Microsoft Windows AppX Deployment Service (AppXSVC) Privilege Escalation
CVE-2019-0841 is a high-severity improper link resolution before file access vulnerability in Windows 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. Affected Windows versions: 10 Version 1703 for 32-bit Systems; 10 Version 1703 for x64-based Systems; 10 Version 1709 for 32-bit Systems, and others listed below. The record does not name a fixed version, so check the vendor advisory. 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
- Check which version of Windows you run against the affected versions below, and install the vendor's latest release.
- CISA's required action: Apply updates per vendor instructions.
- Read the advisory on portal.msrc.microsoft.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Windows | 10 Version 1703 for 32-bit Systems; 10 Version 1703 for x64-based Systems; 10 Version 1709 for 32-bit Systems; 10 Version 1709 for x64-based Systems; 10 Version 1803 for 32-bit Systems; 10 Version 1803 for x64-based Systems; 10 Version 1803 for ARM64-based Systems; 10 Version 1809 for 32-bit Systems; and 3 more ranges | Not stated |
| Microsoft | Windows Server | version 1709 (Core Installation); version 1803 (Core Installation); 2019; 2019 (Core installation) | 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 Server 2016 | 1803 | Not stated |
| Microsoft | Windows Server 2019 | 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 | NVD |
| CVSS 3.1 | 7.8 | High | CISA (ADP) |
| 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, 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: 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
Third-party and government advisories
- packetstormsecurity.com/files/152463/Microsoft-Windows-AppX-Deployment-Service-Privilege-Escalation.htmlThird Party Advisory, VDB Entry
- packetstormsecurity.com/files/153009/Internet-Explorer-JavaScript-Privilege-Escalation.htmlThird Party Advisory, VDB Entry
- packetstormsecurity.com/files/153114/Microsoft-Windows-AppX-Deployment-Service-Local-Privilege-Escalation.htmlThird Party Advisory, VDB Entry
- packetstormsecurity.com/files/153215/Microsoft-Windows-AppX-Deployment-Service-Local-Privilege-Escalation.htmlThird Party Advisory, VDB Entry
- zerodayinitiative.com/advisories/ZDI-19-360/Third Party Advisory, VDB Entry
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-0841US Government Resource
Technical write-ups (may include proof of concept)
- packetstormsecurity.com/files/153642/AppXSvc-Hard-Link-Privilege-Escalation.htmlExploit, Third Party Advisory, VDB Entry
- exploit-db.com/exploits/46683/Exploit, Third Party Advisory, VDB Entry
Other vulnerabilities in Windows
- 7.4 High severity
- 7.4 High severity
- 7.8 High severity
- 7.5 High severity
- 7.0 High severity
- 7.8 High severity
Recent Improper Link Resolution Before File Access vulnerabilities
- 7.8 High severity
- 7.8 High severity
Apple OS X Authentication Bypass Exploited
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