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Re: Windows Platform Binary Table (WPBT) - BIOS PE backdoor



Some more info

https://www.us-cert.gov/ncas/current-activity/2015/08/12/Lenovo-Service-Engine-LSE-BIOS-Vulnerability


2015-08-12 14:44 GMT+03:00 Kevin Beaumont <kevin.beaumont@xxxxxxxxx>:
> PRECURSOR
>
> There will be debate about if this is a vulnerability.  It affects a
> majority of user PCs -- including all Enterprise editions of Windows,
> there is no way to disable it, and allows direct code execution into
> secure boot sequences.  I believe it is worth discussing.
>
> SCOPE
>
> Microsoft documented a feature in Windows 8 and above called Windows
> Platform Binary Table.  Up until two days ago, this was a single Word
> document not referenced elsewhere on Google:
>
>  http://webcache.googleusercontent.com/search?q=cache:H-SSYRAB0usJ:download.microsoft.com/download/8/A/2/8A2FB72D-9B96-4E2D-A559-4A27CF905A80/windows-platform-binary-table.docx+&cd=1&hl=en&ct=clnk&gl=us
>
> This feature allows a BIOS to deliver the payload of an executable,
> which is run in memory, silently, each time a system is booted.  The
> executable code is run under under Session Manager context (i.e.
> SYSTEM).
>
> This technique is being used by Lenovo and HP to silently deliver
> software, even after systems are completely wiped.  This issue came to
> light in this forum thread:
> http://arstechnica.com/civis/viewtopic.php?p=29551819#p29551819
>
> Additionally, the code is injected and executed in Windows after the
> Windows kernel has booted - meaning hard drives are accessible.  In a
> HP document - http://h10032.www1.hp.com/ctg/Manual/c03857419.pdf page
> 18 - they reference they use Windows Platform Binary Table to inject
> their code into encrypted systems (e.g. BitLocker) (!!!!).
>
> MITIGATIONS
>
> It is not possible to disable this functionality.  If you can gain
> access to the BIOS, you can inject code into the Windows boot sequence
> using the documentation linked above.  The BIOS delivered PE code is
> not countersigned by Microsoft.
>
> Microsoft say: "If partners intentionally or unintentionally introduce
> malware or unwanted software though the WPBT, Microsoft may remove
> such software through the use of antimalware software.  Software that
> is determined to be malicious may be subject to immediate removal
> without notice."
>
> However, you are relying on Microsoft being aware of attacks.  Since
> the code is executed in memory and not written to disk prior to
> activation, Windows Defender does not even scan the executed code.