CriticalCVE-2019-1253

    Microsoft Windows AppX Deployment Server Privilege Escalation Vulnerability (CVE-2019-1253)

    Published In CISA KEV since Sources: CVE.org

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    What is affected, what to do

    An elevation of privilege vulnerability exists when the Windows AppX Deployment Server improperly handles junctions.To exploit this vulnerability, an attacker would first have to gain execution on the victim system, aka 'Windows Elevation of Privilege Vulnerability'. This CVE ID is unique from CVE-2019-1215, CVE-2019-1278, CVE-2019-1303.

    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 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

    11.6 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 96.1

    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
    237.80 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
    11.6 %
    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
    96.1
    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

    This is a local privilege escalation that, once an attacker has a foothold, lifts a standard account to SYSTEM with low complexity and no user interaction — public exploit code has made it a reliable post-phishing or post-loader step in intrusion chains. CISA flags known ransomware use, and exploitation likelihood is rated high. Organisations with no Windows 10 1703/1709/1803 estate and full patch compliance carry little residual risk; where unpatched or unsupported clients remain — common in OT-adjacent, lab or manufacturing segments of critical-infrastructure operators — treat remediation as high priority and tie it to an upgrade programme.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Identify every endpoint running Windows 10 1703, 1709 or 1803 (affected per context) via Intune/SCCM queries on OS version or build number. These releases are out of mainstream servicing and remain vulnerable until upgraded.
      • Patch: Install the Microsoft security fix for CVE-2019-1253 or the latest cumulative update for the respective build. A patch is available from the vendor — look up the KB number in the MSRC advisory for CVE-2019-1253. Where hosts still run 1703/1709/1803, schedule an immediate feature upgrade to a supported Windows release.
      • Triage exposure: Prioritise unpatched legacy hosts with internet browsing or email clients (the usual initial-access vectors). Hosts that cannot be updated quickly should move to a quarantine VLAN or be placed under EDR network containment.
      • Compromise assessment: On hosts with malware or phishing incidents in recent months, hunt specifically for junction abuse under %LOCALAPPDATA%\Packages\ and permission changes on system files (see Detection rules).
      • Rotate credentials: If successful escalation is suspected, reset local admin passwords (LAPS) and any cached domain credentials on affected hosts — SYSTEM access enables LSASS dumping.

    2. Runbook step 2

      Mitigation layers

      • Application control: Configure WDAC or AppLocker to block binaries and scripts executing from user-writable paths (%TEMP%, %APPDATA%, %LOCALAPPDATA%, Downloads). Exploitation requires prior local code execution — denying that foothold is the most effective compensating control.
      • ASR rules (Defender for Endpoint): Enable "Block executable files from running unless they meet a prevalence, age, or trusted list criterion" and "Block Office applications from creating child processes" to break the typical macro → loader → LPE chain.
      • Least privilege: Restrict interactive logons on servers and admin workstations, enforce a tiering model, keep domain admins off clients. SYSTEM on a host matters far less when no high-privilege credentials are cached there.
      • Credential protection: Enable Credential Guard and LSA protection (RunAsPPL) so an escalation does not translate directly into domain compromise.
      • AppXSvc service: Disabling the AppX Deployment Service on Windows 10 clients is not recommended (breaks Start menu, Store apps and update flows). Consider it only for tightly scoped kiosk or special-purpose systems after testing.
      • Segmentation: Limit post-escalation lateral movement by blocking client-to-client SMB (TCP 445), RDP (TCP 3389) and WinRM (TCP 5985/5986) via host firewall.

    3. Runbook step 3

      Detection rules

      • Junction creation by standard users (Sysmon EID 1 / EDR): Process launches with cmd.exe /c mklink /J, PowerShell New-Item -ItemType Junction, or tools such as CreateMountPoint.exe targeting paths under \AppData\Local\Packages\. Sigma shape: CommandLine|contains|all: ['mklink', '/J'] AND CommandLine|contains: '\Packages\'.
      • Permission changes on system files (Windows Security EID 4670, requires SACL): SubjectUserSid = S-1-5-18 with ObjectName under C:\Windows\System32\ or C:\Program Files\, initiated by the wsappx svchost instance. KQL: SecurityEvent | where EventID == 4670 and ObjectName startswith "C:\\Windows\\System32" and ProcessName endswith "svchost.exe".
      • AppXSvc writing outside package paths (Sysmon EID 11 / EDR file events): svchost.exe -k wsappx creating or modifying files outside \AppData\Local\Packages\ or C:\Program Files\WindowsApps\ strongly indicates a redirected write.
      • Anomalous SYSTEM process chains (Sysmon EID 1): Following junction activity, look for processes at IntegrityLevel = System launched from a replaced system binary or DLL path. EDR correlation: user process → junction creation → SYSTEM process from tampered path shortly after.
      • Follow-on activity: LSASS access (Sysmon EID 10, GrantedAccess 0x1010/0x1FFFFF) or new service installation (System EID 7045) on the same host shortly after the above events.

    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 the Windows AppX Deployment Server improperly handles junctions.To exploit this vulnerability, an attacker would first have to gain execution on the victim system, aka 'Windows Elevation of Privilege Vulnerability'. This CVE ID is unique from CVE-2019-1215, CVE-2019-1278, CVE-2019-1303.

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

    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
    • 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_10_1903—
    Windowsmicrosoftwindows_server_1803—
    Windowsmicrosoftwindows_server_1903—
    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 StormAppXSvc 17763.1.amd64fre.rs5_release.180914 1434 Privilege Escalation (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—

    References & sources

    • portal.msrc.microsoft.comen-US/security-guidance/advisory/CVE-2019-1253x_refsource_MISC, Patch, Vendor advisory
    • packetstormsecurity.comfiles/154488/AppXSvc-17763.1.amd64fre.rs5_release.180914-1434-P…x_refsource_MISC, Third-party advisory, Vulnerability database
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2019-1253government-resource, US government resource
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