Re: Re: Re: Re: Re: Re: Re: Re: How Internet is a mess. (Playing with HTTPD)

This one is indead IlyaM proof :) I stared on it for 5 mins and I could not find how it can be abused ++. Anyway I'm not sure I like this approach because it is very easy to do mistakes. I would not use regexps on whole string but I'd split path on components first and then I'd use regexps on them. I.e. something like:

use URI;
my $uri = URI->new($path);
die "bad schema" unless is_safe_schema($uri->schema);
die "bad domain" unless is_safe_domain($uri->host);
die "bad path" unless is_safe_path($uri->path);

sub is_safe_schema {
    # left as excersize to reader
}

sub is_safe_domain {
    # left as excersize to reader
}

sub is_safe_path {
    my $path = shift;
    my @comps = split '/', $path;
    for my $comp (@comps) {
        return 0 unless is_safe_path_comp
    }
    return 1;
}

sub is_safe_path_comp {
    my $comp = shift;
    return 0 if $comp =~ /\0\\/;
    return 0 if $comp eq '..';
    # other unsafe patterns
    ....
    return 1;
}
[download]

--
Ilya Martynov, ilya@iponweb.net
CTO IPonWEB (UK) Ltd
Quality Perl Programming and Unix Support UK managed @ offshore prices - http://www.iponweb.net
Personal website - http://martynov.org

Comment on Re: Re: Re: Re: Re: Re: Re: Re: How Internet is a mess. (Playing with HTTPD) Download Code

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Re: How Internet is a mess. (Playing with HTTPD) by Abigail-II (Bishop) on Feb 28, 2003 at 12:52 UTC
That would consider `http://www.example.com/path/some/where?query/../here` [download] to be unsafe. You might first want to split on a question mark, and then inspect just the first part. Abigail	[reply] [d/l]
Re: Re: How Internet is a mess. (Playing with HTTPD) by IlyaM (Parson) on Feb 28, 2003 at 12:57 UTC
It is handled by URI module: `use URI; my $uri = URI->new('http://www.example.com/path/some/where?query/../he +re'); print "Path: ", $uri->path, "\n"; print "Query: ", $uri->query, "\n"; __END__ Prints: Path: /path/some/where Query: query/../here` [download] -- Ilya Martynov, ilya@iponweb.net CTO IPonWEB (UK) Ltd Quality Perl Programming and Unix Support UK managed @ offshore prices - http://www.iponweb.net Personal website - http://martynov.org	[reply] [d/l]
Re: Re: Re: Re: Re: Re: Re: Re: Re: How Internet is a mess. (Playing with HTTPD) by tachyon (Chancellor) on Feb 28, 2003 at 12:48 UTC
While I can see the merit in this approach there is a lot of redundancy with the potential for holes . It does of course offer more granularity but I'm not sure you really need this and the attendant overhead. The main issues are the null byte hack, shell metachars, multiencoding %hh so you don't actually properly check the string and the old ../.. chestnut. We are reasonably protected from buffer overflows but you can easily truncate the length if desired. cheers tachyon s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print	[reply]