CVE-2021-22955

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.

Published: 2021-12-07 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-22955 is rated Moderate Risk (49.5/100): CVSS High severity, with medium exploitation likelihood (EPSS 0.89%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-22955

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.51% 0.89% +0.38%
2 2025-10-09 0.67% 0.51% -0.16%
3 2025-03-30 — 0.67% —

Full EPSS history (10 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-22955

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-22955

Affected software / configurations for CVE-2021-22955

Vendor Product Version Raw CPE
citrix application_delivery_controller_firmware <= 11.1-65.23 cpe:2.3:o:citrix:application_delivery_controller_firmware:*:*:*:*:*:*:*:*
citrix application_delivery_controller_firmware >= 12.1, < 12.1-63.22 cpe:2.3:o:citrix:application_delivery_controller_firmware:*:*:*:*:*:*:*:*
citrix application_delivery_controller_firmware >= 13.0, < 13.0-83.27 cpe:2.3:o:citrix:application_delivery_controller_firmware:*:*:*:*:*:*:*:*
citrix gateway < 11.1-65.23 cpe:2.3:a:citrix:gateway:*:*:*:*:*:*:*:*
citrix gateway >= 12.1, < 12.1-63.22 cpe:2.3:a:citrix:gateway:*:*:*:*:*:*:*:*
citrix gateway >= 13.0, < 13.0-83.27 cpe:2.3:a:citrix:gateway:*:*:*:*:*:*:*:*

References for CVE-2021-22955

cvelogic Threat Intelligence