Re: [PWNED/DOSSED] Cygwin's setup-x86.exe loads and executes rogue DLL from its application directory

[Yucong Sun <sunyucong at gmail dot com>]

Your emails could have been clearer , in any case, it seems the
easy/right solution is to add

SetDefaultDllDirectories(LOAD_LIBRARY_SEARCH_SYSTEM32)

to the exe?

On Wed, Jan 6, 2016 at 10:17 PM, Stefan Kanthak <stefan.kanthak@nexgo.de> wrote:
> Second and last chance!
> See <http://home.arcor.de/skanthak/policy.html>
>
> ----- Original Message -----
> From: "Stefan Kanthak" <stefan.kanthak@nexgo.de>
> To: <security@cygwin.org>
> Cc: <security@redhat.com>
> Sent: Monday, December 28, 2015 4:23 AM
> Subject: [PWNED/DOSSED] Cygwin's setup-x86.exe loads and executes rogue DLL from its application directory
>
>
>> Hi,
>>
>> Cygwin's setup-x86.exe loads and executes UXTheme.dll
>> (on Windows XP also ClbCatQ.dll) and more from its
>> "application directory".
>>
>> For software downloaded with a web browser the application
>> directory is typically the user's "Downloads" directory: see
>> <https://insights.sei.cmu.edu/cert/2008/09/carpet-bombing-and-directory-poisoning.html>,
>> <http://blog.acrossecurity.com/2012/02/downloads-folder-binary-planting.html>
>> and <http://seclists.org/fulldisclosure/2012/Aug/134>
>>
>> If UXTheme.dll (or one of the other DLLs) gets planted in
>> the user's "Downloads" directory per "drive-by download" or
>> "social engineering" this vulnerability becomes a remote code
>> execution.
>>
>> If setup-x86.exe is NOT started with --no-admin the vulnerability
>> results in an escalation of privilege too!
>>
>>
>> Proof of concept/demonstration:
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> 1. visit <http://home.arcor.de/skanthak/sentinel.html>, download
>>   <http://home.arcor.de/skanthak/download/SENTINEL.DLL> and save
>>   it as UXTheme.dll in your "Downloads" directory;
>>
>> 2. on Windows XP, copy the downloaded UXTheme.dll as ClbCatQ.dll;
>>
>> 3. download setup-x86.exe and save it in your "Downloads" directory;
>>
>> 4. execute setup-x86.exe from your "Downloads" directory;
>>
>> 5. notice the message boxes displayed from UXTheme.dll placed in
>>   step 1 (and ClbCatQ.dll placed in step 2).
>>
>> PWNED!
>>
>> 6. copy the downloaded UXTheme.dll as WSock32.dll (on Windows XP
>>   also as PSAPI.dll and WS2_32.dll);
>>
>> 7. rerun setup-x86.exe from your "Downloads" directory.
>>
>> DOSSED!
>>
>> 8. turning the denial of service into an arbitrary (remote) code
>>   execution is trivial: just add the SINGLE entry (PSAPI.dll:
>>   EnumProcesses, WSock32.Dll: recv, WS2_32.dll: Ordinal 21)
>>   referenced from setup-x86.exe to a rogue DLL of your choice.
>>
>> PWNED again!
>>
>>
>> See <http://seclists.org/fulldisclosure/2015/Nov/101>,
>> <http://seclists.org/fulldisclosure/2015/Dec/86> and
>> <http://seclists.org/fulldisclosure/2015/Dec/121> plus
>> <http://home.arcor.de/skanthak/!execute.html> and
>> <http://home.arcor.de/skanthak/sentinel.html> for details about
>> this well-known and well-documented BEGINNER'S error!
>>
>>
>> Then dump your vulnerable executable installer and provide a SAFE
>> installer instead: either .MSI or .INF (plus .CAB).
>>
>>
>> I'll publish in 45 days.
>> See <http://home.arcor.de/skanthak/policy.html> and return the
>> CVE identifier assigned for this vulnerability to me!
>>
>>
>> regards
>> Stefan Kanthak
>
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