Vulnerability report

Exploitation Attempts Observed Confirmed Confidence In CISA KEV

CVE-2026-3055

Insufficient input validation leading to memory overread

NetScaler / ADC · affected before 66.59

Watch CVE-2026-3055 Browse KEV feed
Severity
CVSS 9.3 · Critical
Confidence
Confirmed
Exploit status
Exploitation Attempts Observed in the Wild
EPSS
91.5%
First observed
12 Jun 2026
Last observed
09 Nov 2026

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2026-3055 is an unauthenticated Insufficient input validation leading to memory overread affecting NetScaler ADC, Gateway.

Have exploitation attempts been observed?

Yes. Previdian sensors have observed 69 exploitation attempts, 32 unique attacker IPs, and 19 countries targeting CVE-2026-3055. First observed Jun 12, 2026; last observed Nov 09, 2026. Listed in CISA KEV. Also reported by third-party sources. Confidence is confirmed.

Who is affected?

NetScaler / ADC and Gateway, including affected before 66.59, affected before 62.23, and affected before 37.262.

What should we do?

Patch immediately, validate internet-facing exposure, and monitor for matching requests.

Overview

Insufficient input validation leading to memory overread

Insufficient input validation in NetScaler ADC and NetScaler Gateway when configured as a SAML IDP leading to memory overread

NetScaler Affected
ADC
Before 66.59 Before 62.23 Before 37.262
NetScaler Affected
Gateway
Before 66.59 Before 62.23
Published
23 Mar 2026
Exploitation Attempts Reported
01 Jun 2026
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

cisa nuclei_scanner metasploit_scanner

CVE References

Exploitation evidence

Evidence of exploitation attempts

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploitation Attempts Observed in the Wild

The Shadowserver

Recorded 01 Jun 2026

A trusted third party reported exploitation attempts.

Exploitation Attempts Observed

Previdian sensor

First observed 12 Jun 2026

Previdian sensors observed exploitation attempts targeting this vulnerability.

Proof of concept available

GitHub

Recorded 31 Mar 2026

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

Learn about Pro API access
Source Added
The Shadowserver First 2026-06-01 00:00 UTC
CVE 2026-06-01 12:26 UTC
CISA 2026-06-02 14:02 UTC
Previdian Sensors 2026-07-02 17:48 UTC
Tenable Blog 2026-09-27 10:21 UTC

Operational indicators for this CVE are listed under Detection.

Sensor telemetry

Previdian Sensor Observations

Previdian sensor observations are exploitation attempts targeting this vulnerability. They do not show that the target was vulnerable or that the attempt succeeded. The cards and chart show volume, unique attackers, and daily activity.

69

Attempts observed

32

Unique attacker IPs

19

Attacker countries

AE · BG · CH · CN · DE · FI · FR · GB · ID · JP · KZ · LU · NL · RO · SC · SG · UA · US · YE

29

Sensors observed

CVE-2026-3055 exploitation attempts over the last 86 days

Daily events observed by Previdian sensors

Updated 12 Nov 2026

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19 Aug 6 Sep 24 Sep 12 Oct 12 Nov

First observed 12 Jun 2026 · Last observed 09 Nov 2026

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Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
User-Agents
Callback hosts
1
14
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

Attacker IP Indicators

Attacker IP indicators observed · available in Pro and Enterprise.

Sensor-derived attacker IP indicators are available to Pro and Enterprise accounts under Detection and through the Pro API.

Learn about Pro API access

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Nuclei https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-3055.yaml 01 Jun 2026
Metasploit https://github.com/rapid7/metasploit-framework/blob/master/modules/auxiliary/scanner/http/citrix_netscaler_cve_2026_3055.rb 23 Mar 2026

Risk and context

Severity, weaknesses, and research context

CVSS v4.0

9.3 Critical

Potential damage if exploited. Separate from whether attackers are using it.

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

EPSS

91.5%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Out-of-bounds Read CWE-125

Recent mention · Tenable Blog

Frequently asked questions about reported Citrix NetScaler zero-day vulnerabilities

There are reportedly two unpatched zero-day Citrix NetScaler vulnerabilities capable of enabling remote code execution that have been actively exploited in the wild, with no patches available at this time.Key takeawaysReports indicate that there are two critical zero-day...

Read full advisory

All CVSS Scores

CVSS v4.0 9.3 Critical

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

CVSS v3.1 9.8 Critical

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

All Mentions

Recent mention · Tenable Blog

Frequently asked questions about reported Citrix NetScaler zero-day vulnerabilities

Tenable Blog · 27 Sep 2026

There are reportedly two unpatched zero-day Citrix NetScaler vulnerabilities capable of enabling remote code execution that have been actively exploited in the wild, with no patches available at this time.Key takeawaysReports indicate that there are two critical zero-day vulnerabilities in Citrix NetScaler.The reports originate from a pre-notification sent out ahead of public disclosure, so there are currently no specific details about these flaws and no patches available.This post will be updated as new information becomes available.BackgroundTenable's Research Special Operations (RSO)...

Recent mention · RecordedFuture

August 2026 CVE Landscape

RecordedFuture · 08 Sep 2026

In August 2026, Insikt Group® identified 73 high-impact vulnerabilities that should be prioritized for remediation, 43 of which had a Very Critical Recorded Future Risk Score. This represents a 14% decrease from last month.

Recent mention · Tenable Blog

The Agentic AI threat cluster: Seven incidents, three actors, and what they mean for your exposure

Tenable Blog · 15 Aug 2026

Tenable’s Research Special Operations (RSO) team has been tracking a cluster of agentic AI threat activity since late July 2026. The Taiwan autonomous AI cyber attack confirmed what the cluster data already showed: near-autonomous offensive AI has crossed from theoretical risk to operational reality.Key TakeawaysTaiwan's Ministry of Digital Affairs confirmed a near-autonomous AI cyber attack in July 2026 in which autonomous agents mapped 21 connected government systems, compromised 85 accounts, and exfiltrated more than 2,564 personnel records in approximately four days.The Taiwan campaign...

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

Citrix NetScaler SAML IDP - Memory Overread

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation attempts

  1. 10:21 UTC

    KEV confirmed by Tenable Blog

    Exploitation attempts reported by an external source

  2. 14:21 UTC

    Public PoC available

    Public proof-of-concept code published

  3. 00:34 UTC

    Indicators of compromise added (53)

    Indicators of compromise recorded

  4. 00:34 UTC

    Observed by Previdian sensors

    Previdian sensors observed exploitation attempts targeting this vulnerability.

  5. 14:02 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  6. 15:34 UTC

    Nuclei template available

    Scanner coverage available

  7. 12:26 UTC

    KEV confirmed by CVE

    Exploitation attempts reported by an external source

  8. 00:00 UTC

    Added to Previdian KEV Feed

    High-confidence, third-party report of exploitation attempts

  9. 20:21 UTC

    CVE published

    Vulnerability disclosed publicly

  10. 00:00 UTC

    Metasploit module available

    Exploit module available

  11. 18:00 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2026-3055

Sample API response 
{
  "cve_id": "CVE-2026-3055",
  "confidence": "Confirmed",
  "cvss_score": 9.3,
  "cvss_estimated": false,
  "epss_score": 0.91491,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": true
  },
  "sensor_telemetry": { "attempts": 69, "sensors": 29 }
}