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Date: Mon, 8 May 2017 20:32:21 +0200
From: Florian Weimer <fweimer@...hat.com>
To: oss-security@...ts.openwall.com, Salvatore Bonaccorso <carnil@...ian.org>
Subject: Re: rpcbomb: remote rpcbind denial-of-service

On 05/07/2017 08:47 PM, Salvatore Bonaccorso wrote:
> Hi
> 
> On Fri, May 05, 2017 at 11:52:49AM +0200, Florian Weimer wrote:
>> On 05/05/2017 11:22 AM, Marcus Meissner wrote:
>>> On Wed, May 03, 2017 at 05:55:20PM -0700, Seth Arnold wrote:
>>>> On Wed, May 03, 2017 at 08:55:23PM +0200, Guido Vranken wrote:
>>>>> This vulnerability allows an attacker to allocate any amount of bytes
>>>>> (up to 4 gigabytes per attack) on a remote rpcbind host, and the
>>>>> memory is never freed unless the process crashes or the administrator
>>>>> halts or restarts the rpcbind service.
>>>>> [...]
>>>>> An extensive write-up can be found here:
>>>>> https://guidovranken.wordpress.com/2017/05/03/rpcbomb-remote-rpcbind-denial-of-service-patches/
>>>>>
>>>>> Exploit + patches: https://github.com/guidovranken/rpcbomb/
>>>>
>>>> Hello Guido, nice find. Have CVE numbers been requested for this issue
>>>> yet? Have you investigated if ntirpc is affected too? Much of the code
>>>> looks similar:
>>>>
>>>> http://sources.debian.net/src/ntirpc/1.4.3-3/src/rpc_generic.c/#L728
>>>
>>> We also saw glibc affected.
>>>
>>> https://bugzilla.suse.com/show_bug.cgi?id=1037559#c7
>>>
>>> That said, your reproducer allocates virtual memory, and on systems with overcommit
>>> there is only neglible impact on overall memory pressure.
>>>
>>> The rpc service will however likely crash at some point though when there is no virtual
>>> address space left for it.
>>
>> Thanks, I filed it upstream as well:
>>
>> https://sourceware.org/bugzilla/show_bug.cgi?id=21461
>>
>> Looks like both xdr_bytes and xdr_string have a similar bug.
>>
>> I'd appreciate some guidance on reusing or not reusing CVE IDs here.
> 
> A separate CVE should be used for this issue as clarified with MITRE.
> 
> It was assigned CVE-2017-8804.
> 
> https://sourceware.org/bugzilla/show_bug.cgi?id=21461
> 
> Patch posted at
> https://sourceware.org/ml/libc-alpha/2017-05/msg00105.html by Florian
> Weimer.

Note that we have a bit of a dispute here whether whether this is 
actually a vulnerability in the XDR code, or whether the caller is to blame.

Thanks,
Florian

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