AppXSvc 17763 – Arbitrary File Overwrite (DoS)

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• 作者： Gabor Seljan
  日期： 2019-12-11
• 类别：

  • dos
  平台：

  • windows
• 来源：https://www.exploit-db.com/exploits/47768/

• # Exploit Title: AppXSvc 17763 - Arbitrary File Overwrite (DoS)
  # Date: 2019-10-28
  # Exploit Author: Gabor Seljan
  # Vendor Homepage: https://www.microsoft.com/
  # Version: 17763.1.amd64fre.rs5_release.180914-1434
  # Tested on: Windows 10 Version 1809 for x64-based Systems
  # CVE: CVE-2019-1476
  
  # Summary:
  # AppXSvc improperly handles file hard links resulting in a low privileged user
  # being able to overwrite an arbitrary file leading to elevation of privilege.
  
  # Description:
  
  # An elevation of privilege vulnerability exists when the AppX Deployment Server
  # (AppXSvc) improperly handles file hard links. While researching CVE-2019-0841
  # originally reported by Nabeel Ahmed, I have found that AppXSvc can be forced
  # to overwrite an arbitrary file by deleting all registry data files before
  # creating the file hard link. As Nabeel Ahmed described in his write-up of
  # CVE-2019-0841, if the settings.dat file is corrupted it will be replaced with
  # the original settings.dat template. However, additional settings.dat.LOG1 and
  # settings.dat.LOG2 files are also created during the initialization process.
  # Substituting the settings.dat.LOG1 or the settings.dat.LOG2 file with a hard
  # link allows a low privileged user to overwrite an arbitrary file with registry
  # data or just simply empty it, respectively. A low privileged user could exploit
  # this vulnerability to cause denial of service by overwriting critical system
  # files.
  
  Steps to reproduce:
  1. Terminate Paint 3D processes.
  2. Delete settings.* files in Microsoft.MSPaint_8wekyb3d8bbwe\Settings folder.
  3. Create a hard link from settings.dat.LOG1 to C:\Windows\win.ini.
  4. Execute the start ms-paint: command to run Paint 3D.
  5. Terminate Paint 3D processes.
  
  Expected result:
  It isn't possible to overwrite a file not writable by a low privileged user.
  
  Observed result:
  C:\Windows\win.ini file is overwritten with registry data.
  
  References:
  https://github.com/sgabe/CVE-2019-1476
  https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-1476
  https://krbtgt.pw/dacl-permissions-overwrite-privilege-escalation-cve-2019-0841
  

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