What is the CVSS score of CVE-2023-4966?

CVE-2023-4966 has a CVSS 3.1 base score of 7.5 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. EPSS exploitation probability: 94.3%.

Is there a public PoC exploit available for CVE-2023-4966?

Yes, a public proof-of-concept exploit is available for CVE-2023-4966. Prioritise patching immediately. EPSS: 94.3%.

How to fix or mitigate CVE-2023-4966?

Within 24 hours: inventory all Citrix NetScaler ADC and Gateway instances and prioritize those configured as Gateway or AAA virtual servers; implement strict firewall rules restricting network access to NetScaler appliances from external sources; establish baseline monitoring and alerting for exploitation attempts. Within 7 days: deploy Web Application Firewall rules to block known Citrix Bleed exploitation patterns; enable comprehensive session and authentication logging with real-time review for anomalous token usage; implement session re-validation checks on critical applications. Within 30 days: prepare migration to a patched Citrix NetScaler version when released by vendor; conduct 90-day retroactive forensic analysis of authentication logs for indicators of compromise; architect network isolation to separate critical business applications from affected NetScaler instances pending permanent remediation.

NetScaler ADC CVE-2023-4966

HIGH

Buffer Overflow (CWE-119)

2023-10-10 secure@citrix.com

Buffer Overflow Information Disclosure Citrix Netscaler Application Delivery Controller Netscaler Gateway

7.5

CVSS 3.1 · NVD

View

Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

Access

Identify internet-facing NetScaler Gateway/AAA endpoint
Delivery

Send crafted HTTP request to leak memory
Exploit

Extract valid session token from buffer over-read
Execution

Replay token to hijack authenticated session
Impact

Bypass MFA and access internal resources

Vulnerability Assessment

Weakness	CWE CWE-119 OWASP Top 10:2025 A06:2021 - Vulnerable and Outdated Components ASVS 5.0 V14 - Configuration Dependency management, component inventory MITRE ATT&CK 2 techniques across 2 tactics: Execution, Privilege Escalation The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Exploitation Conditions	Exploitable only when the NetScaler ADC or Gateway appliance is configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, or RDP Proxy) or as an AAA virtual server - appliances not serving these roles are not affected, which is the primary limiting factor. Beyond that role requirement there are no special conditions: exploitation is remote and unauthenticated (AV:N/AC:L/PR:N/UI:N) with no user interaction, and the vulnerable Gateway/AAA endpoints are typically internet-facing by design. Effectiveness is greatest against sessions that have already authenticated, since the leaked memory must contain a live session token to be useful for hijacking.
Impact	This is a top-tier real-world priority, with multiple signals aligned: the CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N) indicates trivial remote unauthenticated exploitation, EPSS is 94.35% at the 100th percentile, the vulnerability is in CISA KEV as confirmed actively exploited, and public POC (Citrix Bleed) exists. The base CVSS of 7.5 (confidentiality-only, C:H/I:N/A:N) understates practical impact because leaked session tokens enable full authenticated session hijacking that defeats MFA - a downstream integrity/access consequence not captured by the base score. One minor note: the CWE is mapped to CWE-119 (memory buffer bounds) while the practical effect is information disclosure via over-read (closer to CWE-125); this does not change the risk conclusion. No signals conflict - every indicator points to urgent remediation.
Exploit ScenarioDerived	A remote attacker sends a specially crafted HTTP request to the NetScaler Gateway or AAA virtual server endpoint, causing the appliance to return adjacent memory contents containing a valid user session token. Using the publicly available Citrix Bleed POC, the attacker replays this token to hijack an authenticated session, bypassing password and MFA controls, and then pivots into internal resources. No authentication or user interaction is required, making mass automated exploitation trivial.

Act Now Prioritize within 24-48h. Why: HIGH severity + EPSS > 10%.

Exploited in the wild (CISA KEV) No patch listed yet 94.3% exploitation probability (EPSS)

Get an e-mail when this CVE is exploited, patched or re-scored. Free account.

Alert me

AnalysisAIv2 – Jul 31, 2026

Sensitive information disclosure in Citrix NetScaler ADC and NetScaler Gateway - widely known as 'Citrix Bleed' - allows remote unauthenticated attackers to leak memory contents, including valid session tokens, when the appliance is configured as a Gateway or AAA virtual server. This is confirmed actively exploited (CISA KEV) with publicly available exploit code and an EPSS score of 94.35% (100th percentile), and leaked tokens enable session hijacking that bypasses multifactor authentication.

Earlier versions of this analysis (1)

v1 Mar 26, 2026 - 11:19 CVSS 9.4

A buffer over-read vulnerability in NetScaler ADC and Gateway (CitrixBleed) leaks session tokens and other sensitive data from device memory, enabling attackers to hijack authenticated sessions without credentials.

RemediationAI

Vendor-released patch: upgrade to NetScaler ADC/Gateway 14.1-8.50, 13.1-49.15, 13.0-92.19, 13.1-FIPS 13.1-37.164, 12.1-FIPS 12.1-55.300, or 12.1-NDcPP 12.1-55.300 or later, per Citrix advisory https://support.citrix.com/article/CTX579459. End-of-life 12.1 and 13.0 builds must be migrated to a supported, patched branch. Critically, patching alone is insufficient because leaked tokens persist: after upgrading, terminate all active and persistent sessions by running 'kill icaconnection -all', 'kill rdp connection -all', 'kill pcoipConnection -all', 'kill aaa session -all', and 'clear lb persistentSessions' to invalidate any session tokens an attacker may have already harvested. If immediate patching is impossible, restrict network access to the Gateway/AAA virtual server endpoints and monitor for anomalous authenticated sessions; note that restricting access may disrupt legitimate remote users, which is the trade-off of this compensating control.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

NetScaler ADC (formerly Citrix ADC) and NetScaler Gateway are network appliances providing application delivery, load balancing, and secure remote-access VPN/ICA proxy services. The flaw is rooted in a buffer over-read (CWE-119, improper restriction of operations within memory buffer bounds); a crafted HTTP request to the Gateway/AAA endpoint causes the appliance to return more data from an adjacent memory buffer than intended. Affected products per CPE include citrix:netscaler_application_delivery_controller (in standard, FIPS, and NDcPP builds) and citrix:netscaler_gateway. Because the over-read returns residual heap memory, it frequently discloses previously-authenticated user session tokens that can be replayed.

Know when Netscaler Gateway gets its next vulnerability

Watch products and get an email when something new is published
Check this CVE against your own stack and servers
Exploit and PoC references, threat intelligence from 22 sources

Continue with Google Continue with GitHub

No credit card · 7-day full trial

Severity by source

NVD PRIMARY 7.5 HIGH

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

vuln.today AI 7.5 HIGH

Remote unauthenticated buffer over-read needing no user interaction leaks memory (C:H); no direct integrity or availability impact at the base level, so I:N/A:N.

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

4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from NVD.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Lifecycle Timeline

Analysis Updated

Jul 31, 2026 - 04:28 vuln.today

v2 - CVSS changed

Severity Changed

Jul 31, 2026 - 04:22 NVD

CRITICAL HIGH

CVSS changed

Jul 31, 2026 - 04:22 NVD

9.4 (CRITICAL) 7.5 (HIGH)

Added to CISA KEV

Oct 24, 2025 - 13:42 cisa

CISA KEV

CVE Published

Oct 10, 2023 - 14:15 nvd

CRITICAL 9.4

DescriptionNVD

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.

Executive ViewAI

Why It Matters

Citrix NetScaler ADC and Gateway appliances face immediate risk from a critical memory disclosure vulnerability ('Citrix Bleed') that allows unauthenticated remote attackers to extract valid session tokens, enabling account takeover and multi-factor authentication bypass. The vulnerability is confirmed actively exploited (CISA KEV) with no vendor patch currently available, creating an urgent remediation priority for any organization operating these critical access control appliances. Compromised credentials provide attackers with direct access to enterprise applications and sensitive infrastructure.

Business Impact: Severe

Compensating Controls

No vendor-released patch identified at time of analysis. Interim mitigations: implement perimeter network segmentation and firewall rules restricting unauthenticated access to NetScaler instances; deploy Web Application Firewall rules to block memory disclosure exploitation patterns; enable verbose session and authentication logging with behavioral anomaly detection for stolen token usage; implement geographic IP restrictions and real-time session anomaly detection to identify session hijacking; physically or logically isolate the most critical business applications from affected NetScaler instances until patched version is available.

Threat Intelligence Overview

Threat Score

9.3/10

Composite threat intelligence

EPSS Score

94.3%

Top 0% exploitable

Prevalence

High

widely deployed enterprise remote-access appliance in large organizations

Threat Intel

1 sources

Exploit

POC

Public exploit code exists

Data Quality

5 sources

Confidence: Medium

Citrix

NVD

CVE.org

CISA KEV

EPSS POC (2) THREAT

VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity HIGH

CISA KEV Yes

Public POC Yes

EPSS 94.3%

Patch available No

Active threat Yes

Deciding rule

HIGH severity + EPSS > 10%

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Immediate

Exploitation· derived

Active

System Exposure· derived

Open

Automatable· derived

Yes

Human Impact

Very High

Priority Score

212

Low Medium High Critical

KEV: +50

EPSS: +94

CVSS: +38

PoC: +20

Weaponized: 0

Threat intel: +10

Gov advisory: 0

Attack Technique

Buffer Overflow HIGH

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.