CriticalCVE-2019-0841

    Microsoft Windows AppX Deployment Service (AppXSVC) Privilege Escalation Vulnerability (CVE-2019-0841)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    An elevation of privilege vulnerability exists when Windows AppX Deployment Service (AppXSVC) improperly handles hard links, aka 'Windows Elevation of Privilege Vulnerability'. This CVE ID is unique from CVE-2019-0730, CVE-2019-0731, CVE-2019-0796, CVE-2019-0805, CVE-2019-0836.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft Windows eq 10 Version 1703 for 32-bit Systems..10 Version 1703 for 32-bit Systems
    • Microsoft Windows eq 10 Version 1703 for x64-based Systems..10 Version 1703 for x64-based Systems
    • Microsoft Windows eq 10 Version 1709 for 32-bit Systems..10 Version 1709 for 32-bit Systems
    • Microsoft Windows eq 10 Version 1709 for x64-based Systems..10 Version 1709 for x64-based Systems
    • Microsoft Windows eq 10 Version 1803 for 32-bit Systems..10 Version 1803 for 32-bit Systems
    • Microsoft Windows eq 10 Version 1803 for x64-based Systems..10 Version 1803 for x64-based Systems
    • Microsoft Windows eq 10 Version 1803 for ARM64-based Systems..10 Version 1803 for ARM64-based Systems
    • Microsoft Windows eq 10 Version 1809 for 32-bit Systems..10 Version 1809 for 32-bit Systems
    • Microsoft Windows eq 10 Version 1809 for x64-based Systems..10 Version 1809 for x64-based Systems
    • Microsoft Windows eq 10 Version 1809 for ARM64-based Systems..10 Version 1809 for ARM64-based Systems
    • Microsoft Windows eq 10 Version 1709 for ARM64-based Systems..10 Version 1709 for ARM64-based Systems
    • Microsoft Windows Server eq version 1709 (Core Installation)..version 1709 (Core Installation)
    • Microsoft Windows Server eq version 1803 (Core Installation)..version 1803 (Core Installation)
    • Microsoft Windows Server eq 2019..2019
    • Microsoft Windows Server eq 2019 (Core installation)..2019 (Core installation)

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

    Metrics

    7.8

    Priority

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

    Source: NVD, CVSS v3

    7.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: CVE.org

    41.4 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 98.7

    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
    241.89 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
    7.8 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
    7.8
    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“.

    Read in glossary
    41.4 %
    Elevated — model estimates 10-50% 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
    98.7
    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 · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 7 February 2025
    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-59

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The vulnerability is on the CISA KEV list and flagged for use in ransomware campaigns — typical usage is post-exploitation after initial user access (phishing, stolen RDP credentials) to pivot from standard user to SYSTEM, enabling lateral movement, credential dumping and encryption staging. The vector is local and needs only low privileges, but a reliable public exploit primitive exists and the exploitation likelihood ranks among the highest in the Microsoft portfolio per EPSS. Rate as HIGH priority for any estate with multi-user hosts, terminal servers or legacy Windows 10 builds; MEDIUM for single-user clients with strict application allowlisting. Hosts still on EOL builds (1703/1709/1803) should be classified "not patchable — accept risk formally or replace immediately".

    1. Runbook step 1

      Immediate response (0-24 h)

      • Deploy the Microsoft April 2019 security updates (Patch Tuesday, 2019-04-09) across all affected builds: Windows 10 1703/1709/1803/1809 and Windows Server 2016/2019. The MSRC advisory for CVE-2019-0841 lists the per-build KB IDs — validate the exact KB in the Update Catalog before rollout.
      • Identify end-of-life builds (Windows 10 1703, 1709, 1803) and either upgrade to a supported branch immediately or decommission them; those branches receive no patch and remain permanently vulnerable.
      • Prioritise multi-user systems: RDS/terminal servers, VDI pools, jump hosts and developer workstations first, because the flaw requires only an interactive logon of any user and the attack surface is maximal there.
      • Inventory local and service accounts with interactive logon rights; disable those without business justification, since the vulnerability escalates from standard user to SYSTEM without further prerequisites.
      • Until patch deployment completes: on servers that do not use UWP/Store apps, disable the AppX Deployment Service (sc config AppXSVC start= disabled) and roll via GPO. Validate impact on UWP apps and MDM-driven deployments first.
      • Keep an IR playbook ready for compromised hosts: EDR containment, credential rotation including KRBTGT where domain controllers are reachable, forensic image before reimage.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: isolate multi-user systems (RDS, Citrix, VDI) into dedicated enclaves with strict egress filtering to limit lateral movement after a successful local escalation.
      • IAM/least privilege: manage local admin passwords via LAPS, enforce a Tier-0/1 logon model on servers, apply AppLocker or WDAC policies against unsigned binaries in %LOCALAPPDATA%\Packages and %TEMP%.
      • Endpoint hardening: enable Microsoft Defender ASR rules, especially "Block abuse of exploited vulnerable signed drivers" and "Block credential stealing from LSASS"; run EDR with behavioural detection for token manipulation.
      • Filesystem monitoring: log hardlink creation by non-privileged users targeting sensitive paths (C:\Windows\System32, C:\ProgramData\Microsoft\Windows\AppRepository) via Sysmon FileCreate / FileCreateStreamHash (EID 11/15).
      • Configuration hardening: audit NTFS ACLs on AppX staging directories, set fsutil behavior set SymlinkEvaluation to the most restrictive policy (note: this covers symlinks only — hardlinks cannot be globally disabled, which is why the patch is non-negotiable).
      • Report patch compliance weekly via WSUS/SCCM/Intune; document exceptions (OT, medical devices) formally with compensating controls — a NIS2 Article 21 requirement.

    3. Runbook step 3

      Detection rules

      • Sysmon EID 1 (Process Create): svchost.exe -k wsappx -p -s AppXSVC as parent of unusual children (cmd.exe, powershell.exe, rundll32.exe) — Sigma shape: parent_image endswith svchost.exe AND parent_commandline contains AppXSVC AND image endswith (cmd.exe|powershell.exe).
      • Windows Security EID 4688 with TokenElevationType = TokenElevationTypeFull (1) for processes launched from user-writable paths (C:\Users\*, C:\ProgramData\*\Packages\*).
      • Sysmon EID 11 (FileCreate) for hardlink/junction activity under AppRepository, WindowsApps or Packages subfolders by non-SYSTEM accounts, correlated with a short-interval AppX install (EID 4697 Service Install).
      • EDR process ancestry: AppXSVC suddenly writing to protected system paths or modifying services — KQL shape in Defender XDR: DeviceFileEvents | where InitiatingProcessFileName == "svchost.exe" and InitiatingProcessCommandLine has "AppXSVC" and FolderPath startswith "C:\\Windows\\System32".
      • Inspect the Microsoft-Windows-AppXDeployment-Server/Operational log for failed or abnormal deployment transactions; repeated error events shortly before privilege-escalation indicators are a strong signal.

    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

    An elevation of privilege vulnerability exists when Windows AppX Deployment Service (AppXSVC) improperly handles hard links, aka 'Windows Elevation of Privilege Vulnerability'. This CVE ID is unique from CVE-2019-0730, CVE-2019-0731, CVE-2019-0796, CVE-2019-0805, CVE-2019-0836.

    Source: cvelistv5, CISA KEV Catalog, 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
    MicrosoftWindows
    • 10 Version 1803 for x64-based Systems
    • 10 Version 1709 for ARM64-based Systems
    • 10 Version 1809 for ARM64-based Systems
    • 10 Version 1709 for x64-based Systems
    • 10 Version 1703 for 32-bit Systems
    • 10 Version 1803 for 32-bit Systems
    • 10 Version 1703 for x64-based Systems
    • 10 Version 1809 for x64-based Systems
    • 10 Version 1809 for 32-bit Systems
    • 10 Version 1709 for 32-bit Systems
    • 10 Version 1803 for ARM64-based Systems
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    MicrosoftWindows Server
    • 2019
    • version 1709 (Core Installation)
    • 2019 (Core installation)
    • version 1803 (Core Installation)
    • —
    • —
    • —
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Windowsmicrosoftwindows_10_1703—
    Windowsmicrosoftwindows_10_1709—
    Windowsmicrosoftwindows_10_1803—
    Windowsmicrosoftwindows_10_1809—
    Windowsmicrosoftwindows_server_20161803
    Windowsmicrosoftwindows_server_2019—

    Weakness classes (CWE)

    • CWE-59Improper Link Resolution Before File Access ('Link Following')

      Base

      The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

      Entry at MITRE CWE-59

    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
    Packet StormMicrosoft Windows AppX Deployment Service Privilege Escalation (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—
    Packet StormInternet Explorer JavaScript Privilege Escalation (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—
    Packet StormMicrosoft Windows AppX Deployment Service Local Privilege Escalation (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—
    Packet StormMicrosoft Windows AppX Deployment Service Local Privilege Escalation (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—
    Packet StormAppXSvc Hard Link Privilege Escalation (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—
    Exploit-DBEDB-ID 46683 (opens in a new tab)exploit-db.comPoC (publicly reported)reported, not verified—

    References & sources

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