7-Zip & MoW, (Sun, Jul 3rd)

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Version 22.0 of 7-Zip introduces support for the propagation of the Mark-of-Web. This is an Alternate Data Stream with name Zone.Identifier that is added by browsers and email clients on Windows system with NTFS disks, to mark that a file was downloaded from and untrusted source (“The Internet”).

This information can then be used by other programs, to decide how to handle such files. For example, Word will open a document in Protected View (a sandbox) when it has a MoW.

The support added to 7-Zip is “propagation of MoW”: this means that if an archive (ZIP file for example) has a Zone.Identifier ADS, then 7-Zip can also add a Zone.Identifier ADS to each extracted file. This is not done by default, it has to be configured.

For the command-line version of 7-Zip, and option (-snz) has to be used.

And for the GUI version, it has to be configured:

This setting is stored inside the reqistry: HKEY_CURRENT_USERSOFTWARE7-ZipOptions WriteZoneIdExtract

WriteZoneIdExtract is a REG_DWORD, if it is absent (the default) or 0, then the Zone.Identifier ADS is not propagated to the extracted files.

When the value is 1, the Zone.Identifier ADS is propagated to the extracted files.

And when the value is 2 (“For Office files”), then the Zone.Identifier ADS is propagated to the extracted files provided these are Office files.

I did some quick tests to find out how 7-Zip decides that a file is an Office file: the decision is made based on the file extension.

Personally, I will set the setting to propagate for all files.

Didier Stevens
Senior handler
Microsoft MVP

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Reposted from SANS. View original.

Alex Post