CVE-2023-4966: Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow Vulnerability
Also known as Citrix Bleed
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on , 8 days after the CVE record was published.
- How likely is exploitation in the next 30 days?
- 100%
EPSS score, percentile 100 of all scored records
- How severe?
- 9.4 Critical
CVSS v3.1 base score, given by the CNA
- What should I do?
CISA deadline . Apply mitigations and kill all active and persistent sessions per vendor instructions … Full text
The CVE record links no vendor advisory, patch or mitigation.
- Which versions are affected?
Affected
- from 14.1 to before 8.50
- from 13.1 to before 49.15
- from 13.0 to before 92.19
- from 13.1-FIPS to before 37.164
- from 12.1-FIPS to before 55.300
- from 12.1-NDcPP to before 55.300
and 3 more in the table below
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
What to do
Required action, set by CISA
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.
CISA due date for this action: .
Advisories and patches
The CVE record links no vendor advisory, patch or mitigation.
Linked from CISA's catalog entry
- https://www.netscaler.com/blog/news/cve-2023-4966-critical-security-update-now-available-for-netscaler-adc-and-netscaler-gateway/
- https://support.citrix.com/article/CTX579459/netscaler-adc-and-netscaler-gateway-security-bulletin-for-cve20234966-and-cve20234967
- https://nvd.nist.gov/vuln/detail/CVE-2023-4966
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | from 14.1 to before 8.50 |
| Affected | from 13.1 to before 49.15 |
| Affected | from 13.0 to before 92.19 |
| Affected | from 13.1-FIPS to before 37.164 |
| Affected | from 12.1-FIPS to before 55.300 |
| Affected | from 12.1-NDcPP to before 55.300 |
Versions not listed are: unaffected.
| Status | Versions |
|---|---|
| Affected | from 14.1 to before 8.50 |
| Affected | from 13.1 to before 49.15 |
| Affected | from 13.0 to before 92.19 |
Versions not listed are: unaffected.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
About this vulnerability
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: CISA's KEV catalog, as of .
- CISA added CVE-2023-4966 to its Known Exploited Vulnerabilities (KEV) catalog on 18 Oct 2023.
- It is widely known as Citrix Bleed, a common name that is not used in the CVE record or in CISA's catalog.
- CISA marks it as known to be used in ransomware campaigns.
- The due date CISA sets for the required action is 8 Nov 2023.
- The CVE record was published on 10 Oct 2023, 8 days before it was added to KEV.
- The CVE record carries a CVSS v3.1 base score of 9.4 (Critical), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 100% (percentile 100), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation active, automatable yes, technical impact total.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of . About the data.
Description
Unauthenticated sensitive information disclosure
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.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
Weakness
- CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| CVE record published | |
| Added to CISA KEV | |
| CISA due date for the required action | |
| CVE record last updated |
References
More exploited Citrix vulnerabilities
- CVE-2026-88779: Citrix NetScaler Improper Restriction of Operations within the Bounds of a Memory Buffer Vulnerability
- CVE-2026-88771: Citrix NetScaler Improper Input Validation Vulnerability
- CVE-2026-88772: Citrix NetScaler Improper Restriction of Operations within the Bounds of a Memory Buffer Vulnerability
- CVE-2026-19490: Citrix NetScaler Authentication Bypass Using an Alternate Path or Channel Vulnerability
- CVE-2026-8452: Citrix NetScaler ADC and NetScaler Gateway Improper Restriction of Operations within the Bounds of a Memory Buffer Vulnerability
- CVE-2026-3055: Citrix NetScaler Out-of-Bounds Read Vulnerability