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CVE-2026-88773 – HTTP Request Smuggling – Citrix NetScaler ADC and NetScaler Gateway (before 14.1-73

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Summary

CVE-2026-88773 is a critical HTTP Request/Response Smuggling vulnerability (CWE-444: Inconsistent interpretation of HTTP requests) affecting Citrix NetScaler ADC and NetScaler Gateway. The flaw arises from inconsistent parsing of HTTP requests/responses across the appliance’s processing paths, which can let an attacker desynchronize how requests are interpreted by front-end and back-end components. It carries a CVSS v4.0 base score of 9.3 (Critical) and does not require authentication or user interaction to exploit over the network.

Technical details

  • Root cause: NetScaler ADC/Gateway inconsistently interprets the boundaries of HTTP requests and responses, a classic condition for HTTP request/response smuggling (CWE-444).
  • Trigger conditions: Applies to NetScaler appliances configured with load balancing, content switching, VPN, or authentication (AAA) virtual servers of type HTTP or SSL.
  • Attack vector: Network-based, no privileges or user interaction required (AV:N/AC:L/AT:N/PR:N/UI:N).
  • Impact: Successful exploitation can allow an attacker to smuggle requests/responses past the appliance, undermining the integrity of subsequent request handling (high integrity impact to the vulnerable system and downstream/subsequent systems); this can be leveraged to bypass security controls, poison caches, hijack sessions, or manipulate traffic routed through the device.

Affected software

  • Citrix NetScaler ADC: versions before 14.1-73.37
  • Citrix NetScaler ADC: versions before 13.1-64.23
  • Citrix NetScaler ADC (FIPS): versions before 14.1-73.37 FIPS
  • Citrix NetScaler ADC (FIPS/NDcPP): versions before 13.1-37.279 (FIPS and NDcPP)
  • Citrix NetScaler Gateway (FIPS): versions before 14.1-73.37 FIPS
  • Citrix NetScaler Gateway: versions before 13.1-64.23

Severity

  • CVSS v4.0 Base Score: 9.3 (Critical)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:H/SI:H/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade to the fixed builds identified by Citrix:
    • NetScaler ADC and NetScaler Gateway 14.1-73.37 or later
    • NetScaler ADC and NetScaler Gateway 13.1-64.23 or later
    • NetScaler ADC 14.1-FIPS 14.1-73.37 FIPS or later
    • NetScaler ADC 13.1-FIPS and 13.1-NDcPP 13.1-37.279 or later
  • If no patch can be applied immediately: Citrix has not published a workaround for this issue; restrict and monitor exposure of internet-facing NetScaler management and virtual server interfaces, and prioritize patching given the critical severity and the presence of other actively exploited flaws in the same security bulletin affecting the same product family.

References

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