What is the CVSS score of CVE-2025-6543?

CVE-2025-6543 has a CVSS 3.1 base score of 9.8 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 2.0%.

Which versions of Netscaler Gateway are affected by CVE-2025-6543?

Citrix NetScaler ADC and Gateway deployments are subject to confirmed active exploitation of a critical memory overflow vulnerability (CVE-2025-6543, CVSS 9.8) affecting VPN and authentication…. A patch is available.

Is there a public PoC exploit available for CVE-2025-6543?

Yes, a public proof-of-concept exploit is available for CVE-2025-6543. Prioritise patching immediately. EPSS: 2.0%.

How to fix or mitigate CVE-2025-6543?

Within 24 hours: Identify all NetScaler ADC and Gateway instances in production, especially those configured as VPN or AAA virtual servers, and isolate from internet-facing exposure pending patching. Within 7 days: Apply vendor-released security patch to all affected NetScaler systems; consult Citrix advisory for exact remediated versions. Within 30 days: Conduct forensic review of NetScaler access logs and authentication records dating back 90 days to identify potential compromise; validate no unauthorized VPN or administrative access occurred.

Netscaler Gateway CVE-2025-6543

EUVD-2025-19085 CRITICAL

Buffer Overflow (CWE-119)

2025-06-25 secure@citrix.com

Citrix Denial Of Service Netscaler Gateway Netscaler Application Delivery Controller

9.8

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

9.8 CRITICAL

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

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Analysis Updated

Apr 16, 2026 - 05:53 EUVD-patch-fix

executive_summary

Re-analysis Queued

Apr 16, 2026 - 05:29 backfill_euvd_patch

patch_released

Patch available

Apr 16, 2026 - 05:29 EUVD

37.236,47.46,59.19

EUVD ID Assigned

Mar 15, 2026 - 23:19 euvd

EUVD-2025-19085

Analysis Generated

Mar 15, 2026 - 23:19 vuln.today

Added to CISA KEV

Oct 24, 2025 - 13:42 cisa

CISA KEV

EUVD Exploitation Confirmed

Oct 24, 2025 - 13:42 euvd

EUVD KEV

PoC Detected

Oct 24, 2025 - 13:42 vuln.today

Public exploit code

CVE Published

Jun 25, 2025 - 13:15 nvd

CRITICAL 9.8

DescriptionCVE.org

Memory overflow vulnerability leading to unintended control flow and Denial of Service in NetScaler ADC and NetScaler Gateway when configured as Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) OR AAA virtual server

AnalysisAI

Citrix NetScaler ADC and Gateway contain a memory overflow vulnerability (CVE-2025-6543, CVSS 9.8) leading to unintended control flow and denial of service when configured as VPN or AAA virtual server. KEV-listed with public PoC, this vulnerability paired with CVE-2025-5777 (memory overread) indicates a systemic weakness in NetScaler's VPN request processing that enables both data theft and remote code execution.

Technical ContextAI

Unlike the companion CVE-2025-5777 (memory overread for data theft), this vulnerability causes a memory overflow that corrupts control flow data. This can cause immediate denial of service (crashing the NetScaler) or, with careful exploitation, redirect execution to attacker-controlled code. The VPN/AAA functionality is the attack surface — the same components affected by the overread vulnerability, suggesting a shared root cause in request parsing.

RemediationAI

Apply Citrix security update for both CVE-2025-6543 and CVE-2025-5777. Prioritize if VPN/AAA is internet-facing. Consider taking VPN offline if patching is delayed. After patching: invalidate sessions, rotate TLS keys.