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Watching SO come online has been quite an education for me. I'd like to make a checklist of various vunerabilities and exploits used against web sites, and what programming techniques can be used to defend against them.

  • What categories of vunerabilities?
  • What kind of defensive programming techniques?
  • etc...
Yeldar Kurmangaliyev
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Mark Harrison
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9 Answers9

12

From the Open Web Application Security Project:

  1. The OWASP Top Ten vulnerabilities (pdf)
  2. For a more painfully exhaustive list: Category:Vulnerability

The top ten are:

  1. Cross-site scripting (XSS)
  2. Injection flaws (SQL injection, script injection)
  3. Malicious file execution
  4. Insecure direct object reference
  5. Cross-site request forgery (XSRF)
  6. Information leakage and improper error handling
  7. Broken authentication and session management
  8. Insecure cryptographic storage
  9. Insecure communications
  10. Failure to restrict URL access
Charles Miller
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6

I second the OWASP info as being a valuable resource. The following may be of interest as well, notably the attack patterns:

David Schlosnagle
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Obviously test every field for vulnerabilities:

  • SQL - escape strings (e.g. mysql_real_escape_string)
  • XSS
  • HTML being printed from input fields (a good sign of XSS usually)
  • Anything else thatis not the specific purpose that field was created for

Search for infinite loops (the only indirect thing (if a lot of people found it accidentally) that could kill a server really).

Ross
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2

Some prevention techniques:

XSS

  • If you take any parameters/input from the user and ever plan on outputting it, whether in a log or a web page, sanitize it (strip/escape anything resembling HTML, quotes, javascript...) If you print the current URI of a page within itself, sanitize! Even printing PHP_SELF, for example, is unsafe. Sanitize! Reflective XSS comes mostly from unsanitized page parameters.

  • If you take any input from the user and save it or print it, warn them if anything dangerous/invalid is detected and have them re-input. an IDS is good for detection (such as PHPIDS.) Then sanitize before storage/printing. Then when you print something from storage/database, sanitize again! Input -> IDS/sanitize -> store -> sanitize -> output

  • use a code scanner during development to help spot potentially vulnerable code.

XSRF

  • Never use GET request for destructive functionality, i.e. deleting a post. Instead, only accept POST requests. GET makes it extra easy for hackery.
  • Checking the referrer to make sure the request came from your site does not work. It's not hard to spoof the referrer.
  • Use a random hash as a token that must be present and valid in every request, and that will expire after a while. Print the token in a hidden form field and check it on the server side when the form is posted. Bad guys would have to supply the correct token in order to forge a request, and if they managed to get the real token, it would need to be before it expired.

SQL injection

  • your ORM or db abstraction class should have sanitizing methods - use them, always. If you're not using an ORM or db abstraction class... you should be.
Zach
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SQL injection

coder1
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XSS (Cross Site Scripting) Attacks

Bernie Perez
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Easy to oversee and easy to fix: the sanitizing of data received from the client side. Checking for things such as ';' can help in preventing malicious code being injected into your application.

jwarzech
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G'day,

A good static analysis tool for security is FlawFinder written by David Wheeler. It does a good job looking for various security exploits,

However, it doesn't replace having a knowledgable someone read through your code. As David says on his web page, "A fool with a tool is still a fool!"

HTH.

cheers, Rob

Rob Wells
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You can get good firefox addons to test multiple flaws and vulnerabilities like xss and sql injections from Security Compass. Too bad they doesn't work on firefox 3.0. I hope that those will be updated soon.

Vertigo
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