Citrix NetScaler ADC and NetScaler Gateway: denial of service flaw under attack

What is affected

Citrix NetScaler ADC and NetScaler Gateway is mostly run by companies, schools and public bodies, not on home computers. You are unlikely to have it yourself, but organisations that hold your data may. Breaches that start with flaws like this one are how personal data ends up leaked.

Citrix NetScaler ADC and NetScaler Gateway contain an improper restriction of operations within the bounds of a memory buffer vulnerability which could lead to denial of service.

What an attacker can do

This is a denial of service flaw. It lets an attacker crash the product or make it unavailable to the people who rely on it.

How it is reached

Over the internet or network

Access the attacker needs

No account needed

Does the victim have to do something?

No, works without the victim doing anything

What to do

1. At home: nothing to install. Keep your own devices updated and use a different password for every service, so that a breach at one organisation does not open your other accounts.
2. If you administer Citrix NetScaler ADC and NetScaler Gateway at work: apply the vendor's fix or mitigation now and review logs for signs of compromise, because the flaw was being exploited before it was listed.
3. If the product is past its support date and no fix exists, take it off the internet or retire it.

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Vendor advisories and fixes

• support.citrix.comsupport.citrix.com/support-home/kbsearch/article?articleNumber=CTX696604

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on August 26, 2026, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by August 29, 2026, a deadline that has already passed. That deadline does not bind anyone else, but it shows how seriously the agency rates it.

The EPSS model estimates a 1.0% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 62% of all scored vulnerabilities.

Its CVSS severity score is 8.8 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

Memory overflow vulnerability NetScaler ADC and NetScaler Gateway leading to unpredictable or erroneous behavior and Denial of Service if the appliance is configured as a Gateway (SSL VPN, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server