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Date: Sat, 15 Nov 2014 12:17:49 -0800
From: Michal Zalewski <>
To: oss-security <>
Subject: Re: Re: strings / libbfd crasher

> OTOH the "most" part in "most compression utilities" is somewhat
> questionable. There are quite a number of them. E.g. File Roller supports
> arj, lha, zoo...

Sure, I mean, the stuff people normally download and click on without
hesitation (tar, gz, zip, xz, 7z). There are hundreds of less common
tools and libraries that are probably awful.

>> The default operation of
>> /usr/bin/strings and the way many people ended up using it arguably
>> violates that assumption in a particularly pronounced way. Tools such
>> as objdump are a bit of a grey area, too.
> Why is that? I think using objdump to analyze malware is quite common.

Oh, I meant that it's still a bit sketchy (maybe less than 'strings'
because the untrusted input use case is a lot more specialized and
fewer people are at risk).

>> [...tcpdump...]
> Not good. Haven't you looked into it -- are these crashes due to malformed
> pcap format or due to malformed traffic?

Both, IIRC. There are some test cases that come with afl-fuzz.

> BTW any crash in imagemagick during image processing is regarded as a
> security issue? Probably a grateful target for fuzzing.

Well... probably? For example, some sites use ImageMagick to convert /
resize user-uploaded images. One would hope that they check file
headers and only accept JPEG / GIF / PNG or so, but that's probably
not universally true.

>> Now, the quality of the *average* OSS project is probably comparable
>> to libbfd, but the average OSS project is probably less likely to be
>> exposed to untrusted inputs under normal operating conditions.
> Sorry, I don't understand your stance. There is a whole world of desktop
> tools and applications -- from `file` and `strings` to LibreOffice and
> Blender. And most of them process files received from untrusted sources.

I wouldn't describe LibreOffice as a typical example. It's obviously
security-critical. What I mean is that, across all the packages
installed on your system, most bugs are fairly irrelevant from the
security perspective - i.e., it probably doesn't matter if you can
crash uname or ps by passing AAAAAAA... in the command line.


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