CriticalCVE-2019-11634

    Citrix Workspace Application and Receiver for Windows Remote Code Execution Vulnerability (CVE-2019-11634)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    Citrix Workspace App before 1904 for Windows has Incorrect Access Control.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Citrix Workspace to version 1904. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Citrix Receiver eq 4.9..4.9
    • Citrix Workspace lt *..1904
    Fixed in
    • Citrix Workspace 1904

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

    Metrics

    9.8

    Priority

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

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: CVE.org

    8.1 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 94.8

    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
    245.90 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 exploited
    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
    9.8 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
    9.8
    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“.

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    8.1 %
    Moderate — model estimates 1-10% exploitation likelihood.
    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
    94.8
    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
    CISA assessment (SSVC)
    Exploitation: active · automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 26 October 2021
    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-284

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is network-reachable without authentication and inverts the usual trust model: the attacker controls the server side and compromises the client as soon as a user connects to a malicious or hijacked Citrix host. CISA flags it as used in ransomware campaigns. Typical entry vectors are weaponised .ica files delivered by phishing or compromised supplier environments that lead into the corporate network. Exploitation likelihood is high, though not in the very top tier. Organisations with many external Citrix touchpoints (suppliers, hospitals, public-sector portals) or lingering Receiver installs should treat it as urgent. Where clients connect only to your own hardened infrastructure, it remains high priority but can follow the regular patch cycle.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory every client: Find all Windows endpoints running Citrix Workspace App or Citrix Receiver via software inventory, Intune or SCCM. Check the DisplayVersion value under HKLM\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall\CitrixOnlinePluginPackWeb. All Workspace App builds before 1904 and Receiver for Windows are affected.
      • Patch: Upgrade Citrix Workspace App for Windows to 1904 or later, ideally the current LTSR or CR build. For Receiver for Windows, a patch is available from the vendor — look up the fixed version in the vendor advisory. Receiver is end-of-life, so plan the migration to Workspace App now.
      • Disable Client Drive Mapping (CDM) on unpatched clients: Use GPO with the Citrix Workspace ADMX template (Remoting client devices → Client drive mapping) and disable all drives. The flaw is that user-defined local drive access preferences are not enforced. A malicious or compromised server can therefore read and write the client file system.
      • Restrict sessions to trusted endpoints: Allow ICA/HDX sessions only to your own StoreFront, Gateway or Citrix Cloud endpoints. Third-party portals, supplier environments and user-opened .ica files from the internet are the main risk.
      • Triage likely exposure first: Immediately hunt for persistence on endpoints whose users recently connected to non-corporate Citrix environments. Check Startup folders, Run keys and scheduled tasks (see Detection).

    2. Runbook step 2

      Mitigation layers

      • Network segmentation and egress control: Permit outbound TCP/UDP 1494 (ICA) and 2598 (Session Reliability) only to approved Citrix infrastructure IPs. Restrict HDX-over-TLS on 443 to known Gateway FQDNs via proxy allowlist.
      • Web proxy and content filtering: Block downloads of .ica files (MIME application/x-ica) from unapproved domains. These files auto-launch wfica32.exe and connect the client to the attacker's server.
      • Endpoint hardening with application control: Use AppLocker or WDAC to prevent execution from user-writable paths (%APPDATA%, %TEMP%, Startup folders). A payload dropped via CDM then cannot run.
      • Configuration hardening: Beyond CDM, tighten clipboard and device redirection for external stores. Pin allowed store URLs to your own StoreFront via GPO.
      • IAM and least privilege: Remove local admin rights from users. This limits what the Citrix client process can write and caps the blast radius of rogue file-system access.

    3. Runbook step 3

      Detection rules

      • Sysmon EID 11 (FileCreate): Flag events where Image ends with \wfica32.exe and TargetFilename contains \Start Menu\Programs\Startup\ or ends with .exe, .dll, .lnk, .bat, .ps1 or .hta. KQL: DeviceFileEvents | where InitiatingProcessFileName =~ "wfica32.exe" and FileName endswith_cs ".exe"
      • Sysmon EID 1 / EDR process ancestry: Look for unusual children of wfica32.exe, CDViewer.exe or SelfService.exe, such as cmd.exe, powershell.exe, rundll32.exe or mshta.exe. Also flag execution of any file previously written by wfica32.exe.
      • Sysmon EID 13 / Windows Security EID 4657: Watch for modifications to HKCU\...\CurrentVersion\Run that coincide with an active ICA session.
      • Network telemetry (Zeek/Suricata, firewall): Alert on 1494/2598 sessions to destinations outside approved Citrix infrastructure. Suricata idea: alert tcp $HOME_NET any -> !$CITRIX_SERVERS [1494,2598] (msg:"ICA to untrusted host"; flow:to_server,established; sid:...;)
      • Proxy logs: Flag responses with Content-Type: application/x-ica or URLs ending in .ica from unapproved domains.

    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

    Citrix Workspace App before 1904 for Windows has Incorrect Access Control.

    Source: CISA KEV Catalog, cvelistv5, NVD (NIST)

    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
    citrixreceiver
    • 4.9
    • —
    citrixworkspace
    • < 1904
    • 1904

    Vendors and products

    Weakness classes (CWE)

    • CWE-284Improper Access Control

      Pillar

      The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.

      Entry at MITRE CWE-284

    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

    References & sources

    • support.citrix.comv1/search?searchQuery=""&lang=en&sort=cr_date_desc&prod=&pver=&…x_refsource_MISC
    • support.citrix.comarticle/CTX251986x_refsource_CONFIRM
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2019-11634government-resource
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