CriticalCVE-2025-5777

    NetScaler ADC and NetScaler Gateway - Insufficient input validation leading to memory overread (CVE-2025-5777)

    Published Last modified In CISA KEV since Sources: CVE.org, NCSC NZ, pwn.watch, CERT-EU

    What is affected, what to do

    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

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update NetScaler ADC to version 43.56, NetScaler ADC to version 58.32, NetScaler Gateway to version 43.56. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • NetScaler ADC lt 14.1..43.56
    • NetScaler ADC lt 13.1..58.32
    • NetScaler Gateway lt 14.1..43.56
    • NetScaler Gateway lt 13.1..58.32
    Fixed in
    • NetScaler ADC 43.56
    • NetScaler ADC 58.32
    • NetScaler Gateway 43.56
    • NetScaler Gateway 58.32

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.3

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v4

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: CVE.org, NCSC NZ, pwn.watch, CERT-EU

    99.97 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.98

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    261.01 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: VulnCheck KEV (opens in a new tab), ANSSI / CERT-FR, NCSC NZ How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.3 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.5
    CVSS v4

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.3
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    99.97 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.98
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-125

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is network-reachable without authentication and sits in exactly the component exposed at the perimeter as your VPN and Citrix ICA entry point. Leaked memory includes session tokens that let attackers bypass MFA and take over fully authenticated remote sessions, mirroring the original "CitrixBleed" pattern. Exploitation likelihood is among the highest of any CVE, and CISA flags known use in ransomware campaigns, so this initial access is actively monetised in extortion chains. Treat any internet-facing NetScaler with a Gateway or AAA vServer as a critical emergency: patching plus session termination overrides normal change windows, and any unpatched exposure since July 2025 should be investigated as a potential compromise.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Scope your exposure (first hour): Enumerate every NetScaler ADC/Gateway appliance acting as a Gateway (VPN vServer, ICA Proxy, CVPN, RDP Proxy) or AAA vServer. Check the build with show ns version. Pure load-balancing instances without Gateway or AAA vServers are not affected per the description.

      • Patch now: Upgrade to the fixed builds:

        • 14.1 → 14.1-43.56 or later
        • 13.1 → 13.1-58.32 or later
        • 13.1-FIPS/NDcPP → 13.1-37.235
        • 12.1-FIPS → 12.1-55.328

        Non-FIPS 12.1 and 13.0 are end-of-life and will not receive a fix. Migrate them to a supported branch or pull them off the internet until you can.

      • Kill all sessions after patching: The memory overread can leak session tokens, and existing sessions survive the upgrade. Run the following on every node, including HA pairs and clusters: kill icaconnection -all, kill pcoipConnection -all, kill aaa session -all, kill rdp connection -all, clear lb persistentSessions.

      • Preserve evidence first: Collect /var/log/ns.log*, /var/nslog/ and ns.conf before any reboot or upgrade overwrites artefacts. Then hunt for:

        • unknown admin accounts
        • new responder or rewrite policies
        • webshells under /var/netscaler/logon/ and /var/vpn/

      • Rotate credentials on suspicion: If you find suspicious sessions, rotate:

        • nsroot and other NetScaler admin passwords
        • LDAP bind accounts and RADIUS shared secrets
        • passwords of privileged users who authenticated through the gateway

      • Check reporting obligations: On confirmed exploitation, observe the NIS2 deadlines towards your national CSIRT/authority: early warning within 24 h, notification within 72 h.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation and exposure: Where business allows, restrict Gateway and AAA vServers to known source ranges (partner IPs, geo-IP filtering on the upstream firewall). The management interface (NSIP, SSH/HTTPS) must never be internet-reachable.
      • Upstream IPS/WAF: Enable current Suricata/ET signatures for CVE-2025-5777. Block anomalous POSTs to /p/u/doAuthentication.do, especially bodies with a login parameter that lacks an = value assignment. The same logic can be built as a NetScaler responder policy (DROP/RESET); test it in log-only mode first.
      • Rate limiting: Throttle repeated requests to the authentication endpoints per source, using a NetScaler rate-limit identifier or the edge firewall. Exploitation typically involves high-frequency requests to harvest memory fragments.
      • Session hardening: Shorten session and forced timeouts. MFA alone does not help, because stolen tokens represent already-authenticated sessions. Bind sessions to client IP where feasible.
      • IAM and least privilege: Limit internal resources reachable through the gateway to what is needed. Route admin access to AD and hypervisors exclusively via dedicated PAWs or jump hosts, never directly from VPN address pools.

    3. Runbook step 3

      Detection rules

      • NetScaler ns.log: Authentication is rejected for entries containing garbled or binary characters in the username field indicate memory-leak probing. Hunt with: grep -a "Authentication is rejected for" /var/log/ns.log | grep -aP "[^\x20-\x7E]".
      • Session hijacking: The same session ID or user appearing from multiple source IPs within a short window. Use SSLVPN LOGIN/TCPCONNSTAT events and the Client_ip and Nat_ip fields. Example (SPL): index=netscaler "SSLVPN" | stats dc(client_ip) as ips by session_id user | where ips>1.
      • Web and proxy logs: Bursts of POSTs to /p/u/doAuthentication.do from a single source, unusual response sizes, or <InitialValue> content in responses. NetScaler does not log HTTP by default, so source this from AppFlow/web logging or an upstream reverse proxy or WAF.
      • Network telemetry (Zeek/Suricata): Signature hits for CVE-2025-5777. Also watch for lateral movement from the VPN pool: RDP, SMB and LDAP to domain controllers, or admin tooling shortly after VPN logons from new devices.
      • Windows follow-on activity: Event ID 4624 (logon type 10/3) from VPN-pool IPs at unusual hours, and 4720/4728 (account and group changes). Sysmon EID 1 on servers showing remote-admin tools or ransomware precursors such as network scanners and vssadmin delete shadows.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    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

    Source: NVD (NIST), CISA KEV Catalog, CVE.org (MITRE), NCSC NZ (CC BY 4.0), pwn.watch, cvelistv5, certeu_advisory

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    NetScalerADC
    • 13.1 – < 58.32
    • 14.1 – < 43.56
    • 58.32
    • 43.56
    NetScalerGateway
    • 14.1 – < 43.56
    • 13.1 – < 58.32
    • 43.56
    • 58.32
    citrixnetscaler_application_delivery_controller
    • 13.1 – < 13.1-37.235
    • 13.1 – < 13.1-58.32
    • 12.1 – < 12.1-55.328
    • 14.1 – < 14.1-43.56
    • 13.1-37.235
    • 13.1-58.32
    • 12.1-55.328
    • 14.1-43.56
    citrixnetscaler_gateway
    • 14.1 – < 14.1-43.56
    • 13.1 – < 13.1-58.32
    • 14.1-43.56
    • 13.1-58.32

    Vendors and products

    Weakness classes (CWE)

    • CWE-125Out-of-bounds Read

      Base

      The product reads data past the end, or before the beginning, of the intended buffer.

      Entry at MITRE CWE-125

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    NCSC NZCVE-2025-6543 affecting Citrix Netscaler products (opens in a new tab)NCSC NZactively exploited
    ANSSI / CERT-FRLicence Ouverte 2.0, as of CERTFR-2025-ALE-009 – Multiples vulnérabilités dans Citrix NetScaler ADC et NetScaler Gateway (clôturée 2025-08-18) (opens in a new tab)cert.cyber.gouv.fractively exploited
    PoC-in-GitHub (nomi-sec)cve-2025-5777-citrixbleed2_reproduction (opens in a new tab)github.comPoC (publicly reported)reported, not verified
    PoC-in-GitHub (nomi-sec)CVE-2025-5777 (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    References & sources

    • support.citrix.comsupport-home/kbsearch/article?articleNumber=CTX693420
    • doublepulsar.comcitrixbleed-2-exploitation-started-mid-june-how-to-spot-it-f310…Third-party advisory, Technical description, signature
    • reliaquest.comCVE-2025-5777: Citrix Bleed 2 Opens Old Woundsmedia-coverage, pwn-watch
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2025-5777government-resource
    • bleepingcomputer.comnews/security/cisa-tags-citrix-bleed-2-as-exploited-gives-agenc…
    • labs.watchtowr.comHow Much More Must We Bleed? (CitrixBleed 2)pwn-watch
    • theregister.com2025/07/10/cisa_citrixbleed_kev
    • horizon3.aiattack-research/attack-blogs/cve-2025-5777-citrixbleed-2-write-…
    • netscaler.comblog/news/netscaler-critical-security-updates-for-cve-2025-6543…
    • citrixbleed.com
    • cert.cyber.gouv.frANSSI / CERT-FR: CERTFR-2025-ALE-009 – Multiples vulnérabilités dans Citrix NetScaler ADC et NetScaler Gateway (clôturée 2025-08-18)cert-fr
    • pwn.watchpwn.watch: CitrixBleed 2: NetScaler memory leak exploited to hijack sessionspwn-watch
    • greynoise.ioExploitation of CitrixBleed 2 Began Before PoC Was Publicpwn-watch
    • NVD (NIST)NVD: CVE-2025-5777pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch

    Reanalysis & status changes

    Chronological NVD audit events for this CVE — reanalyses, CVSS updates, CPE diffs.

    1. Modified Analysisnvd@nist.gov

    2. CVE Modifiedsecure@citrix.com

      • Reference: after https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX693420
      • Reference: before https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX693420
      • Reference Type: before https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX693420 Types: Vendor Advisory

    3. CVE Modified134c704f-9b21-4f2e-91b3-4a467353bcc0

      • CWE: before CWE-457
      • Reference: after https://doublepulsar.com/citrixbleed-2-exploitation-started-mid-june-how-to-spot-it-f3106392aa71
      • Reference: after https://reliaquest.com/blog/threat-spotlight-citrix-bleed-2-vulnerability-in-netscaler-adc-gateway-devices/
      • Reference: after https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-5777

    4. CVE Modifiedaf854a3a-2127-422b-91ae-364da2661108

      • Reference: after https://citrixbleed.com
      • Reference: after https://horizon3.ai/attack-research/attack-blogs/cve-2025-5777-citrixbleed-2-write-up-maybe/
      • Reference: after https://labs.watchtowr.com/how-much-more-must-we-bleed-citrix-netscaler-memory-disclosure-citrixbleed-2-cve-2025-5777/
      • Reference: after https://www.bleepingcomputer.com/news/security/cisa-tags-citrix-bleed-2-as-exploited-gives-agencies-a-day-to-patch/
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