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PatchSiren cyber security CVE debrief

CVE-2023-4966 Citrix CVE debrief

CVE-2023-4966 is a Citrix NetScaler ADC and NetScaler Gateway buffer overflow vulnerability that was publicly recorded on 2023-10-18 and added to CISA’s Known Exploited Vulnerabilities catalog the same day. CISA marks it as known exploited, with known ransomware campaign use, and sets a remediation due date of 2023-11-08. Organizations running affected NetScaler deployments should treat this as an urgent exposure and follow vendor-directed mitigations immediately.

Vendor
Citrix
Product
NetScaler ADC and NetScaler Gateway
CVSS
CRITICAL 9.4
CISA KEV
Listed
Original CVE published
2023-10-18
Original CVE updated
2026-09-27
Advisory published
2026-09-27
Advisory updated
2026-09-27

Who should care

Security and infrastructure teams responsible for Citrix NetScaler ADC or NetScaler Gateway, especially internet-facing environments; incident response teams; and defenders validating whether any systems still rely on vulnerable or unmitigated deployments.

Technical summary

The supplied source corpus identifies CVE-2023-4966 as a buffer overflow vulnerability in Citrix NetScaler ADC and NetScaler Gateway. The KEV entry indicates active exploitation in the wild and references vendor mitigations, but the supplied corpus does not include deeper technical impact details or a CVSS score.

Defensive priority

Critical

Recommended defensive actions

  • Apply the vendor-referenced mitigations immediately for all affected Citrix NetScaler ADC and NetScaler Gateway systems.
  • Kill active and persistent sessions per vendor instructions if your environment is affected.
  • If mitigations are not available or cannot be applied promptly, discontinue use of the product as directed in the CISA KEV notes.
  • Validate exposure across all internet-facing and internally reachable NetScaler instances.
  • Review incident response telemetry for signs of compromise because CISA classifies this issue as known exploited and notes known ransomware campaign use.

Evidence notes

The supplied corpus shows: (1) the CVE title/description identifying a Citrix NetScaler ADC and NetScaler Gateway buffer overflow vulnerability; (2) CISA KEV metadata marking the issue as known exploited, with known ransomware campaign use, dateAdded 2023-10-18, and dueDate 2023-11-08; and (3) the required action to apply mitigations and kill active/persistent sessions per vendor instructions, or discontinue use if mitigations are unavailable. No CVSS score or additional exploit mechanics were provided in the supplied corpus.

Sources and references

Verified primary and authoritative sources

  • CVE-2023-4966 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2023-4966

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2023-4966 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2023-4966

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

  • CISA Known Exploited Vulnerabilities catalog

    Publisher, destination, and source semantics verified

    URL: https://www.cisa.gov/known-exploited-vulnerabilities-catalog

    Cybersecurity and Infrastructure Security Agency - Official CISA catalog of vulnerabilities known to be exploited in the wild.

Supplemental references

  • Source item URL

    Unverified legacy reference

    URL: https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json

    cisa_kev

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.