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Full vulnerability report · 2026
CVE-2026-88778High confidence

TCP Initial Sequence Number (ISN) prediction

Citrix NetScaler · ADC

8.8HighCVSS 4.0
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Mitigation available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:High, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 0.38% for the current model date.

Compensating controls

  • Apply the linked authoritative mitigation while planning the permanent fix.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Citrix NetScaler ADC and falls inside the recorded affected range.
  2. Recheck the vendor advisory before scheduling a change because no verified fixed version is currently retained.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 30 daysRemediation target: Within 180 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-87973

No EUVD known-exploited evidence

Predictable exact value from previous values 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 FIPS and NDcPP; Gateway: before 14.1-73.37 and before 13.1-64.23.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
8.8 · CVSS 4.0
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Mitigation available
01

What, why and how

Predictable exact value from previous values 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 FIPS and NDcPP; Gateway: before 14.1-73.37 and before 13.1-64.23.

What

Predictable exact value from previous values 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 FIPS and NDcPP; Gateway: before 14.1-73.37 and before 13.1-64.23.

Why

An exact value or random number can be precisely predicted by observing previous values.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

Predictable exact value from previous values 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 FIPS and NDcPP; Gateway: before 14.1-73.37 and before 13.1-64.23.

Why

An exact value or random number can be precisely predicted by observing previous values.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Predictable Exact Value from Previous Values → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Not a CVSS 4.0 base metric
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-342 ↗

CWE-342: Predictable Exact Value from Previous Values. An exact value or random number can be precisely predicted by observing previous values.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:H/SC:L/SI:L/SA:L

Common Vulnerability Scoring System 4.0: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.ATNoneAttack requirements: No additional deployment or execution condition is required.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.VCLowVulnerable-system confidentiality: A successful attack can cause a limited loss.VIHighVulnerable-system integrity: A successful attack can cause a major loss.VAHighVulnerable-system availability: A successful attack can cause a major loss.SCLowSubsequent-system confidentiality: A successful attack can cause a limited loss.SILowSubsequent-system integrity: A successful attack can cause a limited loss.SALowSubsequent-system availability: A successful attack can cause a limited loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-342
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-87973Official EUVD mapping

Predictable exact value from previous values 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 FIPS and NDcPP; Gateway: before 14.1-73.37 and before 13.1-64.23.

Official EUVD record ↗
BSI · German · WID-SEC-2026-3587Citrix NetScaler ADC und Citrix NetScaler Gateway: Mehrere Schwachstellen

Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Citrix NetScaler ADC und Citrix NetScaler Gateway ausnutzen, um beliebigen Code auszuführen, einen Denial-of-Service-Zustand auszulösen, Daten zu manipulieren, Sicherheitsmaßnahmen zu umgehen und weitere, nicht näher bezeichnete Auswirkungen zu erzielen.

Official advisory ↗
Canadian Centre for Cyber Security · English · AV26-965Citrix security advisory (AV26-965)

As of September 27, 2026, Citrix is affected by vulnerabilities in the following products:

Official advisory ↗
Canadian Centre for Cyber Security · English · AL26-024AL26-024 - Critical vulnerabilities affecting Citrix NetScaler ADC and NetScaler Gateway – CVE-2026-88771 and CVE-2026-88772 – Update 1

An Alert is used to raise awareness of a recently identified cyber threat that may impact cyber information assets, and to provide additional detection and mitigation advice to recipients. The Canadian Centre for Cyber Security ("Cyber Centre") is also available to provide additional assistance regarding the content of this Alert to recipients as requested.

Official advisory ↗
INCIBE-CERT · Spanish · multiples-vulnerabilidades-en-productos-de-citrix-1Múltiples vulnerabilidades en productos de Citrix

Michael Tucker, Chew Keong Tan, Alex Bernier y Maxim Suhanov han informado sobre 8 vulnerabilidades: 3 de severidad crítica y 5 de severidad alta que, en caso de ser explotadas, podrían permitir la ejecución remota de código, la denegación de servicio (DoS), el contrabando de peticiones HTTP, la evasión de políticas de seguridad o la predicción de números de secuencia TCP. Citrix ha confirmado la explotación activa de CVE-2026-88771 y CVE-2026-88772 en instalaciones de NetScaler que no habían sido actualizadas.

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-1235Multiples vulnérabilités dans Citrix NetScaler ADC et Gateway

De multiples vulnérabilités ont été découvertes dans Citrix NetScaler ADC et Gateway. Certaines d'entre elles permettent à un attaquant de provoquer une exécution de code arbitraire à distance, un déni de service à distance et un contournement de la politique de sécurité. Citrix indique que les vulnérabilités CVE-2026-88771 et CVE-2026-88772 sont activement exploitées. L'éditeur indique que si les correctifs n'ont pas été installés, tous les équipements sont vulnérables dans leur configuration par défaut.

Official advisory ↗
CSIRT Italia · Italian · vulnerabilita-in-prodotti-citrix-netscaler-1Vulnerabilità in prodotti Citrix NetScaler

Nel dettaglio, la vulnerabilità identificata tramite la CVE-2026-88779, di tipo “Memory Overflow” e con CVSS 4.0 pari a 8.7, interessa Citrix NetScaler ADC e Citrix NetScaler Gateway. Tale vulnerabilità è riconducibile a una gestione non corretta della memoria e potrebbe consentire a un utente malintenzionato remoto non autenticato, in determinate condizioni, di causare l'indisponibilità del servizio dei sistemi interessati. Si evidenzia che risultano vulnerabili esclusivamente le istanze configurate come SAML Service Provider (SP) o SAML Identity Provider (IdP). Citrix ha inoltre osservato tentativi di sfruttamento verso i deployment NetScaler non mitigati, senza rilevare, allo stato, evidenze di compromissione dell’integrità dei dati.

Official advisory ↗
CSIRT Italia · Italian · vulnerabilita-in-prodotti-citrix-netscalerVulnerabilità in prodotti Citrix NetScaler

La vulnerabilità identificata tramite CVE-2026-88771, di tipo "Improper Input Validation", e con CVSS 4.0 pari a 9.5, interessa Citrix NetScaler ADC e Citrix NetScaler Gateway. Questa vulnerabilità è dovuta a un'errata convalida dell'input utente. Un utente malintenzionato remoto non autenticato potrebbe sfruttare tale vulnerabilità al fine di eseguire comandi arbitrari sui sistemi interessati. La vulnerabilità identificata tramite CVE-2026-88772, di tipo "Remote Code Execution", e con CVSS 4.0 pari a 9.5, interessa Citrix NetScaler ADC e Citrix NetScaler Gateway. Un utente malintenzionato potrebbe sfruttare tale vulnerabilità al fine di eseguire codice da remoto o compromettere la disponibilità del servizio sui sistemi interessati.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-035812シトリックス・システムズのnetscaler application delivery controller等の複数製品における以前の値から予測可能な正確な値に関する脆弱性

Citrix NetScaler ADCおよびCitrix NetScaler Gatewayには、前の値から予測可能な正確な値を扱う脆弱性があります。この問題は以下のバージョンに影響します。ADCでは14.1-73.37より前、13.1-64.23より前、14.1-73.37 FIPSより前、および13.1.37.279 FIPSおよびNDcPPより前のバージョンが対象です。Gatewayでは14.1-73.37より前および13.1-64.23より前のバージョンが影響を受けます。

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-6971Citrix 제품 보안 업데이트 권고

NetScaler ADC, NetScaler Gateway에서 발생하는 Predictable Exact Value from Previous Values 취약점(CVE-2026-88778) [1][9]

Official advisory ↗
NCSC-NL · Dutch · NCSC-2026-0394Kwetsbaarheden verholpen in NetScaler ADC en NetScaler Gateway

De kwetsbaarheden betreffen verschillende beveiligingsproblemen die onder meer kunnen leiden tot Remote Code Execution (RCE), HTTP Request Smuggling, het omzeilen van beleidsregels en Denial-of-Service. Drie kwetsbaarheden met kenmerk CVE-2026-88771, CVE-2026-88772 en CVE-2026-88773 zijn als kritiek aangemerkt. De kwetsbaarheid met kenmerk CVE-2026-88771 heeft een CVSS-score van 9,5 en betreft onvoldoende invoervalidatie. Een niet-geauthenticeerde kwaadwillende kan op afstand willekeurige commando's uitvoeren. Volgens Citrix zijn alle NetScaler ADC- en NetScaler Gateway-deployments getroffen en is geen aanvullende functionaliteit of specifieke configuratie voor misbruik vereist. De kwetsbaarheid met kenmerk CVE-2026-88772 heeft een CVSS-score van 9,5 en betreft een memory overflow die kan leiden tot RCE of Denial-of-Service. Misbruik is mogelijk wanneer DTLS is ingeschakeld. Citrix geeft aan dat DTLS standaard is ingeschakeld op een VPN virtual server. De kwetsbaarheid met kenmerk CVE-2026-88773 heeft een CVSS-score van 9,3 en betreft HTTP Request Smuggling. Voor misbruik moet HTTP-functionaliteit zijn ingeschakeld op NetScaler ADC of NetScaler Gateway. Authenticatie en gebruikersinteractie zijn niet vereist. De kwetsbaarheid met kenmerk CVE-2026-88774 heeft een CVSS-score van 7,0 en kan leiden tot het omzeilen van een feature policy door onjuist gebruik van HTTP URL-gebaseerde policy expressions. De kwetsbaarheid is alleen van toepassing wanneer dergelijke expressions zijn geconfigureerd. De kwetsbaarheid met kenmerk CVE-2026-88775 heeft een CVSS-score van 8,8 en betreft een memory overflow die kan leiden tot onvoorspelbaar gedrag of Denial-of-Service. De kwetsbaarheid is van toepassing op systemen die zijn geconfigureerd als Gateway, waaronder SSL VPN, ICA Proxy, CVPN en RDP Proxy, of als AAA virtual server. De kwetsbaarheid met kenmerk CVE-2026-88776 heeft een CVSS-score van 8,8 en betreft eveneens een memory overflow die kan leiden tot onvoorspelbaar gedrag of Denial-of-Service. Voor misbruik moet een load-balancing virtual server van het type Oracle zijn geconfigureerd. De kwetsbaarheid met kenmerk CVE-2026-88777 heeft een CVSS-score van 8,8 en betreft een memory overflow die kan leiden tot onvoorspelbaar gedrag of Denial-of-Service. De kwetsbaarheid vereist een LB-, CS- of CGNAT-LSN/NAT64-configuratie waarbij een non-HTTP Layer 7-protocol is ingeschakeld. De kwetsbaarheid met kenmerk CVE-2026-88778 heeft een CVSS-score van 8,8 en betreft voorspelbaarheid van TCP Initial Sequence Numbers (ISN). Voor misbruik moet TCP-functionaliteit zijn ingeschakeld op NetScaler ADC of NetScaler Gateway. Citrix meldt dat misbruik van de kwetsbaarheden met kenmerk CVE-2026-88771 en CVE-2026-88772 zijn waargenomen op NetScaler-systemen.

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Mitigation available
Affected
Fixed
No fixed version is explicitly recorded in the structured CVE data.
Action
On September 27, 2026, Cybersecurity and Infrastructure Security Agency (CISA) added CVE-2026-88771 and CVE-2026-88772 to their Known Exploited Vulnerabilities (KEV) Database. The Cyber Centre encourages users and administrators to review the provided web links and apply any necessary updates as they become available.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 27 Sept 2026 · Last source change 29 Sept 2026, 16:35 UTC · CWE-342 · Predictable Exact Value from Previous Values

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-09-28
European sourceENISA EUVD · EUVD-2026-87973
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Vendor guidanceAuthoritative vendor guidance changed: removed remediation: cyber.gc.ca/citrix-security-advisory-av26-965.
    Before
    remediation: cyber.gc.ca/citrix-security-advisory-av26-965 · vendor advisory: support.citrix.com/article?articleNumber=CTX697096
    After
    vendor advisory: support.citrix.com/article?articleNumber=CTX697096
    support.citrix.com ↗
  2. Vendor guidanceAuthoritative vendor guidance changed: removed remediation: cyber.gc.ca/al26-024-critical-vulnerabilities-affecting-citrix-netscaler-adc-netscaler-gateway-cve-2026-88771-cve-2026-88772.
    Before
    remediation: cyber.gc.ca/al26-024-critical-vulnerabilities-affecting-citrix-netscaler-adc-netscaler-gateway-cve-2026-88771-cve-2026-88772 · vendor advisory: support.citrix.com/article?articleNumber=CTX697096
    After
    vendor advisory: support.citrix.com/article?articleNumber=CTX697096
    support.citrix.com ↗
  3. Remediation statusRemediation status changed from Mitigation available to Awaiting fix.
    Before
    Mitigation available
    After
    Awaiting fix
    support.citrix.com ↗
  4. Remediation statusRemediation status changed from Awaiting fix to Mitigation available.
    Before
    Awaiting fix
    After
    Mitigation available
    Canadian Centre for Cyber Security ↗
  5. ENISA EUVD mappingEUVD-2026-87973 was added to the official ENISA EUVD mapping for this CVE.
    Before
    not recorded
    After
    {"euvdId":"EUVD-2026-87973"}
    ENISA EUVD ↗
  6. Remediation statusRemediation status changed from Awaiting fix to Mitigation available.
    Before
    Awaiting fix
    After
    Mitigation available
    Canadian Centre for Cyber Security ↗
  7. Vendor guidanceAuthoritative vendor guidance changed: removed remediation: cyber.gc.ca/al26-024-critical-vulnerabilities-affecting-citrix-netscaler-adc-netscaler-gateway-cve-2026-88771-cve-2026-88772.
    Before
    remediation: cyber.gc.ca/al26-024-critical-vulnerabilities-affecting-citrix-netscaler-adc-netscaler-gateway-cve-2026-88771-cve-2026-88772 · vendor advisory: support.citrix.com/article?articleNumber=CTX697096
    After
    vendor advisory: support.citrix.com/article?articleNumber=CTX697096
    support.citrix.com ↗
  8. Vendor guidanceAuthoritative vendor guidance changed: added vendor advisory: support.citrix.com/article?articleNumber=CTX697096; removed remediation: cyber.gc.ca/al26-024-critical-vulnerabilities-affecting-citrix-netscaler-adc-netscaler-gateway-cve-2026-88771-cve-2026-88772.
    Before
    remediation: cyber.gc.ca/al26-024-critical-vulnerabilities-affecting-citrix-netscaler-adc-netscaler-gateway-cve-2026-88771-cve-2026-88772
    After
    vendor advisory: support.citrix.com/article?articleNumber=CTX697096
    support.citrix.com ↗
  9. Remediation statusRemediation status changed from Mitigation available to Awaiting fix.
    Before
    Mitigation available
    After
    Awaiting fix
    support.citrix.com ↗
  10. Vendor guidanceAuthoritative vendor guidance changed: removed remediation: cyber.gc.ca/al26-024-critical-vulnerabilities-affecting-citrix-netscaler-adc-netscaler-gateway-cve-2026-88771-cve-2026-88772.
    Before
    remediation: cyber.gc.ca/al26-024-critical-vulnerabilities-affecting-citrix-netscaler-adc-netscaler-gateway-cve-2026-88771-cve-2026-88772
    After
    no authoritative guidance recorded
    CNA ↗
  11. Remediation statusRemediation status changed from Mitigation available to Awaiting fix.
    Before
    Mitigation available
    After
    Awaiting fix
    CNA ↗
  12. Catalogue recordCVE added to the BlackTree catalogue.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Remediation guidance recorded
ENISA EUVD · EUVD-2026-87973↗Canadian Centre for Cyber Security remediation guidance↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-88778 · cve.blacktree.nl