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Re: invalid memory access in idna_to_ascii_8z

From: Simon Josefsson
Subject: Re: invalid memory access in idna_to_ascii_8z
Date: Wed, 08 Jul 2015 02:14:14 +0200
User-agent: Gnus/5.130014 (Ma Gnus v0.14) Emacs/24.4 (gnu/linux)

Hi.  I've tried to address the invalid UTF-8 issue when using libidn:;a=commitdiff;h=2e97c2796581c27213962c77f5a8571a598f9a2e

Your thoughts and comments on this is appreciated.  Testing whether this
actually solves your problem is encouraged.

Please read the NEWS blurb for background:

** libidn: stringprep_utf8_to_ucs4 now rejects invalid UTF-8. CVE-2015-2059
This function has always been documented to not validate that the
input UTF-8 string is actually valid UTF-8.  Like the rest of the API,
when you call a function that works on UTF-8 data, you have to pass it
valid UTF-8 data.  Application writers appear to have difficulties
using interfaces designed like that, as bugs triggered by invalid
UTF-8 has been identified in a number of projects (jabberd2, gnutls,
wget, and curl).  While we could introduce a new API to perform UTF-8
validation, so that applications can easily implement the proper
checks, this appear error prone because there is a risk that the check
will be forgotten.  Instead, we took the more radical approach of
modifying the documentation and the implementation of the API.  The
intention is that all functions that accepts UTF-8 data should
validate it before use.  This will solve the problem for applications,
without needing to change them.  This change has the unfortunate
side-effect that Surrogate codes (see section 5.5 of RFC 3454) no
longer trigger the STRINGPREP_CONTAINS_PROHIBITED error code but
instead will trigger the newly introduced STRINGPREP_ICONV_ERROR error
code, as the gnulib/libunistring-based code that we use to test
UTF-8-compliance rejects Surrogate codes.  We hope that this is an
acceptable cost to live with in order to improve application security.
We welcome feedback on this solution, and we are marking this release
as beta rather than stable to signal that we may reconsider this
approach if people disagree.  Reported by several people including
Thijs Alkemade, Gustavo Grieco, Daniel Stenberg, and Nikos


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