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Re: out of bounds stack access in idn tool

From: Simon Josefsson
Subject: Re: out of bounds stack access in idn tool
Date: Sun, 12 Jul 2015 17:20:04 +0200
User-agent: Gnus/5.130014 (Ma Gnus v0.14) Emacs/24.4 (gnu/linux)

Hanno Böck <address@hidden> writes:

> Hi,
> When passing the attacked file (libidn-oob-stack-read-main) to the idn
> command line tool this will cause an out of bounds stack access. This
> can be seen with either valgrind or by recompiling idn with address
> sanitizer. The input consists of a random character, a newline and a
> zero byte.
> The error happens in the function main in this code
>       if (readbuf[strlen (readbuf) - 1] == '\n')
>       readbuf[strlen (readbuf) - 1] = '\0';
> If readbuf is a zero byte string this won't work. I have attached a
> patch how to prevent this. Not sure if this is the best way, but it
> prevents the oob access.

Thank you for the report.  I believe idn should use getline instead of
this funky fixed-buffer fgets+hacks approach.  I'll try to implement it.


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