Microsoft Windows AppX Deployment Service (AppXSVC) Privilege Escalation
CVE-2019-1064 is a high-severity improper link resolution before file access vulnerability in Windows 10 Version 1703 from Microsoft, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists version publication as the first without the flaw, so updating Windows 10 Version 1703 to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on March 15, 2022, which means attacks have been observed in the wild, including in ransomware campaigns.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Windows 10 Version 1703 to publication or a later version.
- Update Windows 10 Version 1803 to publication or a later version.
- Update Windows Server, version 1803 (Server Core Installation) to publication or a later version.
- CISA's required action: Apply updates per vendor instructions.
- Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Windows 10 Version 1703 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1803 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server, version 1803 (Server Core Installation) | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1809 | 10.0.17763.0 up to, but not including, publication; 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server 2019 | 10.0.17763.0 up to, but not including, publication | publication |
| Microsoft | Windows Server 2019 (Server Core installation) | 10.0.17763.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1709 for 32-bit Systems | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1709 | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1903 for 32-bit Systems | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1903 for x64-based Systems | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1903 for ARM64-based Systems | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows Server, version 1903 (Server Core installation) | 10.0.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 Version 1607 | 10.0.14393.0 up to, but not including, publication | publication |
| Microsoft | Windows Server 2016 | 10.0.14393.0 up to, but not including, publication | publication |
| Microsoft | Windows Server 2016 (Server Core installation) | 10.0.14393.0 up to, but not including, publication | publication |
| Microsoft | Windows 10 1607 | Not specified in the record | Not stated |
| Microsoft | Windows 10 1703 | Not specified in the record | Not stated |
| Microsoft | Windows 10 1709 | Not specified in the record | Not stated |
| Microsoft | Windows 10 1803 | Not specified in the record | Not stated |
| Microsoft | Windows 10 1809 | Not specified in the record | Not stated |
| Microsoft | Windows 10 1903 | Not specified in the record | Not stated |
| Microsoft | Windows Server 1709 | Not specified in the record | Not stated |
| Microsoft | Windows Server 1803 | Not specified in the record | Not stated |
| Microsoft | Windows Server 1903 | Not specified in the record | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA (microsoft.com) |
| CVSS 3.1 | 7.8 | High | NVD |
| CVSS 2.0 | 7.2 | High | NVD |
Official description
An elevation of privilege vulnerability exists when Windows AppX Deployment Service (AppXSVC) improperly handles hard links. An attacker who successfully exploited this vulnerability could run processes in an elevated context. An attacker could then install programs; view, change or delete data. To exploit this vulnerability, an attacker would first have to log on to the system. An attacker could then run a specially crafted application that could exploit the vulnerability and take control of an affected system. The security update addresses the vulnerability by correcting how Windows AppX Deployment Service handles hard links.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Link Resolution Before File Access
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.
How developers prevent this class of flaw
- Follow the principle of least privilege when assigning access rights to entities in a software system. Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.
More Improper Link Resolution Before File Access vulnerabilities (CWE-59)
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-1064US Government Resource
Other vulnerabilities in Windows 10 Version 1703
- 7.8 High severity
Recent Improper Link Resolution Before File Access vulnerabilities
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
Apple OS X Authentication Bypass Exploited
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