CriticalCVE-2023-3519

    Citrix NetScaler ADC and NetScaler Gateway Code Injection Vulnerability (CVE-2023-3519)

    Published In CISA KEV since Sources: pwn.watch, CVE.org

    What is affected, what to do

    Unauthenticated remote code execution

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Citrix NetScaler ADC to version 49.13, Citrix NetScaler ADC to version 91.13, Citrix NetScaler ADC to version 37.159. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Citrix NetScaler ADC lt 13.1..49.13
    • Citrix NetScaler ADC lt 13.0..91.13
    • Citrix NetScaler ADC lt 13.1-FIPS..37.159
    • Citrix NetScaler ADC lt 12.1-NDcPP..55.297
    • Citrix NetScaler Gateway lt 13.1..49.13
    • Citrix NetScaler Gateway lt 13.0..91.13
    Fixed in
    • Citrix NetScaler ADC 49.13
    • Citrix NetScaler ADC 91.13
    • Citrix NetScaler ADC 37.159
    • Citrix NetScaler ADC 55.297
    • Citrix NetScaler Gateway 49.13
    • Citrix NetScaler Gateway 91.13

    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: pwn.watch, CVE.org

    99.75 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.96

    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
    257.04 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: CERT.at, ANSSI / CERT-FR 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
    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
    99.75 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    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
    99.96
    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-94

    Response and mitigation

    Why act now?

    Prioritisation rationale

    CVE-2023-3519 scores CVSS 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) and sits at the 100th EPSS percentile, meaning virtually every exploitation model rates it as near-certain to be actively used — which CISA confirms with its known-ransomware-campaign flag. Attackers exploit the vulnerability to drop persistent webshells without any authentication, then pivot laterally toward Active Directory and backend systems reachable through the NetScaler. The primary target profile is exactly the infrastructure in NIS2 and KRITIS scope: organisations running NetScaler as a remote-access VPN gateway or Citrix Virtual Apps and Desktops entry point. Any unpatched instance configured as a Gateway or AAA server must be treated as the highest-priority remediation item in the current patch cycle, ahead of all lower-severity findings.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Apply the vendor patch immediately — Citrix has released fixes for all affected branches. Target versions: NetScaler ADC and Gateway 13.1-49.13+, 13.0-91.13+, 12.1-55.297+. Full patch details are in Citrix Security Bulletin CTX561482.
      • Isolate any appliance configured as a Gateway (VPN, ICA Proxy, RDP Proxy) or AAA server if the patch cannot be deployed within two hours. Pure ADC instances without these roles are not directly exploitable via this vector.
      • Hunt for webshell artefacts — Citrix provides a forensic script linked in CTX561482. Manually check /netscaler/ns_gui/vpn/ and /var/netscaler/logon/ for unexpected .php, .cgi, or .pl files. Treat any unknown file as a confirmed indicator of compromise.
      • Rotate all credentials stored on or authenticated through the appliance: local admin accounts, LDAP/RADIUS service accounts, API tokens, and any secrets in session policies. Successful exploitation grants full OS-level access.
      • Restrict the NetScaler management interface (NSIP, port 80/443) to a dedicated management VLAN and remove it from any internet-facing path if not already done.

    2. Runbook step 2

      Mitigation layers

      • Deploy a WAF or IPS rule upstream of the NetScaler: block or alert on requests containing path-traversal sequences (/../, %2F..%2F) targeting /vpn/, /gwtest/, or /logon/. Suggested Suricata shape: alert http any any -> $NETSCALER_IP any (msg:"CVE-2023-3519 exploit attempt"; content:"/vpn/"; http_uri; content:"/../"; http_uri; sid:2023351901;).
      • Restrict outbound connections from the NSIP to a known-good allowlist (DNS, NTP, Syslog, LDAP/LDAPS). This limits attacker ability to establish C2 callbacks after successful RCE.
      • Enforce least-privilege on LDAP/RADIUS service accounts configured on the appliance — read-only directory access only, no Domain Admin or equivalent rights.
      • Stream logs to an external SIEM over TLS Syslog — compromised appliances frequently have local logs tampered with. Ensure /var/log/ns.log and /var/log/httperror.log are forwarded continuously before any remediation work begins.
      • Prioritise migration of 12.1 instances: version 12.1 is end-of-life with no further security support. Schedule migration to 13.1 as a tracked project with a deadline under 30 days.

    3. Runbook step 3

      Detection rules

      • NetScaler access and error logs (/var/log/httperror.log, /var/log/ns.log): flag HTTP requests containing path-traversal patterns (/../, %2F..%2F) to /vpn/, /gwtest/, or /logon/ that return HTTP 200 with an unusually large response body.
      • Filesystem integrity monitoring: alert on new or modified files with extensions .php, .cgi, .pl under /netscaler/ns_gui/vpn/, /var/netscaler/logon/, /var/tmp/. Auditd rule: -w /netscaler/ns_gui/vpn/ -p wa -k cve_2023_3519_webshell.
      • Process ancestry anomalies: unexpected child processes spawned by httpd or nsppe — specifically sh, curl, wget, python, or perl. EDR/process-tree alert: parent httpd → child sh or any process initiating an outbound network connection.
      • Network telemetry (Zeek conn.log): outbound connections from the NSIP to unknown external IPs on non-standard ports. Filter: id.orig_h == <NSIP> AND id.resp_p NOT IN {53, 80, 123, 389, 443, 636}.
      • Sigma rule shape: title: CVE-2023-3519 NetScaler Webshell Access | logsource: product: netscaler | detection: keywords: ['/vpn/../', '/gwtest/formssso', 'cmd='] | condition: keywords.

    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

    Unauthenticated remote code execution

    Source: pwn.watch, CISA KEV Catalog, cvelistv5, NVD (NIST), CVE.org (MITRE)

    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
    CitrixNetScaler ADC
    • 13.1 – < 49.13
    • 13.1-FIPS – < 37.159
    • 13.0 – < 91.13
    • 12.1-NDcPP – < 55.297
    • 49.13
    • 37.159
    • 91.13
    • 55.297
    CitrixNetScaler Gateway
    • 13.0 – < 91.13
    • 13.1 – < 49.13
    • 91.13
    • 49.13
    citrixnetscaler_application_delivery_controller
    • 13.1 – < 13.1-37.159
    • 13.0 – < 13.0-91.13
    • 12.1 – < 12.1-55.297
    • 13.1 – < 13.1-49.13
    • 13.1-37.159
    • 13.0-91.13
    • 12.1-55.297
    • 13.1-49.13
    citrixnetscaler_gateway
    • 13.0 – < 13.0-91.13
    • 13.1 – < 13.1-49.13
    • 13.0-91.13
    • 13.1-49.13

    Vendors and products

    Weakness classes (CWE)

    • CWE-94Improper Control of Generation of Code ('Code Injection')

      Base

      The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.

      Entry at MITRE CWE-94

    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
    ANSSI / CERT-FRLicence Ouverte 2.0, as of CERTFR-2023-ALE-008 – [MàJ] Vulnérabilité dans Citrix NetScaler ADC et NetScaler Gateway (clôturée 2024-01-02) (opens in a new tab)cert.cyber.gouv.fractively exploited
    Packet StormCitrix ADC NetScaler Remote Code Execution (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—

    References & sources

    • support.citrix.comarticle/CTX561482/citrix-adc-and-citrix-gateway-security-bullet…
    • packetstormsecurity.comfiles/173997/Citrix-ADC-NetScaler-Remote-Code-Execution.html
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2023-3519government-resource
    • cert.atCERT.at: Update #1 - Sicherheitslücken, teils kritisch, in Citrix/Netscaler ADC und Gateway - aktiv ausgenützt - Updates verfügbarcert-at
    • cert.cyber.gouv.frANSSI / CERT-FR: CERTFR-2023-ALE-008 – [MàJ] Vulnérabilité dans Citrix NetScaler ADC et NetScaler Gateway (clôturée 2024-01-02)cert-fr
    • pwn.watchpwn.watch: NetScaler ADC/Gateway unauthenticated RCE (CVE-2023-3519)pwn-watch
    • support.citrix.comCitrix ADC and Citrix Gateway Security Bulletin for CVE-2023-3519, CVE-2023-3466, CVE-2023-3467pwn-watch
    • cisa.govThreat Actors Exploiting Citrix CVE-2023-3519 to Implant Webshells (AA23-201A)pwn-watch
    • NVD (NIST)NVD: CVE-2023-3519pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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    Badge preview for CVE-2023-3519
    <a href="https://intel.neosec.eu/en/cve/CVE-2023-3519"><img src="https://intel.neosec.eu/badge/cve/CVE-2023-3519.svg?lang=en" alt="CVE-2023-3519 – NEOSEC Intel" height="20"></a>