Unauthenticated sensitive information disclosure

cisa required action 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.

1. 2023-10-10 CISA SSVC: exploitation active
2. 2023-10-10 Published
3. 2023-10-18 Added to CISA KEV
4. 2023-10-25 First public exploit (Metasploit auxiliary/scanner/http/citrix_bleed_cve_2023_4966)
5. 2023-11-08 CISA patch deadline

Added

3 y ago (2023-10-18)

Patch by

2023-11-08 (3 y ago)

Ransomware

Known to be used in ransomware campaigns

Required action

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.

Vendor, product

Citrix, NetScaler ADC and NetScaler Gateway

CISA name

Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow Vulnerability

Groups reported to have exploited it in intrusions.

• LockBit ransomware gang
• Medusa ransomware gang
• BlackCat ransomware gang
• INC Ransom ransomware gang
• Storm-0501 affiliate

reported by doublepulsar.combleepingcomputer.comtherecord.mediasecureworks.commicrosoft.com

Ransomware Vulnerability Matrix by BushidoUK (github.com/BushidoUK/Ransomware-Vulnerability-Matrix), reformatted per CVE. CC BY 4.0

How it is exploited and what it leads to, in MITRE ATT&CK terms.

• T1574 Hijack Execution Flow exploitation
• T1005 Data from Local System primary impact
• T1134.001 Token Impersonation/Theft secondary impact

kev release 2025-07-28, att&ck v16.1. KEV to ATT&CK mappings by the MITRE Center for Threat-Informed Defense (Mappings Explorer, Apache-2.0). © 2026 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation. Terms of use

Exploitation

Active, exploited in the wild

Automatable

yes

Technical impact

total

Assessed

3 y ago (2023-10-10)

100.00% chance of exploitation in the next 30 days, higher than 99.9% of all scored CVEs (FIRST EPSS, 2026-11-08).

• Metasploit auxiliary/scanner/http/citrix_bleed_cve_2023_4966 Citrix ADC (NetScaler) Bleed Scanner metasploit auxiliary, normal rank, 2023-10-25
• Nuclei template Citrix Bleed - Leaking Session Tokens nuclei detection template

• Citrix NetScaler ADC
• Citrix NetScaler Gateway

Weakness

• CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer

Technology feeds

• Citrix rss critical rss

• support.citrix.com /article/CTX579459

  vendor-advisory

• packetstormsecurity.com /files/175323/Citrix-Bleed-Session-Token-Leakage-Proof-Of-Concept.html

  third-party-advisory, vdb-entry

• cisa.gov /known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-4966

  government-resource, us-government-resource

• CVE List CVE-2023-4966
• NVD CVE-2023-4966

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.