Microsoft warns of attacks targeting Office documents

Affecting Home windows desktops and servers, the assaults exploit an MSHTML vulnerability by utilizing specifically crafted Microsoft Workplace paperwork.

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Picture: iStock/Simonkolton

Microsoft has raised alarm bells over a brand new cyberattack that is actively concentrating on Home windows customers by exploiting a safety flaw via malicious Workplace paperwork. In a safety replace launched on Tuesday, the software program big described its investigation right into a distant code execution vulnerability in MSHTML that works via specifically crafted Microsoft Workplace paperwork.

SEE: Incident response coverage (TechRepublic Premium)

“MSHTML is a element utilized by myriad purposes on Home windows,” stated Jake Williams, co-founder and CTO at incident response agency BreachQuest. “For those who’ve ever opened an software that seemingly ‘magically’ is aware of your proxy settings, that is probably as a result of it makes use of MSHTML beneath the hood.”

By exploiting this flaw, an attacker might devise a malicious ActiveX management utilized by an Workplace doc that hosts the browser’s rendering engine. The attacker must persuade the consumer to open the malicious doc, probably despatched by way of e-mail. Customers with extra restricted accounts on their computer systems might be much less weak than these with full administrative privileges.

The exploit impacts all present variations of Home windows, together with Home windows 7, 8.1, and 10, in addition to Home windows Server 2008, 2012, 2016, 2019 and 2022.

No patch is but accessible for this exploit. Microsoft stated that after finishing its present investigation, it might both present a safety replace via its month-to-month launch cycle or roll out an out-of-cycle replace. Within the meantime, Microsoft Defender Antivirus and Microsoft Defender for Endpoint each detect and shield in opposition to this vulnerability. Customers of both product ought to make sure that they’re updated.

Additional, Microsoft Workplace by default opens paperwork from the web in Protected View or Software Guard for Workplace, each of which forestall the present assault. Workplace customers ought to ensure that Protected View is enabled. To do that, click on the File menu in any Workplace software and choose Choices. Within the Choices window, go to Belief Middle, click on the button for Belief Middle Settings after which choose Protected View.

In lieu of a patch, Microsoft does have a workaround. As described within the safety advisory, use a textual content editor to create a .REG file with the next strings:

Home windows Registry Editor Model 5.00

[HKEY_LOCAL_MACHINESOFTWAREPoliciesMicrosoftWindowsCurrentVersionInternet SettingsZones]

“1001”=dword:00000003

“1004”=dword:00000003

[HKEY_LOCAL_MACHINESOFTWAREPoliciesMicrosoftWindowsCurrentVersionInternet SettingsZones1]

“1001”=dword:00000003

“1004”=dword:00000003

[HKEY_LOCAL_MACHINESOFTWAREPoliciesMicrosoftWindowsCurrentVersionInternet SettingsZones2]

“1001”=dword:00000003

“1004”=dword:00000003

[HKEY_LOCAL_MACHINESOFTWAREPoliciesMicrosoftWindowsCurrentVersionInternet SettingsZones3]

“1001”=dword:00000003

“1004”=dword:00000003

Save the file with the .reg extension. Double-click it so as to add it to the present Registry.

“The excellent news is that this vulnerability is client-side and requires consumer interplay,” stated Casey Ellis, founder and CTO at cybersecurity platform Bugcrowd. “A patch will likely be accessible quickly. Sadly, that is the tip of the excellent news.”

Ellis cautioned that the exploit complexity seems fairly low, which signifies that attackers can extra readily reap the benefits of it. The impression may be very excessive. And in its weaponized kind, the exploit might be utilized in various kinds of assaults, together with ransomware. Plus, even when a patch turns into accessible, many organizations might fail to use that patch shortly sufficient.

“The constant problem with client-side vulnerabilities like this one is that there are a variety of techniques that should be patched, which implies they keep accessible for exploitation to attackers for fairly a while,” Ellis added.

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