Vulnerability report

Active exploitation observed Confirmed confidence In CISA KEV

CVE-2025-5777

ADC

NetScaler / ADC · affected before 43.56

Watch CVE-2025-5777 Browse KEV feed
Severity
CVSS 9.3 · Critical
Confidence
Confirmed
Exploit status
Observed in sensors
EPSS
100.0%
First observed
12 Jun 2026
Last observed
08 Oct 2026

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2025-5777 is an unauthenticated vulnerability affecting NetScaler ADC, Gateway. Insufficient input validation leading to memory overread when the NetScaler is configured as a Gateway (VPN virtual server, ICA...

Is it exploited?

Yes. Previdian sensors observed exploitation attempts with confirmed confidence. Listed in CISA KEV. Also confirmed by third-party sources.

Who is affected?

NetScaler / ADC affected before 43.56.

What should we do?

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

Overview

ADC

Insufficient input validation leading to memory overread when the NetScaler is configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) OR AAA virtual server

NetScaler Affected
ADC
Before 43.56 Before 58.32
NetScaler Affected
Gateway
Before 43.56 Before 58.32
Published
17 Jun 2025
Exploitation Reported
01 Jun 2026
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

nuclei_scanner cisa malware

CVE References

Exploitation evidence

Why Previdian marks this CVE as exploited

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

Exploited in the wild

CVE

Recorded 01 Jun 2026

A trusted third party reported exploitation.

Active exploitation observed

Previdian sensor

First observed 27 Jun 2026

Previdian first observed exploitation attempts targeting this vulnerability in our honeypot sensors.

Used in malware

CVE

Recorded 02 Jun 2026

Malware families have been linked to exploitation of this CVE.

Proof of concept available

Nuclei Templates

Recorded 12 Jun 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 10:36 UTC
CISA 2026-06-02 14:07 UTC
Previdian Sensors 2026-07-01 08:30 UTC
The Hacker News 2026-07-02 20:20 UTC
Tenable Blog 2026-09-27 10:21 UTC
GreyNoise 2026-09-28 17:21 UTC

Operational indicators for this CVE are listed under Detection.

Sensor telemetry

First-party evidence of exploitation activity

Previdian sensors recorded exploitation attempts targeting this vulnerability. The cards and chart show volume, unique attackers, and daily activity.

97

Attempts observed

64

Unique attacker IPs

22

Attacker countries

AE · AU · CA · CH · DE · FI · GB · HK · IN · JP · LK · NL · PE · PL · PT · RO · SC · SE · TT · TW · US · YE

13

Sensors observed

CVE-2025-5777 exploitation attempts over the last 84 days

Daily events observed by Previdian sensors

Updated 09 Oct 2026

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18 Jul 4 Aug 21 Aug 7 Sep 9 Oct

First observed 12 Jun 2026 · Last observed 08 Oct 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
2
9
2

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/2025/CVE-2025-5777.yaml 01 Jun 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

100.0%

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 · GreyNoise

Swarming Against Citrix 0-Day Exploitation

On 24 September 2026, a malicious cyber actor (MCA) used 149.104.78.141 to attempt zero-day exploitation against a Citrix NetScaler Gateway. At the time, there were no CVE-specific detections for the attack due to it occurring pre-disclosure. However, GreyNoise still detected...

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 7.5 High

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

All Mentions

Recent mention · GreyNoise

Swarming Against Citrix 0-Day Exploitation

GreyNoise · 28 Sep 2026

On 24 September 2026, a malicious cyber actor (MCA) used 149.104.78.141 to attempt zero-day exploitation against a Citrix NetScaler Gateway. At the time, there were no CVE-specific detections for the attack due to it occurring pre-disclosure. However, GreyNoise still detected and labeled the activity as fundamentally malicious within seconds due to behavioral detections.

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 · Huntress Blog

CitrixBleed 2 (CVE-2025-5777) 7Steps to Dragonforce Ransomware | Huntress

Huntress Blog · 09 Jul 2026

Huntress has observed a series of strikingly similar intrusions beginning with CitrixBleed 2 exploitation, employing novel local privilege escalation techniques, and ending in Dragonforce ransomware.

Recent mention · The Hacker News

Ransomware Groups Turn to Citrix Bleed 2, BYOVD, and Supply Chain Credentials

The Hacker News · 02 Jul 2026

Threat actors associated with the Anubis ransomware operation have been observed exploiting the Citrix Bleed 2 (CVE-2025-5777) vulnerability to obtain initial access. "Although tactics differ between affiliates, common patterns emerged in tradecraft through use of legitimate Remote Management and Monitoring (RMM) tooling, credential access, and hands-on-keyboard procedures used for lateral

Potential Proof of Concepts

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

Citrix NetScaler Memory Disclosure - CitrixBleed 2

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation

  1. 17:21 UTC

    KEV confirmed by GreyNoise

    Exploitation attested by an external source

  2. 10:21 UTC

    KEV confirmed by Tenable Blog

    Exploitation attested by an external source

  3. 20:20 UTC

    KEV confirmed by The Hacker News

    Exploitation attested by an external source

  4. 10:21 UTC

    Observed by Previdian sensors

    Evidence-backed exploitation signal

  5. 14:21 UTC

    Public PoC available

    Public proof-of-concept code published

  6. 00:34 UTC

    Indicators of compromise added (84)

    Indicators of compromise recorded

  7. 14:07 UTC

    First public exploitation report

    Exploit observed in malware

  8. 14:07 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  9. 15:34 UTC

    Nuclei template available

    Scanner coverage available

  10. 10:36 UTC

    KEV confirmed by CVE

    Exploitation attested by an external source

  11. 00:00 UTC

    Added to Previdian KEV Feed

    High-confidence, third-party attested exploitation

  12. 12:29 UTC

    CVE published

    Vulnerability disclosed publicly

  13. 06:14 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

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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
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  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2025-5777

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2025-5777",
  "confidence": "Confirmed",
  "cvss_score": 9.3,
  "cvss_estimated": false,
  "epss_score": 0.99972,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": true
  },
  "sensor_telemetry": { "attempts": 97, "sensors": 13 }
}