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Date: Sat, 18 Apr 2015 18:27:48 +0200
From: Harald Becker <>
CC: Matt Johnston <>
Subject: Re: Re: Security advisory for musl libc - stack-based buffer
 overflow in ipv6 literal parsing [CVE-2015-1817]

Hi !

@Rich: I still get DNS error (Mozilla Thunderbird) for, 
when tying to send mail :(

On 18.04.2015 17:58, Rich Felker wrote:
> On Sat, Apr 18, 2015 at 05:49:51PM +0200, Harald Becker wrote:
>> On 18.04.2015 17:25, Rich Felker wrote:
>>>> The server hostkey will remain in process memory since it's
>>>> required for rekeying - not as bad as root code execution
>>>> though.
>>> Ugly. I don't see how this can be solved without a more advanced
>>> privsep model. I agree it's lower-severity though.
>> IMO you may put the host keys in a file readable (not writable)
>> with a dropbear group, and only using that group for dropbear (no
>> other users or programs using that group). So you may read the keys
>> even if not root, if you add this dropbear group to setgroups (not
>> setgid) before dropping root privileges.
> The key is already in memory.

As far as I understand it, the question was, *not to have* the key
hanging around in memory, but still have access without requirement to
keep root privileges. My suggestion is to solve this, with a very simple
and easy to implement solution. I consider it a slight increased
security, as the dropbear process can drop root privileges (and has to
do so), but still has access to the host keys.

> A design like the above would not significantly improve security
> (except for heartbleed type issues); it would be just like the
> situation now where the key is already in memory.

ACK, as told it's intention is a simple solution to give dropbear access
to the host keys without letting them hang in memory all the time.

> To make it more secure, the session process would not have any access
> to the key and would have to communicate with an existing privileged
> process to rekey.

ACK, much better, but this would need major restructuring, wouldn't it?

So consider my suggestion a simpler to implement solution, in between 
having full root privileges or hanging keys in memory, and an external 
process to do the rekey steps (in addition: with the possibility to let 
that process use the dropbear group and not root to access keys - even 
better than let that process hang around as root)


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