CriticalCVE-2023-6548

    Citrix NetScaler ADC and NetScaler Gateway Code Injection Vulnerability (CVE-2023-6548)

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

    What is affected, what to do

    Improper Control of Generation of Code ('Code Injection') in NetScaler ADC and NetScaler Gateway allows an attacker with access to NSIP, CLIP or SNIP with management interface to perform Authenticated (low privileged) remote code execution on Management Interface.

    The vulnerability is being actively exploited; treat it as a priority. Update Cloud Software Group NetScaler ADC to version 12.35, Cloud Software Group NetScaler ADC to version 51.15, Cloud Software Group NetScaler ADC to version 92.21. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Cloud Software Group NetScaler ADC lt 14.1..12.35
    • Cloud Software Group NetScaler ADC lt 13.1..51.15
    • Cloud Software Group NetScaler ADC lt 13.0..92.21
    • Cloud Software Group NetScaler ADC lt 13.1-FIPS..37.176
    • Cloud Software Group NetScaler ADC lt 12.1-NDcPP..55.302
    • Cloud Software Group NetScaler Gateway lt 14.1..12.35
    • Cloud Software Group NetScaler Gateway lt 13.1..51.15
    • Cloud Software Group NetScaler Gateway lt 13.0..92.21
    Fixed in
    • Cloud Software Group NetScaler ADC 12.35
    • Cloud Software Group NetScaler ADC 51.15
    • Cloud Software Group NetScaler ADC 92.21
    • Cloud Software Group NetScaler ADC 37.176
    • Cloud Software Group NetScaler ADC 55.302
    • Cloud Software Group NetScaler Gateway 12.35
    • Cloud Software Group NetScaler Gateway 51.15
    • Cloud Software Group NetScaler Gateway 92.21

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

    Metrics

    8.8

    Priority

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

    Source: NVD, CVSS v3

    5.5

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: pwn.watch, CVE.org

    3.2 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 88.0

    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
    193.80 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 exploited
    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
    8.8 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
    5.5
    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
    3.2 %
    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
    88.0
    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

    CISA added this flaw to KEV shortly after the vendor disclosure. NetScaler appliances have been a long-standing attacker favourite because they sit on the perimeter and hold credentials and pivot paths into internal networks. Exploitation is network-based and low-complexity, but it requires a valid low-privilege account and reachability of the management interface. Exploitation likelihood is elevated but not extreme, and CISA does not flag ransomware use. If your management interface is reachable via SNIP/CLIP or from the internet, or you rely on weak or shared local accounts, treat this as critical and patch within 24 hours. Where the NSIP is strictly isolated and admin access is MFA-protected, a prompt but scheduled patch cycle is defensible.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Check management interface exposure: Run show ns ip on every appliance and check the Management Access value for each SNIP and CLIP. Any management GUI or SSH (80/443/22) reachable from the internet or from user VLANs is your top priority.

      • Apply the vendor patch:

        • NetScaler ADC/Gateway 14.1 to 14.1-12.35 or later
        • 13.1 to 13.1-51.15 or later
        • 13.0 to 13.0-92.21 or later
        • 13.1-FIPS to 13.1-37.176 or later
        • 12.1-NDcPP to 12.1-55.302 or later

        For release lines not listed (e.g. standard 12.1), check support status in the vendor advisory and migrate to a patched line.

      • Remove management access from SNIP/CLIP now, pending the patch: set ns ip <SNIP/CLIP> -mgmtAccess DISABLED. From then on, administer only via the NSIP from a dedicated admin network.

      • Rotate credentials: Change passwords for nsroot and all local system users. Exploitation needs only low privileges, so read-only and operator accounts matter too. Also rotate any LDAP/RADIUS service account credentials stored on the appliance.

      • Hunt for compromise before and after patching:

        • Look for unknown .php, .sh and .pl files under /netscaler/ns_gui/, /var/netscaler/logon/, /var/vpn/ and /var/tmp/.
        • Review crontabs (/etc/crontab, crontab -l).
        • Check for unexpected system users.
        • If you find anything, treat the appliance as compromised: preserve logs for forensics and rebuild from a clean image.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Place the NSIP in an isolated management VLAN. Firewall rules should allow TCP 22/80/443/3010/3008 to the NSIP only from jump hosts or PAWs. Drop inbound traffic on these ports to SNIP/CLIP at the upstream firewall.
      • On-box ACLs: Use add ns acl / add ns acl6 to restrict management services to defined admin source ranges, then run apply ns acls.
      • IAM / least privilege:
        • Cut local accounts to the minimum.
        • Enforce external authentication with MFA for admin logins.
        • Remove unused command policies and accounts.
        • Review which accounts have shell access.
      • Egress restriction: The NSIP has no need for arbitrary outbound connectivity. Limit egress to NTP, DNS, syslog, LDAP/RADIUS and update sources. This frustrates reverse shells and exfiltration.
      • Central logging: Forward ns.log, httpaccess.log, bash.log and sh.log via syslog to the SIEM. That way the evidence survives even if an attacker wipes local logs.

    3. Runbook step 3

      Detection rules

      • Process ancestry (EDR/auditd where available, otherwise bash.log): httpd, nsppe or PHP processes spawning sh, bash, python, perl, curl or nc. Sigma shape: ParentImage|endswith: '/httpd' AND Image|endswith: ['/sh','/bash','/python','/perl'].
      • Web access log (/var/log/httpaccess.log): POSTs to management endpoints (/nitro/v1/, /menu/, /gui/) from sources outside the admin network. Also flag requests to newly dropped .php files under /vpn/ or /logon/. SPL: index=netscaler sourcetype=httpaccess (uri="*.php" OR uri="/nitro/v1/*") NOT src_ip IN (admin_nets)
      • Authentication events (ns.log): Successful management logins (UI CMD_EXECUTED, AAA LOGIN) by low-privilege accounts via SNIP/CLIP addresses. Off-hours logins and logins right after failed attempts are equally suspicious.
      • File integrity: New or modified files in /netscaler/ns_gui/, /var/netscaler/logon/ and /var/vpn/. Also watch for changes to /etc/crontab and /etc/passwd and for new SUID binaries, e.g. by baselining with find / -newer /flash/nsconfig/ns.conf -type f.
      • Network telemetry (Zeek/Suricata): Outbound connections from NSIP addresses to internet destinations outside approved services, especially to unusual high ports or newly registered domains. Zeek: conn.log where id.orig_h in netscaler_nsip AND NOT id.resp_h in allowed_egress.

    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

    Improper Control of Generation of Code ('Code Injection') in NetScaler ADC and NetScaler Gateway allows an attacker with access to NSIP, CLIP or SNIP with management interface to perform Authenticated (low privileged) remote code execution on Management Interface.

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

    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
    Cloud Software GroupNetScaler ADC
    • 13.0 – < 92.21
    • 12.1-NDcPP – < 55.302
    • 14.1 – < 12.35
    • 13.1-FIPS – < 37.176
    • 13.1 – < 51.15
    • 92.21
    • 55.302
    • 12.35
    • 37.176
    • 51.15
    Cloud Software GroupNetScaler Gateway
    • 14.1 – < 12.35
    • 13.0 – < 92.21
    • 13.1 – < 51.15
    • 12.35
    • 92.21
    • 51.15
    citrixnetscaler_application_delivery_controller
    • 13.0 – < 13.0-92.21
    • 13.1 – < 13.1-37.176
    • 13.1 – < 13.1-51.15
    • 14.1 – < 14.1-12.35
    • 12.1 – < 12.1-55.302
    • 13.0-92.21
    • 13.1-37.176
    • 13.1-51.15
    • 14.1-12.35
    • 12.1-55.302
    citrixnetscaler_gateway
    • 13.1 – < 13.1-51.15
    • 14.1 – < 14.1-12.35
    • 13.0 – < 13.0-92.21
    • 13.1-51.15
    • 14.1-12.35
    • 13.0-92.21

    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

    References & sources

    • support.citrix.comCitrix advisory: CVE-2023-6548Vendor advisory, pwn-watch
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2023-6548government-resource, US government resource
    • pwn.watchpwn.watch: Citrix NetScaler ADC and NetScaler Gateway: 2 actively exploited vulnerabilitiespwn-watch
    • NVD (NIST)NVD: CVE-2023-6548pwn-watch
    • NVD (NIST)NVD: CVE-2023-6549pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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