full-disclosure - Re: Vim: Insecure Temporary File Creation During Build: Arbitrary Code Execution

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Date: Fri, 25 Jul 2008 03:16:00 +0100
From: "Jan Minář" <rdancer@...ncer.org>
To: "Robert Buchholz" <rbu@...too.org>
Cc: vim-dev@....org, full-disclosure@...ts.grok.org.uk,
	bugtraq@...urityfocus.com, bugs@....org,
	"Steven M. Christey" <coley@...us.mitre.org>
Subject: Re: Vim: Insecure Temporary File Creation During
	Build: Arbitrary Code Execution

2008/7/25 Robert Buchholz <rbu@...too.org>:
> On Friday 18 July 2008, Jan Minář wrote:
> ...
>> 3. Vulnerability
>>
>> During the build process, a temporary file with a predictable name is
>> created in the ``/tmp'' directory.  This code is run when Vim is
>> being build with Python support:
>>
>> src/configure.in:
>>
>>          677         dnl -- we need to examine Python's
>> config/Makefile too 678         dnl    see what the interpreter is
>> built from 679         AC_CACHE_VAL(vi_cv_path_python_plibs,
>>          680         [
>>          681             tmp_mkf="/tmp/Makefile-conf$$"
>>   (1)--> 682             cat ${PYTHON_CONFDIR}/Makefile - <<'eof'
>> >${tmp_mkf} 683 __:
>>          684         @echo "python_MODLIBS='$(MODLIBS)'"
>>          685         @echo "python_LIBS='$(LIBS)'"
>>          686         @echo "python_SYSLIBS='$(SYSLIBS)'"
>>          687         @echo "python_LINKFORSHARED='$(LINKFORSHARED)'"
>>          688 eof
>>          689             dnl -- delete the lines from make about
>> Entering/Leaving directory
>>   (2)--> 690             eval "`cd ${PYTHON_CONFDIR} && make -f
>> ${tmp_mkf} __ | sed '/ directory /d'`"
>>          691             rm -f ${tmp_mkf}
>>
>> The attacker has to create the temporary file
>> ``/tmp/Makefile-conf<PID>'' before it is first written to at (1).  In
>> the time between (1) and (2), arbitrary commands can be written to
>> the file.  They will be executed at (2).
>
> The commands do not have to be written there between (1) and (2), they
> can be in the file long before the ./configure was started -- just
> because the script does care whether it can write to the file at all.
> So unlike stated in the advisory, and in CVE-2008-3294, the issue does
> not involve a race condition if the attacker would choose to create a
> 644 file.

The file gets truncated in (1).  You're wrong, the advisory is right.

HTH
HAND

Jan.
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