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Date: Wed, 19 Nov 2014 16:24:10 -0800
From: Andy Lutomirski <>
Subject: Re: Linux user namespaces can bypass group-based restrictions

On 11/17/2014 10:43 AM, Andy Lutomirski wrote:
> This is a heads-up, as there is no fix right now.
> On Linux, if you can unshare your user namespace (which is the case on
> many distributions), then you can map your fsuid and fsgid into the
> new namespace and, inside that namespace, drop all of your other
> groups.
> This may allow you to access files protected by POSIX ACLs as "other",
> even if the ACL should have prohibited it based on one of your
> supplementary group IDs.
> This does not appear to allow you to violate negative sudoers
> group entries and the like, since sudo(8) would be confined to the
> user namespace as well and will therefore not gain privilege.
> To those who care about credit: this was discovered by some
> combination of me, Theodore Ts'o, Eric Biederman, Alan Cox, and Casey
> Schaufler.
> See here for some more discussion:
> Disabling CONFIG_USER_NS works around this issue.

Does this need a CVE?  Fedora and Ubuntu are likely to be affected in
their default configurations.  I don't know about the other distributions.


> --Andy

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