CVE-2023-6549: in the CISA KEV catalogue

Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow Vulnerability. CISA added CVE-2023-6549 to the Known Exploited Vulnerabilities catalogue on 2024-01-17 with a default due date of 2024-02-07. Known ransomware campaign use: Unknown. Forensic triage flag: No.

Citrix NetScaler ADC and NetScaler Gateway contain a buffer overflow vulnerability that allows for a denial-of-service when configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server. (CISA description)

Vendor / product: Citrix NetScaler ADC and NetScaler Gateway
CWE: CWE-119
CISA required action: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
EPSS: 58%, percentile 99 (scored 2026-11-03)

EPSS puts about 58 in 100 odds (58%) on exploitation activity being observed in the next 30 days. Its score is higher than or equal to that of 99% of scored CVEs. This is a model estimate about exploitation anywhere, not about your environment.

Vendor and reference links (from CISA)

Your own deadline under CISA BOD 26-04 depends on exposure, automatability and technical impact: work it out with the BOD 26-04 calculator.

Data dates. CISA KEV catalogue version 2026.11.03, released 2026-11-03, 1,767 entries (checked 2026-11-03). EPSS model v2026.06.15, scored 2026-11-03, 399,388 CVEs. Sources: CISA and FIRST (EPSS by FIRST; scores generated by Empirical Security). Copied to our own database and refreshed automatically; if a refresh fails, the previous copy keeps serving with its own date.

Frequently asked questions

Is CVE-2023-6549 in the CISA KEV catalogue?

Yes. CISA added CVE-2023-6549 (Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow Vulnerability) to the Known Exploited Vulnerabilities catalogue on 2024-01-17. CISA's default due date for it is 2024-02-07.

Is CVE-2023-6549 used in ransomware attacks?

CISA marks known ransomware campaign use as Unknown for CVE-2023-6549. That means CISA lacks confirmation, not that ransomware groups do not use it.

What should I do about CVE-2023-6549?

CISA's required action: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

Sources

CISA, Known Exploited Vulnerabilities Catalog (accessed 2026-11-03)
FIRST, Exploit Prediction Scoring System (EPSS) (EPSS by FIRST; scores generated by Empirical Security)
NVD record for CVE-2023-6549