Full Disclosure mailing list archives
Re: [anti-XSS]about CERT/CC:malicious_code_mitigation
From: dd <dd () ghettohackers net>
Date: Mon, 09 Aug 2004 19:45:07 -0700
Woops, O'Brian is pissed again ;)Real solution is to have "per input" input validation which will always let some "potentially bad" things through, but help mitigate exposures and then do things "right". Right of course means always binding data to sql statements and properly performing context sensitive output encoding.
dd Valdis.Kletnieks () vt edu wrote:
On Sat, 07 Aug 2004 06:25:00 -0000, bitlance winter said:#! The first function takes the negative approach. #! Use a list of bad characters to filter the data sub FilterNeg { local( $fd ) = @_; $fd =~ s/[\<\>\"\'\%\;\)\(\&\+]//g; return( $fd ) ; }*BZZT!!* Wrong. Don't do this in production code, because...I have understood that bad characters are < > " ' % ; ) ( & +If it turns out that * (asterisk) is a "bad character", you're screwed. If it turns out that *any other* character is "bad", you're screwed. The *proper* way to do the filtering is to *remove* *all* characters not known to be good. Something like: $fd =~ s/[^-_ a-zA-Z0-9]//g; Only pass alphabetic, numeric, space, hyphen, and underscore. Add other characters *only* if you can show they are *not* a problem.
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Current thread:
- [anti-XSS]about CERT/CC:malicious_code_mitigation bitlance winter (Aug 07)
- Re: [anti-XSS]about CERT/CC:malicious_code_mitigation Valdis . Kletnieks (Aug 09)
- Re: [anti-XSS]about CERT/CC:malicious_code_mitigation dd (Aug 09)
- Re: [anti-XSS]about CERT/CC:malicious_code_mitigation Valdis . Kletnieks (Aug 09)
- Re: [anti-XSS]about CERT/CC:malicious_code_mitigation dd (Aug 09)
- Re: [anti-XSS]about CERT/CC:malicious_code_mitigation Dave Horsfall (Aug 10)
- Re: [anti-XSS]about CERT/CC:malicious_code_mitigation Valdis . Kletnieks (Aug 10)
- Re: [anti-XSS]about CERT/CC:malicious_code_mitigation dd (Aug 09)
- Re: [anti-XSS]about CERT/CC:malicious_code_mitigation Valdis . Kletnieks (Aug 09)
- <Possible follow-ups>
- Re: [anti-XSS]about CERT/CC:malicious_code_mitigation auto269562 (Aug 10)