I was recently asked about how to prevent SQL injection attacks from CGI form variables. My answer was 'placeholders' -- I haven't written SQL without placeholders in about eight years. Placeholders are part of my standard toolbox.

Anything else? I was asked. Puzzled, I thought about it, then added #!/usr/bin/perl -Tw at the top of the white board, turning on taint-checking for the entire script. Anything more? Nope -- I had no more ideas.

You need to run the form data through a regex to sanitize it, I was told. Yes, someone else added -- some of the DBD modules don't do a very good job of 'quoting' the data values.

I admit I haven't spent a lot of time digging through the DBD modules to find out exactly how they do their job, but I've assumed that it was a safe enough practice to use just placeholders to prevent SQL injection attacks.

Comments? Thoughts? DBD modules that might be suspect?

Update: I've posted an update where I try to do an SQL injection into MySQL, PostgreSQL and SQLite database tables using placeholders. All three attempts fail.

Alex / talexb / Toronto

"Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds

In reply to Preventing SQL injection attacks: are -T and placeholders not enough? by talexb

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