Citrix NetScaler Improper Input Validation
CVE-2026-88771 is a critical-severity improper input validation vulnerability in ADC from Citrix NetScaler, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 14.1-73.37, 13.1-64.23, 14.1-73.37 FIPS as the first without the flaw, so updating ADC to one of those releases or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on September 27, 2026, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update ADC to 14.1-73.37 or 13.1-64.23 or 14.1-73.37 FIPS or 13.1.37.279 FIPS and NDcPP, whichever matches your release line, or a later version.
- Update Gateway to 14.1-73.37 or 13.1-64.23, whichever matches your release line, or a later version.
- Update Netscaler Application Delivery Controller to 13.1-64.23 or 13.1.37.279 or 14.1-73.37, whichever matches your release line, or a later version.
- CISA's required action: 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.
- Read the advisory on support.citrix.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Citrix NetScaler | ADC | before 14.1-73.37; before 13.1-64.23; before 14.1-73.37 FIPS; before 13.1.37.279 FIPS and NDcPP | 14.1-73.37, 13.1-64.23, 14.1-73.37 FIPS, 13.1.37.279 FIPS and NDcPP |
| Citrix NetScaler | Gateway | before 14.1-73.37; before 13.1-64.23 | 14.1-73.37, 13.1-64.23 |
| Citrix | Netscaler Application Delivery Controller | 13.1 up to, but not including, 13.1-64.23; 13.1 up to, but not including, 13.1.37.279; 14.1 up to, but not including, 14.1-73.37; 14.1-66.68 through 14.1-73.37 | 13.1-64.23, 13.1.37.279, 14.1-73.37 |
| Citrix | Netscaler Gateway | 13.1 up to, but not including, 13.1-64.23; 14.1 up to, but not including, 14.1-73.37 | 13.1-64.23, 14.1-73.37 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 9.5 | Critical | CNA |
| CVSS 3.1 | 9.8 | Critical | NVD |
Official description
Improper input validation vulnerability in Citrix NetScaler ADC and Citrix NetScaler Gateway. This issue affects ADC: before 14.1-73.37, before 13.1-64.23, before 14.1-73.37 FIPS, and before 13.1.37.279 FIPS and NDcPP; Gateway: before 14.1-73.37 and before 13.1-64.23 leading to an unauthenticated attacker to execute arbitrary commands.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Input Validation
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
How developers prevent this class of flaw
- Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build recognizers for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses.
- Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
- Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Record last changed materially (score, affected products, status or references).
- Deadline for US federal agencies to remediate, set by CISA.
References
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-88771US Government Resource
Our coverage
Other vulnerabilities in ADC
- 7.5 High severity
- 9.8 Critical severity
- 9.8 Critical severity
- 9.8 Critical severity
- 7.2 High severity
- 10.0 Critical severity
Recent Improper Input Validation vulnerabilities
- 9.6 Critical severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 8.6 High severity
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