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<blockquote data-quote="Andy Ful" data-source="post: 957955" data-attributes="member: 32260"><p><strong><span style="font-size: 18px">Simple Windows Hardening vs. advanced attacks.</span></strong></p><p><strong>Microsoft Office exploit CVE-2021-40444</strong></p><p></p><p>This exploit can be seen as an evolution of the MS Office exploitation via abusing OLE/ActiveX. The old attack was based on a payload (CPL file, script, etc.) embedded in the MS Office document. The user was convinced by the attacker to click the icon in the document. This caused to drop of the embedded file (payload) to the user Temp folder and Word requested opening the payload by the OS. For example, the file association for CPL file is defined in the Windows Registry:</p><p></p><p>[ATTACH=full]260591[/ATTACH]</p><p></p><p>At this moment the SRP (used in SWH to block files like CPL, INF, etc.) checks the file path and blocks the file execution.</p><p></p><p>The new exploit does not use the payload embedded in the document body, but uses MSHTML to update the document. Microsoft Word must download a web page, from the URL referenced into the document. The web content uses JavaScript code executed into MSHTML ActiveX component of Microsoft Word - the payloads are dropped/extracted to disk. There is no payload in the document, but still Word requests opening the payload by the OS, so SRP can block it.</p><p></p><p>[ATTACH=full]260593[/ATTACH]</p><p></p><p>The infection chain on the chart is for the version which downloads the payloads from the Internet, but it can be modified to do its work locally.</p><p>The JavaScript code applies the value « <em>.cpl:123</em> » to the « <em>document.URL</em> » parameter. This allows opening the file with any extension (the INF extension was chosen in the wild) as a CPL file.</p><p></p><p>[URL unfurl="true"]https://www.stormshield.com/news/cve-2021-40444-security-alert-the-response-of-stormshield-products/[/URL]</p><p>[URL unfurl="true"]https://www.microsoft.com/security/blog/2021/09/15/analyzing-attacks-that-exploit-the-mshtml-cve-2021-40444-vulnerability/[/URL]</p><p></p><p>Edit</p><p>On September 2021 Patch Tuesday, Microsoft has fixed this exploit.</p></blockquote><p></p>
[QUOTE="Andy Ful, post: 957955, member: 32260"] [B][SIZE=5]Simple Windows Hardening vs. advanced attacks.[/SIZE] Microsoft Office exploit CVE-2021-40444[/B] This exploit can be seen as an evolution of the MS Office exploitation via abusing OLE/ActiveX. The old attack was based on a payload (CPL file, script, etc.) embedded in the MS Office document. The user was convinced by the attacker to click the icon in the document. This caused to drop of the embedded file (payload) to the user Temp folder and Word requested opening the payload by the OS. For example, the file association for CPL file is defined in the Windows Registry: [ATTACH type="full" alt="1631780735306.png"]260591[/ATTACH] At this moment the SRP (used in SWH to block files like CPL, INF, etc.) checks the file path and blocks the file execution. The new exploit does not use the payload embedded in the document body, but uses MSHTML to update the document. Microsoft Word must download a web page, from the URL referenced into the document. The web content uses JavaScript code executed into MSHTML ActiveX component of Microsoft Word - the payloads are dropped/extracted to disk. There is no payload in the document, but still Word requests opening the payload by the OS, so SRP can block it. [ATTACH type="full" alt="1631780841148.png"]260593[/ATTACH] The infection chain on the chart is for the version which downloads the payloads from the Internet, but it can be modified to do its work locally. The JavaScript code applies the value « [I].cpl:123[/I] » to the « [I]document.URL[/I] » parameter. This allows opening the file with any extension (the INF extension was chosen in the wild) as a CPL file. [URL unfurl="true"]https://www.stormshield.com/news/cve-2021-40444-security-alert-the-response-of-stormshield-products/[/URL] [URL unfurl="true"]https://www.microsoft.com/security/blog/2021/09/15/analyzing-attacks-that-exploit-the-mshtml-cve-2021-40444-vulnerability/[/URL] Edit On September 2021 Patch Tuesday, Microsoft has fixed this exploit. [/QUOTE]
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