CVE-2026-88778Network attack vector

TCP sequence prediction via weak ISN generation

Published Sep 27, 2026 · Updated Sep 27, 2026

TCP sequence prediction in Citrix ADC and Gateway before 13.1-64.23 and 14.1-73.37 allows remote attackers to predict TCP ISNs. The TCP stack generates initial sequence numbers predictably when Enhanced ISN Generation is disabled, exposing future values from prior connections. Exploitation requires a configured TCP-based virtual server and Enhanced ISN Generation disabled, enabling connection spoofing, session interference, and limited data exposure.

CVSS severity8.8
High
EPSS probability0.38%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

TCP sequence prediction in Citrix ADC and Gateway before 13.1-64.23 and 14.1-73.37 allows remote attackers to predict TCP ISNs. The TCP stack generates initial sequence numbers predictably when Enhanced ISN Generation is disabled, exposing future values from prior connections. Exploitation requires a configured TCP-based virtual server and Enhanced ISN Generation disabled, enabling connection spoofing, session interference, and limited data exposure.

The record

CVE
CVE-2026-88778
Published
Sep 27, 2026
Updated
Sep 27, 2026
Vendor
Citrix
Product
Citrix ADC
Classifications
CWE-342, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 27, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 27, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <13.1.37.279 FIPS and NDcPP
  2. Affected versionversion=0 <13.1-64.23
  3. Affected versionversion=0 <14.1-73.37
  4. Affected versionversion=0 <14.1-73.37 FIPS

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Citrix · Citrix ADCversion=0 <13.1.37.279 FIPS and NDcPP; version=0 <13.1-64.23; version=0 <14.1-73.37; version=0 <14.1-73.37 FIPS
Citrix · Citrix Gatewayversion=0 <13.1-64.23; version=0 <14.1-73.37

Published CVSS scores

8.8NetScaler CNACVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:H/SC:L/SI:L/SA:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-342Predictable Exact Value from Previous Values
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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