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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT Security Bulletin ASB-2021.0159.3 Windows Elevation of Privilege Vulnerability 13 August 2021 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Microsoft Windows Operating System: Windows Impact/Access: Execute Arbitrary Code/Commands -- Existing Account Administrator Compromise -- Existing Account Resolution: Mitigation CVE Names: CVE-2021-36934 Revision History: August 13 2021: Microsoft updated advisory with security update details July 23 2021: Microsoft added additonal Windows versions and information on how to delete shadow copies July 21 2021: Initial Release OVERVIEW Microsoft has released an out of band advisory for a Windows elevation of privilege vulnerability. Microsoft has assigned CVE-2021-36934 to this vulnerability [1] IMPACT Microsoft states that "An elevation of privilege vulnerability exists because of overly permissive Access Control Lists (ACLs) on multiple system files, including the Security Accounts Manager (SAM) database. An attacker who successfully exploited this vulnerability could run arbitrary code with SYSTEM privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. An attacker must have the ability to execute code on a victim system to exploit this vulnerability." [1] Microsoft currently advises that this issue affects Windows 10 versions 1809 and newer. [1] ========UPDATE 23/07/2021========= Microsoft added additional affected Windows versions. These include Windows Server 2004, Windows Server 2019 and Windows Server version 20H2 [1] MITIGATION There is currently no patch available for this vulnerability, Microsoft have provided the following workaround: "Restrict access to the contents of %windir%\system32\config 1. Open Command Prompt or Windows PowerShell as an administrator. 2. Run this command: icacls %windir%\system32\config\*.*/inheritance:e Delete Volume Shadow Copy Service (VSS) shadow copies 1. Delete any System Restore points and Shadow volumes that existed prior to restricting access to %windir%\system32\config. 2. Create a new System Restore point (if desired). Impact of workaround Deleting shadow copies could impact restore operations, including the ability to restore data with third-party backup applications. Note You must restrict access and delete shadow copies to prevent exploitation of this vulnerability." [1] Microsoft will update the CVE as their investigation progresses. [1] ========UPDATE 23/07/2021========= Microsoft added a link to KB5005357 which provides information on how to delete shadow copies. [2] ========UPDATE 13/08/2021========= Microsoft updated advisory on August 10, 2021 to announce it is releasing security updates for all affected versions of Windows to address this vulnerability. [1] REFERENCES [1] Windows Elevation of Privilege Vulnerability https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-36934 [2] KB5005357- Delete Volume Shadow Copies https://support.microsoft.com/en-gb/topic/kb5005357-delete-volume-shadow-copies-1ceaa637-aaa3-4b58-a48b-baf72a2fa9e7 AusCERT has made every effort to ensure that the information contained in this document is accurate. However, the decision to use the information described is the responsibility of each user or organisation. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. AusCERT takes no responsibility for consequences which may arise from following or acting on information or advice contained in this security bulletin. =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQIVAwUBYRYP2ONLKJtyKPYoAQiGbQ//aBIBEzoDcSmDTl1TB+3LO4Mvxs366L4b +PrZ3dxLgWPeVKYRVqoEDyRp2GJh7dAreklZb1RZT67KK4+LMQlmh312QZq4IrAy avufPmzXfk1XTM5vFTu+1oQ+3SGMNc3q7+6Np5mFx7/lhAcTW+SC68YQFtqywakD im91gBTZNTdZxi7GyMnY9mnyMAOtSYuN5/+kzE5X3BeIxl731WnzNMHkUYRRKdyD XwkZHUSeFLAEN/D3oQ2T5fY6DxgqoFs5zdxI6xcmh/omxynRMGuk/SNPlMTe2a7o wLc+GpyuwbQRrSVY3R5hkRGnyF6ZJo5a0vdOySHYc+IHCXmByG45g3fukh5pUrY3 OuNHmvS11gXBZFp74T9vNtnaMy7nUbQNKJMCf/KmCdJHoLAFxBaEt71bEY1robNz 2pA/dDha1dTwJ0VVlV5sRreaHM21J/OKpTGI6Ob/elntLMTU5pBpd8kDEG32MYRD sI8nM/QKrETPmmiMYsG6olIDttFs8yr2LCruI84fo5cnQFIuFRwqJplfFql5Coao d22KeoLUevmMszOmoTfEUnG4Ds7GUs4O/zximm78VtHHA1Rt8DVxhwjSPCqzFLnA orZ1mveEUIUU9x0JW0BihryvtCYvhCpMIDLTuMk2DVkBl750ROklFIYmbmer3Zrt +3W2ird5Ox4= =QXWr -----END PGP SIGNATURE-----