Exploited Ransomware

CVE-2023-4966

Citrix NetScaler ADC / Gateway · Load balancers and access gateways (ADC)

Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow Vulnerability

At a glance

Exploited. Added to CISA’s catalog of exploited vulnerabilities on October 18, 2023.

Used in ransomware attacks, according to CISA.

Affected product: Citrix NetScaler ADC / Gateway (category Load balancers and access gateways (ADC), indicative classification). Name in CISA’s catalog: Citrix NetScaler ADC and NetScaler Gateway.

What should I do?

Apply the patches or mitigations from Citrix; if none are available, stop using the product.

Deadline set by CISA for US federal agencies: 21 days (due November 8, 2023). It only binds those agencies, but it is a useful measure of urgency.

Citrix security advisories page (general page, not the advisory for this vulnerability)
The vendor’s specific advisory is listed in the NVD references: CVE-2023-4966 on the NVD website.

Original text of the required action (CISA)

Apply mitigations and kill all active and persistent sessions per vendor instructions [[lien retiré] OR discontinue use of the product if mitigations are unavailable.

Timeline

October 10, 2023 Vulnerability published Publication date (NVD)
October 18, 2023 Exploitation confirmed Added to CISA’s KEV catalog
November 8, 2023 CISA deadline Remediation deadline set for US federal agencies

The facts, with their sources

Exploitation confirmed: Yes, on October 18, 2023 Date added to the catalog of exploited vulnerabilities. Exploitation itself may have started earlier. Source: KEV catalog, collected September 29, 2026 at 14:57 UTC
Ransomware: Known use Source: KEV catalog, collected September 29, 2026 at 14:57 UTC
Hunt for compromise: Not requested by CISA Source: KEV catalog, collected September 29, 2026 at 14:57 UTC
CISA required action: Apply the patches or mitigations from Citrix; if none are available, stop using the product. Rewritten by this site from CISA’s original text. Source: KEV catalog, collected September 29, 2026 at 14:57 UTC
CISA deadline: November 8, 2023, 21 days Set for US federal agencies: a measure of urgency, not an obligation elsewhere. Source: KEV catalog, collected September 29, 2026 at 14:57 UTC
Vulnerability published: October 10, 2023 Source: National Vulnerability Database (NVD), collected September 29, 2026 at 15:00 UTC
Product according to CISA: Citrix NetScaler ADC and NetScaler Gateway Filed by this site under “Load balancers and access gateways (ADC)” (indicative classification). Source: KEV catalog, collected September 29, 2026 at 14:57 UTC
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Technical detail of the score: attack vector, complexity, impact. Source: National Vulnerability Database (NVD), collected September 29, 2026 at 15:00 UTC

Severity and activity

7.5 / 10 CVSS severity: high

Score from the NVD. Collected Sep 29, 2026.

— Probability of exploitation in the next 30 days (EPSS)

FIRST’s EPSS model. Since exploitation is already confirmed, this figure is mostly useful to compare activity. Collected Sep 29, 2026.

Description

Sensitive information disclosure in NetScaler ADC and NetScaler Gateway when configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server.

Citrix NetScaler ADC and NetScaler Gateway contain a buffer overflow vulnerability that allows for sensitive information disclosure when configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server.

Summary from CISA (KEV catalog).

CERT-FR advisories

No advisory among the latest CERT-FR publications this site follows. That does not mean there are none.

Information reused under the Open Licence 2.0 (Etalab); the date of last update is shown for each advisory. This site is neither affiliated with nor endorsed by ANSSI.

Sources for this page

CISA KEV catalog: exploitation, date added, required action, deadline, ransomware.
NVD (NIST): CVSS severity, publication date, description, vendor references.
EPSS (FIRST): probability of exploitation.
CERT-FR: advisories and alerts (in French).
Brand and category: indicative classification by this site (method).