Date: Wed, 19 Nov 2014 16:24:10 -0800 From: Andy Lutomirski <luto@...capital.net> To: oss-security@...ts.openwall.com 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: > http://thread.gmane.org/gmane.linux.man/7385/ > > 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 > > --Andy >
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