CriticalCVE-2026-88773

    HTTP Request Smuggling (CVE-2026-88773)

    Published Last modified Sources: NCSC UK, NCSC NZ, SingCERT, CERT-EU, pwn.watch, BSI, CVE.org

    What is affected, what to do

    Inconsistent interpretation of HTTP requests ('HTTP Request/Response smuggling') vulnerability in Citrix NetScaler ADC and Citrix NetScaler Gateway. This issue affects ADC: before 14.1-73.37, before 13.1-64.23, before 14.1-73.37 FIPS, and before 13.1-37.279 and NDcPP; Gateway: before 14.1-73.37 FIPS and before 13.1-64.23.

    The vulnerability is being actively exploited; treat it as a priority. Update Citrix NetScaler ADC to version 14.1-73.37, Citrix NetScaler ADC to version 13.1-64.23, Citrix NetScaler Gateway to version 13.1-64.23.

    Affected
    • Citrix NetScaler ADC lt *..14.1-73.37
    • Citrix NetScaler ADC lt *..13.1-64.23
    • Citrix NetScaler Gateway lt *..13.1-64.23
    Fixed in
    • Citrix NetScaler ADC 14.1-73.37
    • Citrix NetScaler ADC 13.1-64.23
    • Citrix NetScaler Gateway 13.1-64.23

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

    Metrics

    10.0

    Priority

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

    Source: NVD, CVSS v3

    10.0

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: NCSC UK, NCSC NZ, SingCERT, CERT-EU, pwn.watch, BSI, CVE.org

    3.4 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 88.7

    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
    142.50 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, 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
    10.0 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
    10.0
    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
    3.4 %
    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
    88.7
    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
    —
    Published
    CISA assessment (SSVC)
    Exploitation: none known · automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 29 September 2026
    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-444

    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

    Inconsistent interpretation of HTTP requests ('HTTP Request/Response smuggling') vulnerability in Citrix NetScaler ADC and Citrix NetScaler Gateway. This issue affects ADC: before 14.1-73.37, before 13.1-64.23, before 14.1-73.37 FIPS, and before 13.1-37.279 and NDcPP; Gateway: before 14.1-73.37 FIPS and before 13.1-64.23.

    Source: NCSC UK (OGL v3.0), NCSC NZ (CC BY 4.0), CSA/SingCERT, certeu_advisory, pwn.watch, BSI WID Portal, BSI CSAF, 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
    Citrix NetScalerADC
    • < 14.1-73.37
    • < 13.1-64.23
    • 14.1-73.37
    • 13.1-64.23
    Citrix NetScalerGateway
    • < 13.1-64.23
    • 13.1-64.23
    citrixnetscaler_application_delivery_controller
    • 13.1 – < 13.1-64.23
    • 14.1-66.68 – ≤ 14.1-73.37
    • 14.1 – < 14.1-73.37
    • 13.1 – < 13.1.37.279
    • 13.1-64.23
    • —
    • 14.1-73.37
    • 13.1.37.279
    citrixnetscaler_gateway
    • 14.1 – < 14.1-73.37
    • 13.1 – < 13.1-64.23
    • 14.1-73.37
    • 13.1-64.23
    Citrix SystemsNetScaler ADC
    • < 14.1-73.37
    • < 13.1-64.23
    • 14.1-73.37
    • 13.1-64.23
    Citrix SystemsNetScaler ADC FIPS
    • < 13.1-37.279
    • < 14.1-73.37
    • 13.1-37.279
    • 14.1-73.37
    Citrix SystemsNetScaler ADC NDcPP
    • < 13.1-37.279
    • 13.1-37.279
    Citrix SystemsNetScaler Gateway
    • < 13.1-64.23
    • < 14.1-73.37
    • 13.1-64.23
    • 14.1-73.37

    Vendors and products

    Weakness classes (CWE)

    • CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

      Base

      The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.

      Entry at MITRE CWE-444

    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
    NCSC NZUPDATED: Multiple vulnerabilities affecting Citrix NetScaler ADC and NetScaler Gateway products (opens in a new tab)NCSC NZactively exploited
    PoC-in-GitHub (nomi-sec)CVE-2026-88773 (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    References & sources

    • support.citrix.comsupport-home/kbsearch/article?articleNumber=CTX697096
    • cert.atCERT.at: Kritische Sicherheitslücken in Citrix NetScaler ADC und NetScaler Gateway - aktiv ausgenutzt - Updates verfügbarcert-at
    • pwn.watchpwn.watch: Citrix NetScaler ADC and Gateway: two unauthenticated RCE zero-days under active exploitation (CVE-2026-88771, CVE-2026-88772)pwn-watch
    • support.citrix.comCitrix NetScaler ADC and Citrix NetScaler Gateway Security Bulletin for CVE-2026-88771 through CVE-2026-88778 (CTX697096)pwn-watch
    • support.citrix.comCitrix NetScaler ADC and Citrix NetScaler Gateway Security Bulletin for CVE-2026-107406 (CTX697191)pwn-watch
    • cisa.govCritical Zero-Day Vulnerabilities Exploited in Citrix NetScaler ADC, Gatewaypwn-watch
    • cyber.gc.caAL26-024: Critical vulnerabilities affecting Citrix NetScaler ADC and NetScaler Gatewaypwn-watch
    • cert.europa.euCERT-EU 2026-014: Critical Vulnerabilities in Citrix NetScaler ADC and Gatewaypwn-watch
    • rapid7.comRapid7 Analysis: NetScaler intrusions chaining CVE-2026-88771 and CVE-2026-88779pwn-watch
    • cybersecuritytimes.comZscaler Detects Coordinated Exploitation Attempts Targeting Critical NetScaler RCE Flawpwn-watch
    • JPCERT/CCJPCERT/CC JPCERT-AT-2026-0029: NetScaler ADCおよびNetScaler Gatewayにおける複数の脆弱性（CVE-2026-88771、CVE-2026-88772等）に関する注意喚起jpcert

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: yes

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2026-88773","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-09-29T15:17:32.077580Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. Initial analysis by NVDNVD

      Newly listed as affected:

      CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

      Show 3 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
      Product configurationadded
      —
      OR *cpe:2.3:a:citrix:netscaler_application_delivery_controller:*:*:*:*:-:*:*:* versions from (including) 13.1 up to (excluding) 13.1-64.23 *cpe:2.3:a:citrix:netscaler_application_delivery_controller:*:*:*:*:-:*:*:* versions from (including) 14.1 up to (excluding) 14.1-73.37 *cpe:2.3:a:citrix:netscaler_application_delivery_controller:*:*:*:*:fips:*:*:* versions from (including) 13.1 up to (excluding) 13.1.37.279 *cpe:2.3:a:citrix:netscaler_application_delivery_controller:*:*:*:*:fips:*:*:* versions from (including) 14.1-66.68 up to (including) 14.1-73.37 *cpe:2.3:a:citrix:netscaler_application_delivery_controller:*:*:*:*:ndcpp:*:*:* versions from (including) 13.1 up to (excluding) 13.1.37.279 *cpe:2.3:a:citrix:netscaler_gateway:*:*:*:*:*:*:*:* versions from (including) 13.1 up to (excluding) 13.1-64.23 *cpe:2.3:a:citrix:netscaler_gateway:*:*:*:*:*:*:*:* versions from (including) 14.1 up to (excluding) 14.1-73.37
      Reference typeadded
      —
      NetScaler: https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX697096 Types: Vendor Advisory

      Source identifier: nvd@nist.gov

    3. Received50a63c94…

      CVSS V4.0: AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:H/SI:H/SA:N

      Weakness type: CWE-444

      Description added or changed

      Show 5 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      Inconsistent interpretation of HTTP requests ('HTTP Request/Response smuggling') vulnerability in Citrix NetScaler ADC and Citrix NetScaler Gateway. This issue affects ADC: before 14.1-73.37, before 13.1-64.23, before 14.1-73.37 FIPS, and before 13.1-37.279 and NDcPP; Gateway: before 14.1-73.37 FIPS and before 13.1-64.23.
      CVSSadded
      —
      AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
      Weakness type (CWE)added
      —
      CWE-444
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/88xxx/CVE-2026-88773.json">CVE-2026-88773</a>
      Referenceadded
      —
      https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX697096

      Source identifier: 50a63c94-1ea7-4568-8c11-eb79e7c5a2b5

    One NVD translation into another language is hidden.

    Linked advisories

    Embed badge

    Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

    Badge preview for CVE-2026-88773
    <a href="https://intel.neosec.eu/en/cve/CVE-2026-88773"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-88773.svg?lang=en" alt="CVE-2026-88773 – NEOSEC Intel" height="20"></a>