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Date: Sun, 5 Sep 2010 21:47:00 -0700
From: Valient Gough <valient@...il.com>
To: oss-security <oss-security@...ts.openwall.com>
Cc: "Steven M. Christey" <coley@...us.mitre.org>,
 Micha Riser <micha@...world.org>
Subject: Re: CVE Request -- EncFS / fuse-encfs [three ids] -- Multiple Vulnerabilities in EncFS


On Sep 5, 2010, at 11:33 AM, Jan Lieskovsky wrote:

> Hello Steve, vendors,
> 
>  Micha Riser reported:
>  [A] http://archives.neohapsis.com/archives/fulldisclosure/2010-08/0316.html
> 
> three security flaws in EncFS encrypted filesystem (more from [A]):
> 
> "A security analysis of EncFS has revealed multiple vulnerabilities:
> (1) Only 32 bit of file IV used
> (2) Watermarking attack
> (3) Last block with single byte is insecure"
> 
> References:
>  [B] http://www.arg0.net/encfs
>  [C] http://bugs.gentoo.org/show_bug.cgi?id=335938
>  [D] http://archives.neohapsis.com/archives/fulldisclosure/2010-08/att-0316/watermark-attack-encfs.tar.gz
>  [E] https://bugzilla.redhat.com/show_bug.cgi?id=630460
> 
> 
> Solutions / patches information:
> ================================
> 
> * for issue (1) -- seems it wasn't fixed / isn't possible to
>  fix without breaking backward compatibility. More from [B]:
> 
>  "The old IV setup is kept for backwards compatibility."
> 
> * for issue (2) -- EncFS upstream has released a fix for the issue:
>  [F] http://code.google.com/p/encfs/source/detail?r=59
> 
> Valient, could you please confirm, the above referenced [F] patch,
> is the correct one to address the watermarking attack issue?
> 
> * for issue (3) -- not sure about patch status (included in [F] too?)
> 

Jan,

Yes, the patch referenced in [F],  specifically changes to SSL_Cipher.cpp, were made in response to issues (1) & (2).  These are not backward compatible, and so only apply to new filesystems.

Issue (3) is not directly addressed.  A workaround is to enable per-block MAC headers, or per-block random bytes.  A patch going into 1.7.2 allows per-block random bytes to be configured independently of MAC headers.  It would be possible to change the default settings such that per-block random bytes are always used.

Adding new encryption modes is not planned for encfs 1.x.

regards,
Valient



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