Web Application Security
Re: SQLi with backslash Jun 26 2011 08:33AM
Robin Wood (robin digininja org) (1 replies)
On 26 June 2011 06:02, Voulnet <voulnet (at) gmail (dot) com [email concealed]> wrote:
> Yeah, I understood from you that the web app removes only the single
> and double quotes.
>
> So what kind of query would be executed on MySQL? is it:
> 1- insert into log values ('a','b');
> or
> 2- insert into log values (a,b); <-- I doubt it is this way, because a
> and b should be strings.
>
> so if you only add a backslash, which as I understand doesn't get
> stripped, wouldn't the query executed on MySQL be:
>  insert into log values ('a\','b'); <-- which should do the backslash trick?
>
> If that doesn't happen, then you've got a really annoying web app to
> test, haha. Tell them all the O'Rielly's in the world hate them.

It is the second one of your pair but I can only inject into the
second parameter, it is logging a username when attempting to login
and I've no control over the first parameter.

I think we are going to come to the conclusion that I expected, their
coding is bad but they've got away with it.

Robin

>
> On Sun, Jun 26, 2011 at 1:46 AM, Robin Wood <robin (at) digininja (dot) org [email concealed]> wrote:
>> On 25 June 2011 23:40, Voulnet <voulnet (at) gmail (dot) com [email concealed]> wrote:
>>> Have you tried a backslash to let MySQL auto escape a single quote for you?
>>
>> All single and double quotes are being stripped by the application
>> before getting to the SQL query.
>>
>> Nice try though.
>>
>> Robin
>>
>>> Example:
>>>
>>> insert into log values('a\', ' );drop table log --');
>>>
>>> If I am correct, the first parameter would be 'a\', ' <-- this would
>>> be because with the backslash, MySQL would escape the next single
>>> quote, and consider the starting single quote of the 2nd parameter as
>>> the closing quote of the 1st parameter, then what you input as the 2nd
>>> parameter would be executed, so you terminate the insert correctly and
>>> execute your SQLi string.
>>>
>>> I am not sure if it would work, but I'm sure you can play around with
>>> that concept and get it to to work. You might have some lack finding
>>> column truncation issues, too.
>>>
>>> ---------------------------------------------------------
>>> Voulnet: Your local geek
>>> Stalk me on twitter @Voulnet
>>>
>>>
>>> On Sat, Jun 25, 2011 at 10:33 PM, Robin Wood <robin (at) digininja (dot) org [email concealed]> wrote:
>>>> On 25 June 2011 17:51, Voulnet <voulnet (at) gmail (dot) com [email concealed]> wrote:
>>>>> Okay then, have you tried an alternate encoding? MySQL can act funny
>>>>> when asian characters are used. For reference you can see this:
>>>>>
>>>>> http://stackoverflow.com/questions/1220182/does-mysql-real-escape-string
-fully-protect-against-sql-injection
>>>>>
>>>>> Because, if I understand correctly, there would a discrepancy between
>>>>> what PHP sees (thinking it is a normal multibyte character and passing
>>>>> it on, and what MySQL sees if set incorrectly which would result in it
>>>>> parsing the asian character as something + single quote.
>>>>
>>>> Just tried and it didn't work, was worth a try.
>>>>
>>>>> By the way, have you tried the char(39) or hex encoding and verified
>>>>> it didn't work?
>>>>
>>>> Yes, it won't work as the char(39) is inside the quotes so is just
>>>> taken as a string:
>>>>
>>>> insert into log values ('a', 'xx char(39) ...');
>>>>
>>>> To use it I would have to have broken out of the quotes first.
>>>>
>>>> Robin
>>>>
>>>>>
>>>>> On Sat, Jun 25, 2011 at 1:36 PM, Robin Wood <robin (at) digininja (dot) org [email concealed]> wrote:
>>>>>> On 24 June 2011 18:17, Voulnet <voulnet (at) gmail (dot) com [email concealed]> wrote:
>>>>>>> They are probably using that mysql_real_escape_string php function,
>>>>>>> which escapes these characters. There are many ways to bypass it, and
>>>>>>> you can find it all over the web.
>>>>>>>
>>>>>>> Some examples:
>>>>>>>
>>>>>>> use char(39) <-- ASCII decimal value of ' is 39
>>>>>>> or use the hex value. For example SELECT (0x27) <-- 27 is the hex value of '.
>>>>>>>
>>>>>>> For example if you want to load a file, you would call
>>>>>>> load_file('myfile'), using hex encoding you take 'myfile' with the
>>>>>>> single quotes included and convert it to hex, then write it as
>>>>>>> load_file(0x27..........27) with the rest of the hex values of the
>>>>>>> filename characters filled in between.
>>>>>>>
>>>>>>
>>>>>> No, all they are doing is stripping ' and ", they dump the statements
>>>>>> to screen in the error message.
>>>>>>
>>>>>> And using 0x27 will just end up with the string 0x27 being inserted as
>>>>>> it is inside the single quoted string. That might help if I could
>>>>>> escape the quotes but that is the bit I can't do.
>>>>>>
>>>>>> Robin
>>>>>>
>>>>>>>
>>>>>>> On Wed, Jun 22, 2011 at 5:03 PM, Robin Wood <robin (at) digininja (dot) org [email concealed]> wrote:
>>>>>>>> Hi
>>>>>>>> I've got a scenario where both single and double quotes are being
>>>>>>>> stripped but no other escaping appears to be being performed. The
>>>>>>>> database is MySQL with php on top.
>>>>>>>>
>>>>>>>> The query that I've found SQL injection on is in the form
>>>>>>>>
>>>>>>>> insert into log values ('a', 'b');
>>>>>>>>
>>>>>>>> where I can inject in to the second parameter.
>>>>>>>>
>>>>>>>> If I inject a backslash then I get
>>>>>>>>
>>>>>>>> insert into log values ('a', 'b\');
>>>>>>>>
>>>>>>>> which gives an invalid SQL statement and is how the injection was
>>>>>>>> found. Can anyone come up with a way to exploit this? If I put
>>>>>>>> anything before the slash isn't really worth anything and if I put
>>>>>>>> anything after then the statement becomes valid and the slash escapes
>>>>>>>> whatever character is after it.
>>>>>>>>
>>>>>>>> I thought about using the slash to encode something but couldn't get it to work.
>>>>>>>>
>>>>>>>> The table is write only for me, I can't see any of its entries echo'ed
>>>>>>>> back to the site anywhere so I can't go for stored XSS or anything
>>>>>>>> like that (maybe possible but not in the time available for the test).
>>>>>>>>
>>>>>>>> Apart from breaking the statement I can't see a way to exploit this,
>>>>>>>> can anyone else?
>>>>>>>>
>>>>>>>> Robin
>>>>>>>>
>>>>>>>>
>>>>>>>>
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>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>

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[ reply ]
Re: SQLi with backslash Jun 26 2011 05:29PM
Voulnet (voulnet gmail com)


 

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