CVE-2021-22955

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-12-07 · updated 2026-06-17
Weakness: CWE-400

Description

A unauthenticated denial of service vulnerability exists in Citrix ADC <13.0-83.27, <12.1-63.22 and 11.1-65.23 when configured as a VPN (Gateway) or AAA virtual server could allow an attacker to cause a temporary disruption of the Management GUI, Nitro API, and RPC communication.

Affected products

Citrix Application Delivery Controller Firmware: through 11.1-65.23; from 12.1 before 12.1-63.22; from 13.0 before 13.0-83.27 — fixed in 12.1-63.22, 13.0-83.27
NetScaler Gateway: before 11.1-65.23; from 12.1 before 12.1-63.22; from 13.0 before 13.0-83.27 — fixed in 11.1-65.23, 12.1-63.22, 13.0-83.27
Citrix ADC, Citrix Gateway: Citrix ADC 111.1, 2.1, 13.0,13.1

How to fix

Upgrade to a fixed version: Citrix Application Delivery Controller Firmware 12.1-63.22, 13.0-83.27; NetScaler Gateway 11.1-65.23, 12.1-63.22, 13.0-83.27. Check the vendor advisory for mitigations.

References

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