Re: [FFmpeg-devel] [PATCH v10 1/2] avformat/imf: Demuxer

From: Lynne <dev@lynne.ee>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH v10 1/2] avformat/imf: Demuxer
Date: Fri, 17 Dec 2021 21:54:14 +0100 (CET)
Message-ID: <Mr9A74---3-2@lynne.ee> (raw)
In-Reply-To: <163975114109.13029.10142418833883066194@lain.red.khirnov.net>

Dec 17, 2021, 3:25 PM by anton@khirnov.net:

> Quoting Pierre-Anthony Lemieux (2021-12-15 21:41:25)
>
>> On Wed, Dec 15, 2021 at 12:20 PM Anton Khirnov <anton@khirnov.net> wrote:
>> >
>> > Quoting Pierre-Anthony Lemieux (2021-12-15 01:17:26)
>> > > >
>> > > > Now the question is whether a malicious attacker can craft those two
>> > > > files to get access to anything they shouldn't. I suppose at the very
>> > > > least the attacker can get information that the user opened the file (by
>> > > > adding an asset on an attacker's server) but that will be a danger with
>> > > > any playlists allowing network resources and can be controlled with
>> > > > io_open(). Can you think of any other possible issues?
>> > > >
>> > >
>> > > Some security considerations:
>> > >
>> > > - a DDoS can conceivably occur if a malicious CPL+ASSETMAP is widely
>> > > distributed. Both an ASSETMAP and a CPL are required since (a) the CPL
>> > > does not contain paths/hyperlinks and (b) only those resources
>> > > referenced by the CPL are fetched using the ASSETMAP.
>> > > - the CPL uses XML, which has its own security considerations. For
>> > > example, XML parsing can result in entities being fetched over the
>> > > network, but this is disabled by default in libxml AFAIK.
>> >
>> > This is concerning. From a brief glance at libxml2, it seems that you
>> > need to pass XML_PARSE_NONET as the last parameter to xmlReadMemory() to
>> > actually disabling network fetching.
>> > But it is possible I'm misreading the code, so if you or anyone else
>> > understands this better then clarifications are welcome.
>>
>> I was referring to entity expansion and the loading of DTDs being
>> disabled by default -- see XML_PARSE_NOENT and XML_PARSE_DTDLOAD at
>> [1-2].
>>
>
> Okay then. If nobody has further comments, I will push your latest patch
> in a few days.
>

I think this shouldn't get merged into 5.0. It would get minimal amount
of fuzzing if it does now, so let's leave it for a later release?
I'd still like to see libuuid being used, we have several uses for it already.

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