Application Delivery Controller FirmwareOperating system · Citrix

CVE-2021-22956

HIGH · 7.5 CVSS v3.1 Published 2021-12-07

Fix available

A fix is available. Upgrade to 10.2.9c / 11.1-65.23 or later.

See remediation →

84/100

Remediation priority · High

Remotely reachable No privileges Zero-click

Official description

NVD · unedited

An uncontrolled resource consumption vulnerability exists in Citrix ADC <13.0-83.27, <12.1-63.22 and 11.1-65.23 that could allow an attacker with access to NSIP or SNIP with management interface access to cause a temporary disruption of the Management GUI, Nitro API, and RPC communication.

Technical summary

dbcve analysis · high confidence

This is an uncontrolled resource consumption (DoS) vulnerability in Citrix ADC that allows an authenticated attacker with NSIP or SNIP management interface access to exhaust resources, causing temporary disruption to the Management GUI, Nitro API, and RPC communication.

MitigationUpgrade Citrix ADC to version 13.0-83.27, 12.1-63.22, or 11.1-65.23 or later to patch this vulnerability.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions

NVD · CPE data

Application Delivery Controller FirmwareOperating system

Affected:< 11.1-65.23>= 12.1, < 12.1-63.22>= 13.0, < 13.0-83.27

GatewayApplication

Affected:< 11.1-65.23>= 12.1, < 12.1-63.22>= 13.0, < 13.0-65.23

Sd WanApplication

Affected:< 10.2.9c>= 11.4.0, < 11.4.2

CVSS breakdown

From the vector

Attack vector: Network
Complexity: Low
Privileges: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

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

Am I affected?

dbcve checks

Work through these to decide whether this CVE applies to you.

Identify the Citrix product in use

Log into the management GUI or CLI and identify whether the device is Citrix ADC (Application Delivery Controller), Citrix Gateway, or Citrix SD-WAN. The product name appears on the login page or in the system information section.

Affected if The device runs any of these three products: Citrix ADC, Citrix Gateway, or Citrix SD-WAN.
Check the installed firmware version on Citrix ADC or Gateway

In the CLI, run 'show version' or access the GUI and navigate to System > Information to view the firmware build number (for example, 13.0 build 83.27).

Affected if The version is below 11.1-65.23, or between 12.1-0 and 12.1-63.21, or between 13.0-0 and 13.0-83.26 for Citrix ADC; or below 11.1-65.23, between 12.1-0 and 12.1-63.21, or between 13.0-0 and 13.0-65.22 for Citrix Gateway.
Check the installed software version on Citrix SD-WAN

Access the SD-WAN GUI or CLI and locate the software version under the System > Diagnostics or System > Information page.

Affected if The version is below 10.2.9c, or between 11.4.0 and 11.4.1.
Verify management interface accessibility

Confirm whether the NSIP (NetScaler IP) or SNIP (Subnet IP) management interface is accessible from untrusted networks. Check the ns.conf configuration or the GUI under Traffic Management > IP Routing > IP Addresses, and review any firewall rules allowing access to ports 443 or 80 on these IPs.

Affected if The NSIP or SNIP management interface is exposed to attackers without proper network segmentation or VPN requirements.

A user is affected if they run Citrix ADC, Gateway, or SD-WAN with a firmware version within the vulnerable ranges listed and the management interface is accessible to authenticated attackers.

Generated from the published advisory. Verify against your own configuration.

Remediation

dbcve · scoped

Upgrade available Upgrade to 10.2.9c / 11.1-65.23 / 11.4.2 or later

Fixed in 10.2.9c11.1-65.2311.4.2

Interim mitigation

Upgrade Citrix ADC to version 13.0-83.27, 12.1-63.22, or 11.1-65.23 or later to patch this vulnerability.

Recommended fix High confidence

Citrix ADC: upgrade to 13.0-83.27, 12.1-63.22, or 11.1-65.23; Gateway: upgrade to 13.0-65.23, 12.1-63.22, or 11.1-65.23; SD-WAN: upgrade to 10.2.9c or 11.4.2 or later

1. Identify the current Citrix ADC, Gateway, or SD-WAN version by checking the management GUI or running 'show version' via CLI
2. Confirm the current version is within the affected ranges: ADC < 11.1-65.23, < 12.1-63.22, or < 13.0-83.27; Gateway < 11.1-65.23, < 12.1-63.22, or < 13.0-65.23; SD-WAN < 10.2.9c or < 11.4.2
3. Schedule a maintenance window for the upgrade
4. Backup the current configuration using 'save ns config' and export via management GUI or 'create backup'
5. Download the appropriate fixed firmware from citrix.com/support (13.0-83.27 for 13.x, 12.1-63.22 for 12.x, 11.1-65.23 for 11.x, or 10.2.9c/11.4.2 for SD-WAN)
6. Upload the new firmware via the management GUI (System > Firmware) or Nitro API
7. Install the firmware and reboot the device
8. After reboot, verify the new version is installed using 'show version'

Caveat Review release notes for your specific version upgrade path for any configuration or feature changes

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Application Delivery Controller Firmware Scoped from the published advisory

Consultation2.0 h
Implementation4.0 h
Testing2.0 h
Review / QA1.0 h

9.0 hours of engineering $1,600

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Scan for this in your stack

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References

Primary sources

support.citrix.comVendor Advisory
nvd.nist.govNVD record

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-22956 in production — separate from our analysis above.

Notes0 Guidelines

Know something about CVE-2021-22956?

The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.

The version that genuinely resolved it — not the one the vendor claimed
A config change or rule that shut the vector down
A gotcha in the upgrade path that cost you an afternoon

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here

Verified mitigations, workarounds, and config changes
Version or environment caveats, and links to real fixes
No weaponised exploit code, or anything meant to cause harm
No spam, self-promotion, credentials, or personal data

At a glance

A fix existsUpgrade to 10.2.9c / 11.1-65.23 or later

Severity 7.5 High

Exploit likelihood EPSS, next 30 days 0.9%

Affects: Application Delivery Controller Firmware

Remediation

A high-priority fix

Fix this in Application Delivery Controller Firmware 9 hrs · Moderate

Typical engagement from $1,600

Get a fix See the full breakdown ↓

A high-priority vulnerability. Send your environment and a specialist will scope CVE-2021-22956 and return a fixed quote and timeline.

You’ll deal with our team directly and deploy the reviewed fix to staging first — never straight to production.

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

Check your environment

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

Scan for this in your stack

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Practitioner notes

No notes yet

Official description

Technical summary

Affected products & versions

CVSS breakdown

Am I affected?

Remediation

References