CVE-2025-6543: Citrix NetScaler ADC and Gateway Buffer Overflow Vulnerability

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Yes, if you run Citrix NetScaler ADC and Gateway. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2025-06-30, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2025-07-21; treat that as the outer limit, not the target.
• EPSS 10.6%, percentile 96: FIRST’s model estimates a 10.6% chance of exploitation activity in the next 30 days, higher than 96% of all scored CVEs (very high). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Editorial verdict: Check exposure. Citrix Bleed 2: NetScaler Gateway Memory Leak — A pre-auth memory leak on internet-facing VPN gateways that was exploited within weeks; patched since June 2025, so the job now is proving you patched, killed sessions and were not session-hijacked.

What it is

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

CISA’s summary

Citrix NetScaler ADC and Gateway contain a buffer overflow vulnerability leading to unintended control flow and Denial of Service. NetScaler must be configured as Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) OR AAA virtual server.

Weakness type: CWE-119.

Product: Citrix NetScaler ADC and Gateway · Assigned by: Citrix · Published: 2025-06-25

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: high (needs special conditions)
• Attack requirements: present (depends on deployment conditions)
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: added 2025-06-30; federal due date 2025-07-21. Known ransomware use: Unknown.
• CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
• CISA SSVC assessment: exploitation active, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 10.56% probability of exploitation activity in the next 30 days; percentile 96.

Timeline

• 2025-06-17 — erroneo.us brief: Citrix Bleed 2: NetScaler Gateway Memory Leak
• 2025-06-25 — CVE record published by Citrix
• 2025-06-30 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2025-07-21 — CISA remediation deadline for US federal agencies
• 2026-02-26 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. Listed in CISA KEV notes (support.citrix.com) support.citrix.com
2. Listed in CISA KEV notes (netscaler.com) netscaler.com

Vulnerability records

1. CVE.org record CVE-2025-6543 cve.org
2. NVD entry CVE-2025-6543 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov

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