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Full vulnerability report · 2024
CVE-2023-6549High confidence

Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow Vulnerability

Citrix · NetScaler ADC and NetScaler Gateway

8.2HighCVSS 3.1
Recommended action
Protect now

CISA confirms exploitation in the wild and lists 2024-02-07 as the remediation due date.

Fix not verified
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:Critical, raised one band.upgradedsince 17 Jan 2024

Evidence used

  • CISA confirms exploitation in the wild.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 57.63% for the current model date.

Compensating controls

  • Restrict the affected network interface to trusted sources where business-safe.
  • Increase monitoring for the attack path and post-exploitation behaviour described in the report.

Verification

  1. Confirm that the asset runs Citrix NetScaler ADC and NetScaler Gateway and falls inside the recorded affected range.
  2. Recheck the vendor advisory before scheduling a change because no verified fixed version is currently retained.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 3 daysRemediation target: Within 90 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2023-58779

CISA KEV mirrored by ENISA

Improper Restriction of Operations within the Bounds of a Memory Buffer in NetScaler ADC and NetScaler Gateway allows Unauthenticated Denial of Service and Out-Of-Bounds Memory Read

EUVD state
Present in the current official mapping
Known exploitation
Recorded by ENISA since 17 Jan 2024. Evidence sources: cisa_kev.
ENISA score
8.2 · CVSS 3.1
Advisory evidence
1 linked advisory record
Recommended actionProtect now

CISA confirms exploitation in the wild and lists 2024-02-07 as the remediation due date.

Fix not verified
01

What, why and how

Citrix NetScaler ADC and NetScaler Gateway contain a buffer overflow vulnerability that allows for a denial-of-service when configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server.

What

Citrix NetScaler ADC and NetScaler Gateway contain a buffer overflow vulnerability that allows for a denial-of-service when configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server.

Why

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

Citrix NetScaler ADC and NetScaler Gateway contain a buffer overflow vulnerability that allows for a denial-of-service when configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server.

Why

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Confirmed in the wild

CISA added this CVE to its Known Exploited Vulnerabilities catalogue on 2024-01-17.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Improper Restriction of Operations within the Bounds of a Memory Buffer → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-119 ↗

CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer. The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.ILowIntegrity impact: A successful attack can cause a limited loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-119CISA KEV
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2023-58779Known-exploited evidence recorded

Improper Restriction of Operations within the Bounds of a Memory Buffer in NetScaler ADC and NetScaler Gateway allows Unauthenticated Denial of Service and Out-Of-Bounds Memory Read

Official EUVD record ↗
BSI · German · WID-SEC-2024-0133Citrix Systems Produkte: Mehrere Schwachstellen

Ein entfernter, authentisierter Angreifer kann mehrere Schwachstellen in Citrix Systems ADC und Citrix Systems Citrix Gateway ausnutzen, um beliebigen Programmcode auszuführen oder einen Denial of Service zu verursachen.

Official advisory ↗
Canadian Centre for Cyber Security · English · AV24-030Citrix security advisory (AV24-030)

On January 16, 2024, Citrix published security advisories to address vulnerabilities in multiple products. Included were updates for the following: Citrix has indicated that CVE-2023-6548 and CVE-2023-6549 have been actively exploited.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20240124Security Bulletin 24 Jan 2024

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 24 Jan 2024, published on 24 January 2024. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0039Multiples vulnérabilités dans les produits Citrix

De multiples vulnérabilités ont été découvertes dans les produits Citrix. Elles permettent à un attaquant de provoquer une exécution de code arbitraire à distance, un déni de service à distance et une injection de code indirecte à distance (XSS).

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2023-025480シトリックス・システムズの netscaler application delivery controller および netscaler gateway におけるバッファエラーの脆弱性

シトリックス・システムズの netscaler application delivery controller および netscaler gateway には、バッファエラーの脆弱性が存在します。

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-6079Citrix 제품 보안 업데이트 권고

NetScaler ADC 및 NetScaler Gateway에서 발생하는 서비스 거부(Dos) 취약점(CVE-2023-6549) [2]

Official advisory ↗
KISA KrCERT/CC · Korean · KNVD-6077美 CISA 발표 주요 Exploit 정보공유(Update. 2024-01-17)

Citrix NetScaler ADC and NetScaler Gateway contain a buffer overflow vulnerability that allows for a denial-of-service when configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server.

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Fix not verified
Affected
NetScaler ADC: 14.1 < 12.35, 13.1 < 51.15, 13.0 < 92.21, 13.1-FIPS < 37.176, 12.1-FIPS < 55.302, 12.1-NDcPP < 55.302
Fixed
No fixed version is explicitly recorded in the structured CVE data.
Action
No verified patch reference is present in the current structured sources. Check the vendor advisory before making a change.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 17 Jan 2024 · Last source change 21 Oct 2025, 23:05 UTC · CWE-119 · Improper Restriction of Operations within the Bounds of a Memory Buffer

CVE recordCVE.org · 5.1
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2023-58779
Product sourceCISA KEV
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Vendor guidanceAuthoritative vendor guidance changed: removed remediation: cyber.gc.ca/citrix-security-advisory-av24-030.
    Before
    remediation: cyber.gc.ca/citrix-security-advisory-av24-030 · vendor advisory: support.citrix.com/netscaler-adc-and-netscaler-gateway-security-bulletin-for-cve20236548-and-cve20236549
    After
    vendor advisory: support.citrix.com/netscaler-adc-and-netscaler-gateway-security-bulletin-for-cve20236548-and-cve20236549
    support.citrix.com ↗
  2. Remediation statusRemediation status changed from Mitigation available to Awaiting fix.
    Before
    Mitigation available
    After
    Awaiting fix
    support.citrix.com ↗
  3. Affected versionsThe structured affected or fixed version information changed.
    Before
    14.1 < 12.35; 13.1 < 51.15; 13.0 < 92.21; 13.1-FIPS < 37.176; 12.1-FIPS < 55.302; 12.1-NDcPP < 55.302 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    NetScaler ADC: 14.1 < 12.35, 13.1 < 51.15, 13.0 < 92.21, 13.1-FIPS < 37.176, 12.1-FIPS < 55.302, 12.1-NDcPP < 55.302 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    CNA ↗
  4. Remediation statusRemediation status changed from Awaiting fix to Mitigation available.
    Before
    Awaiting fix
    After
    Mitigation available
    Canadian Centre for Cyber Security ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Added to CISA KEV
ENISA EUVD · EUVD-2023-58779↗CISA KEV record↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2023-6549 · cve.blacktree.nl