CVE-2021-36934 PoC — Windows Elevation of Privilege Vulnerability

Source

https://github.com/VertigoRay/CVE-2021-36934

Associated Vulnerability

Title:Windows Elevation of Privilege Vulnerability (CVE-2021-36934)
Description: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. After installing this security update, you must manually delete all shadow copies of system files, including the SAM database, to fully mitigate this vulnerabilty. Simply installing this security update will not fully mitigate this vulnerability. See <a href="https://support.microsoft.com/topic/1ceaa637-aaa3-4b58-a48b-baf72a2fa9e7">KB5005357- Delete Volume Shadow Copies</a>.

Description

Windows Elevation of Privilege Vulnerability (SeriousSAM)

Readme

[CVE described on MSRC](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-36934).
[Remediated](https://www.dataprise.com/resources/blog/microsoft-windows-10-vss-vulnerability-defense-digest) using ECM (aka SCCM) Config Items:

- See the remediation and Discovery scripts in repo.
- Config Item does a boolean `$false` check for compliance.

# Remediation

In production, we found the need to remediate purge copies other than `ClientAccessible` ones; we've seen `Backup` and `DataVolumeRollback` types that couldn't be *deleted*.
Unfortunately, `vssadmin` cleary states that "only shadow copies that have the `ClientAccessible` type can be deleted."
In order to purge them anyway, we needed to shrink the size of the storage down to the smallest amount allowed (320MB); this will cause Windows to purge the *oversized* shadow copy.
We then bring it back to a normal/unbounded size.

File Snapshot


 [4.0K]  /data/pocs/548ed57e0640a8d2938fd9a45bf3e59d84fa9aa4
├── [ 409]  Discovery.ps1
├── [ 895]  README.md
└── [ 868]  Remediation.ps1

0 directories, 3 files

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