CVE-2023-6549: Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow Vulnerability
Actively exploited. At least one CVE in this advisory is listed in the CISA Known Exploited Vulnerabilities catalog — exploitation has been observed in the wild. Treat remediation as urgent.
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.
CSIRTS triage
- What
- A buffer overflow vulnerability allows for denial-of-service when configured as a Gateway or AAA virtual server.
- Who is affected
- Deployments of Citrix NetScaler ADC and NetScaler Gateway.
- Urgency
- Immediate action is required due to active exploitation and critical severity.
- Action
- Update to the latest version as recommended by Citrix.
AI-assisted analysis generated from the source advisory — verify against the original.
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Details
Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2023-6549
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Exploitation confirmedCVE-2023-6549Already exploited in the wild (CISA KEV) — the prediction phase is over. Patch now. Riskier than 99% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2023-6549 | coverage & exploitation status | NVD · CVE.org |
Recent advisories for Citrix NetScaler ADC
A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.
- high[UPDATE] [high] Citrix Systems NetScaler ADC and Gateway: Multiple vulnerabilitiescert-bund · 2026-07-02
- unknownNCSC-2026-0216 [1.00] [M/H] Vulnerabilities fixed in Citrix Netscaler ADC and Netscaler Gatewayncsc-nl · 2026-06-30
- unknown2026-003: Multiple Vulnerabilities in Citrix NetScaler and Citrix ADCcert-eu · 2026-03-23
- unknownexploitedVulnerability in Citrix NetScaler ADC and NetScaler Gateway (August 26, 2025)cert-fr-alerte · 2025-08-26
- criticalexploitedCVE-2025-5777: Citrix NetScaler ADC and Gateway Out-of-Bounds Read Vulnerabilitycisa-kev · 2025-07-10
- unknownMultiple vulnerabilities in Citrix NetScaler ADC and NetScaler Gateway (July 1, 2025)cert-fr-alerte · 2025-07-01
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