Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow Vulnerability

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.

CheckOps priority index

9.8/10 Patch within 24 h

Severity9.4

Probability10.0

Exploitation5/5

Severity = CVSS. Probability = EPSS (FIRST). Exploitation = public signals: KEV, EUVD, ransomware, EPSS above 10 %, no account required.

EPSS · today 100.00% higher than 100.00% of CVEs

CVSS 3.1 9.4 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:

Exploited for 1,112 days 18 Oct 2023

CISA due date 08 Nov 2023 for US federal agencies

Exploitation probability EPSS · FIRST

EPSS probability (%)Percentile among all CVEs

Exploitation signals 5 / 5

KEV catalog (CISA)18 Oct 2023
Exploited in EUVD (ENISA)18 Oct 2023
Used by ransomwareyes
EPSS above 10 %100.00%
No account, over the networkyes

What to do

Fix

Apply the vendor’s fix as soon as it is available.

CISA guidance: Apply mitigations and kill all active and persistent sessions per vendor instructions [https://www.netscaler.com/blog/news/cve-2023-4966-critical-security-update-now-available-for-netscaler-adc-and-netscaler-gateway/] OR discontinue use of the product if mitigations are unavailable.

Meanwhile

Take the service off the internet or restrict access to it, watch the logs and look for signs of compromise.

Manufacturers (CRA)

Exploited vulnerability in your product: early warning to ENISA within 24 h, then notification within 72 h (Article 14 of the Cyber Resilience Act). The CRA explained

Affected products

NetScaler GatewayNetScaler ADCNetScaler ADC and NetScaler Gateway

Affected versions

13.1 <49.15
12.1-FIPS <55.300
13.0 <92.19
13.1-FIPS <37.164
14.1 <8.50
12.1-NDcPP <55.300

Weaknesses (CWE)

CWE-119

Open source packages OSV

Affected libraries according to OSV, with fixed versions.

Timeline

10 Oct 2023
Published
18 Oct 2023
Exploitation reported (ENISA)
18 Oct 2023
Added to the KEV catalog
08 Nov 2023
CISA remediation due date
26 Sept 2026
EPSS peak: 100.00%

References

Other exploited vulnerabilities from the same vendor

CVE-2026-88779Citrix NetScaler Improper Restriction of Operations within the Bounds of a Memory Buffer Vulnerability
6.2 · Actively exploited
CVE-2026-88772Citrix NetScaler Improper Restriction of Operations within the Bounds of a Memory Buffer Vulnerability
8.5 · Actively exploited
CVE-2026-88771Citrix NetScaler Improper Input Validation Vulnerability
8.7 · Actively exploited
CVE-2026-19490Citrix NetScaler Authentication Bypass Using an Alternate Path or Channel Vulnerability
7.1 · Actively exploited
CVE-2026-8452Citrix NetScaler ADC and NetScaler Gateway Improper Restriction of Operations within the Bounds of a Memory Buffer Vulnerability
5.4 · Actively exploited
CVE-2026-3055Citrix NetScaler Out-of-Bounds Read Vulnerability
8.9 · Background exploitation