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Date: Tue, 12 Aug 2014 22:04:28 -0700
From: Andy Lutomirski <>
Subject: Re: CVE Request: ro bind mount bypass using user namespaces

On Tue, Aug 12, 2014 at 4:54 PM, Andy Lutomirski <> wrote:
> On 08/12/2014 02:48 PM, Kenton Varda wrote:
>> Due to a bug in the Linux kernel's implementation of remount, on systems
>> with unprivileged user namespaces enabled, it is possible for an
>> unprivileged user to gain write access to any visible read-only bind mount.
>> It is also possible to bypass flags like nodev, nosuid, and noexec.
>> This problem affects sandboxing / containerization systems that do not
>> expose the regular filesystem to the sandboxed process, but do expose a
>> bind-mounted view of that filesystem using these flags to enforce security.
>> This bug may enable a sandbox break-out. Sandboxes which have used
>> seccomp-bpf to disable the "mount" system call or to disable user
>> namespaces are likely safe.
> nosuid/nodev failures are probably exploitable for full root in many
> common configurations.

Yup.  I have a fairly reliable exploit now.  Will post the code in a
couple of weeks.


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