SQL injection/Blind/Extraction/Precomputation

The comparative precomputation attack

This attack relies heavily on the remote dataset for successful exploitation and is thus less reliable than other methods. This significantly differs from previously discovered single-byte exfiltration techniques because:

It is based on precomputation It is not a timing attack

Requirements: The query which is being injecting into must have at least 254 rows The precomputation attack is compatible with all database backends.

Precomputation is done for performance reasons. At the very least, a comparative test will be required. The more complex a remote site is (random content generation, etc), the more difficult this type of attack becomes to automate.

Examining the following query: $query = "select * from articles where id=$input"; And the following uri: /articles.php?id=1 Testing can be used to see if there are 255 articles by visiting: /articles.php?id=255 Follow the next steps for automation (and sanity's) sake: Choose a language supporting something similar to array_flip() for programming the automation tool. Write a loop to download each article In the loop, populate an array (using integer indexes) with checksum hashes as values Flip the array Almost done! Then the following visit can take place: /articles.php?id=ascii(substr(user(),1,1)) Checksum the output Now accessing the checksums array using the checksum of the output as the key: $ascii_code = $checksums[$output_checksum]; And the value of a byte has been determined. Protip: This attack can be extended by: Using arithmetic operators to get sequential id's offset from 0-255 (e.g. /articles.php?id=(select ascii(substr(user(),1,1))+67) Using MySQL field operators and a static query that returns id's to bypass the requirement for the id's to be sequential