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Date:      2 Apr 2000 18:45:36 +0200
From:      naddy@mips.rhein-neckar.de (Christian Weisgerber)
To:        freebsd-questions@freebsd.org
Subject:   Re: Lynx forbidden
Message-ID:  <8c7tfg$17jv$1@bigeye.rhein-neckar.de>
References:  <20000402024251.A3917@kagan.quedawg.com> <NDBBKMNOJKJGAEKJNLIAIEIPDDAA.dpoland@execpc.com>

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Doug Poland <dpoland@execpc.com> wrote:

> How does a cracker exploit (or create?) buffer overflows 
> that makes lynx vulnerable?  

Exploitation would take the form of somebody having a web site with
overlong URLs (and possibly some other structures lynx is vulnerable
to, I don't know the details of the security audit) that will
overflow lynx' internal buffers, clobber the stack, and cause this
remote data to be executed as code.

Effectively, you would attempt to load a page and unwittingly
execute some code provided from the malicious server locally on
your system under your user ID and permissions.

The possibilities for abuse are immense. Examples include deleting
all your files, modifying your .rhosts or ssh configuration in such
a way as to open up your account to unauthorized remote login, or
copying (possibly sensitive) personal data.

> If I have lynx on my system, when am I at risk?  

When you access a remote untrusted web server.
Please note that the security status of other browsers such as w3m
is more along the lines of "unknown" rather than "safe". And I
don't even want to think about netscape.

> Doesn't sysinstall use lynx to read on-line documentation?
> If it's so risky, why would the installation program use it?

The recognition that lynx is unsafe is somewhat new, and the problem
will probably be fixed eventually. Also, there is no security risk
involved in using it to read the locally installed documentation.

-- 
Christian "naddy" Weisgerber                  naddy@mips.rhein-neckar.de



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