index=netscaler uri_path="*/saml/*" | stats count avg(bytes_out) by src_ip | where count>100
      • Session hijacking: The same AAA or Gateway session or user appears from different client IPs or ASNs within a short window without a fresh LOGIN event. Correlate SSLVPN LOGIN/AAA events on Client_ip in ns.log.
      • SP side (Entra ID / IdP consumers): Valid SAML sign-ins from atypical IPs or devices. KQL: SigninLogs | where AuthenticationProtocol == "saml20" | summarize dcount(IPAddress) by UserPrincipalName, bin(TimeGenerated,1h) | where dcount_IPAddress > 3
      • Appliance compromise: Unexpected shell activity at the FreeBSD layer (sh/python/curl spawned from httpd), new PHP files in web directories, and NSIP-originated outbound connections to the internet. Spot the latter in Zeek conn.log where id.orig_h is the NSIP and id.resp_h is external.
      • Retro-hunt: Search logs back to at least several weeks before the KEV addition, since exploitation may predate disclosure.

    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

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

    Source: NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE), pwn.watch, certeu_advisory, NCSC NZ (CC BY 4.0)

    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 FIPS and NDcPP – < 37.262
    • 13.1 – < 62.23
    • 14.1 – < 66.59
    • 37.262
    • 62.23
    • 66.59
    NetScalerGateway
    • 14.1 – < 66.59
    • 13.1 – < 62.23
    • 66.59
    • 62.23
    citrixnetscaler_application_delivery_controller
    • 13.1 – < 13.1-37.262
    • 13.1 – < 13.1-62.23
    • 14.1 – < 14.1-60.58
    • 13.1-37.262
    • 13.1-62.23
    • 14.1-60.58
    citrixnetscaler_gateway
    • 14.1 – < 14.1-60.58
    • 13.1 – < 13.1-62.23
    • 14.1-60.58
    • 13.1-62.23

    Vendors and products

    Weakness classes (CWE)

    • CWE-125Out-of-bounds Read

      Base

      The product reads data past the end, or before the beginning, of the intended buffer.

      Entry at MITRE CWE-125

    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
    Reference tagged as exploitlabs.watchtowr.com (opens in a new tab)PoC (publicly reported)reported, not verified—

    References & sources

    • support.citrix.comsupport-home/kbsearch/article?articleNumber=CTX696300Vendor advisory
    • labs.watchtowr.complease-we-beg-just-one-weekend-free-of-appliances-citrix-netsca…Third-party advisory, Exploit, Third-party advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2026-3055government-resource, US government resource
    • pwn.watchpwn.watch: Citrix NetScaler: Citrix NetScaler Out-of-Bounds Read Vulnerabilitypwn-watch
    • support.citrix.comCitrix NetScaler — CVE-2026-3055pwn-watch
    • NVD (NIST)NVD: CVE-2026-3055pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch

    Linked advisories

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    Badge preview for CVE-2026-3055
    <a href="https://intel.neosec.eu/en/cve/CVE-2026-3055"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-3055.svg?lang=en" alt="CVE-2026-3055 – NEOSEC Intel" height="20"></a>