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Re: PHP processing steps to apply to a URL to make it safe

From Arno Welzel <usenet@arnowelzel.de>
Newsgroups comp.lang.php
Subject Re: PHP processing steps to apply to a URL to make it safe
Date 2016-02-18 08:02 +0100
Message-ID <56C56CA2.6060601@arnowelzel.de> (permalink)
References <na1es3$rsd$1@dont-email.me> <56C445F6.1090008@arnowelzel.de> <na220i$27e$1@dont-email.me>

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James Harris schrieb am 2016-02-17 um 16:04:

> On 17/02/2016 10:05, Arno Welzel wrote:
>> James Harris schrieb am 2016-02-17 um 10:37:
>>
>>> In line with the principle of a program vetting its input, this is about
>>> vetting the supplied URL.
>>>
>>> In order to process a URL or parts of a URL in PHP what processing ought
>>> to be applied to it? I have been using some steps which I will write
>>> below but I am becoming increasingly uncertain that I have covered all
>>> the bases.
>>
>> Well - it depends for which reasons you want to process the URL.
> 
> It will go through a series of steps to change it and it will end up 
> identifying something in the file system or something in a database.

Ok - but in either case you end up in looking up for some information
based on what you get from the URL.

This means: Not the URL is unsafe, but the code which does the
information lookup may be unsafe.

[...]
>> There is no "normal" URL - in fact the "/" at the end is part of the URL.
> 
> The docs for request_uri (which I'll use as shorthand for the full 
> expression) did not specify whether leading or trailing slashes would be 
> present/maintained.

Yes - because it does not matter wethere there is a trailing slash or
not. Some URLs have a trailing slash, others don't. But both forms are
totally valid and there is no "normal" form with or without trailing slash.

>>>     check each character is from an allowed set
>>
>> Why?
> 
> My own insecurity, perhaps!

What do you suspect to happen if an "invalid" character is passed?
Again: Not URL itself is "unsafe" - just code which uses the information
may be unsafe.

>>>     check there are no // parts
>>
>> Why?
> 
> Because such would designate an empty path component as between "the" 
> and "bad" in http://site.com/this/is/the//bad/part.

So what? This is no problem at all, except when you write code which
relies on the fact, that there will ever by something between slashes.

In fact, using "//" doesn't even change the result in many cases:

<http://arnowelzel.de/wp/en/a-week-with-the-pebble>
<http://arnowelzel.de/wp/en//a-week-with-the-pebble>
<http://arnowelzel.de//wp//en//a-week-with-the-pebble>

>>>     check there are no .. parts
>>
>> Why?
> 
> Because that indicates the parent directory and can be used to move 'up' 
> a level in the path hierarchy. It is thus insecure.

It is only insecure, if the webserver does not sanitize the path. Apache
and nginx won't let you get outside the root directory this way.

However - if YOUR code will use that information to access a file using
the given "path" of the URL this may be a problem. But in this case you
should better use realpath() to check if the path is still within its
allowed limits.

[...]
>> As I said: It depends on what you want to achieve - do you make sure the
>> URL you get is valid? Do you want to parse the URL in any way?
> 
> The URL component (request_uri) will be mapped to a file or a database 
> entry in this case.

So why don't you just use the whole URI and use it in a prepared SELECT
statement? In that case it's just not important, what the URI contains.
Either there is an entry for that URI in the database or not. But it
doesn't matter what the URI itself contains if it's just treated as text
and used as parameter in a prepared statement.

Of course you should NOT use the URI and just add it as text in the
SELECT statement - use a pepared statement.


-- 
Arno Welzel
http://arnowelzel.de
http://de-rec-fahrrad.de
http://fahrradzukunft.de

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Thread

PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-17 09:37 +0000
  Re: PHP processing steps to apply to a URL to make it safe Arno Welzel <usenet@arnowelzel.de> - 2016-02-17 11:05 +0100
    Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-17 15:04 +0000
      Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-17 10:54 -0500
        Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-18 01:09 +0000
          Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-17 21:12 -0500
            Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-20 19:07 +0000
              Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-20 21:07 +0100
                Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-20 20:35 +0000
                Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-20 21:40 +0100
                Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-20 21:02 +0000
              Re: PHP processing steps to apply to a URL to make it safe gordonb.lkcah@burditt.org (Gordon Burditt) - 2016-02-29 21:29 -0600
      Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-17 23:33 +0100
        Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-18 01:12 +0000
          Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-18 21:48 +0100
        Re: PHP processing steps to apply to a URL to make it safe Arno Welzel <usenet@arnowelzel.de> - 2016-02-18 08:05 +0100
          Re: PHP processing steps to apply to a URL to make it safe Tim Streater <timstreater@greenbee.net> - 2016-02-18 09:59 +0000
            Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-18 10:29 +0000
              Re: PHP processing steps to apply to a URL to make it safe Tim Streater <timstreater@greenbee.net> - 2016-02-18 11:36 +0000
            Re: PHP processing steps to apply to a URL to make it safe Arno Welzel <usenet@arnowelzel.de> - 2016-02-18 15:44 +0100
          Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-18 21:47 +0100
      Re: PHP processing steps to apply to a URL to make it safe Arno Welzel <usenet@arnowelzel.de> - 2016-02-18 08:02 +0100
        Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-20 19:29 +0000
          Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-20 21:37 +0100
            Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-20 21:37 +0000
              Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-21 15:02 +0100
                Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-21 15:02 +0000
  Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-17 08:19 -0500
    Re: PHP processing steps to apply to a URL to make it safe "R.Wieser" <address@not.available> - 2016-02-17 14:43 +0100
      Re: PHP processing steps to apply to a URL to make it safe Arno Welzel <usenet@arnowelzel.de> - 2016-02-17 15:04 +0100
        Re: PHP processing steps to apply to a URL to make it safe "R.Wieser" <address@not.available> - 2016-02-17 15:17 +0100
          Re: PHP processing steps to apply to a URL to make it safe Arno Welzel <usenet@arnowelzel.de> - 2016-02-17 15:47 +0100
            Re: PHP processing steps to apply to a URL to make it safe "R.Wieser" <address@not.available> - 2016-02-17 15:57 +0100
              Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-17 10:57 -0500
                Re: PHP processing steps to apply to a URL to make it safe "R.Wieser" <address@not.available> - 2016-02-17 17:10 +0100
                Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-17 12:11 -0500
                Re: PHP processing steps to apply to a URL to make it safe "R.Wieser" <address@not.available> - 2016-02-17 18:51 +0100
                Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-17 12:55 -0500
              Re: PHP processing steps to apply to a URL to make it safe Arno Welzel <usenet@arnowelzel.de> - 2016-02-17 19:06 +0100
                Re: PHP processing steps to apply to a URL to make it safe "R.Wieser" <address@not.available> - 2016-02-17 20:19 +0100
                Re: PHP processing steps to apply to a URL to make it safe Arno Welzel <usenet@arnowelzel.de> - 2016-02-18 08:18 +0100
                Re: PHP processing steps to apply to a URL to make it safe "R.Wieser" <address@not.available> - 2016-02-18 09:20 +0100
                Re: PHP processing steps to apply to a URL to make it safe Arno Welzel <usenet@arnowelzel.de> - 2016-02-18 15:48 +0100
                Re: PHP processing steps to apply to a URL to make it safe "R.Wieser" <address@not.available> - 2016-02-18 16:25 +0100
                Re: PHP processing steps to apply to a URL to make it safe Arno Welzel <usenet@arnowelzel.de> - 2016-02-18 17:00 +0100
                Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-18 22:26 +0100
                Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-18 10:48 -0500
            Re: PHP processing steps to apply to a URL to make it safe "Christoph M. Becker" <cmbecker69@arcor.de> - 2016-02-17 16:38 +0100
              Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-17 10:56 -0500
              Re: PHP processing steps to apply to a URL to make it safe Arno Welzel <usenet@arnowelzel.de> - 2016-02-17 19:08 +0100
              Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-17 23:35 +0100
          Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-17 09:56 -0500
            Re: PHP processing steps to apply to a URL to make it safe "R.Wieser" <address@not.available> - 2016-02-17 16:44 +0100
              Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-17 12:12 -0500
                Re: PHP processing steps to apply to a URL to make it safe "R.Wieser" <address@not.available> - 2016-02-17 19:04 +0100
      Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-17 09:55 -0500
        Re: PHP processing steps to apply to a URL to make it safe "R.Wieser" <address@not.available> - 2016-02-17 16:39 +0100
          Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-17 11:00 -0500
    Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-17 15:15 +0000
      Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-17 11:05 -0500
        Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-18 01:18 +0000
      Re: PHP processing steps to apply to a URL to make it safe Arno Welzel <usenet@arnowelzel.de> - 2016-02-17 19:14 +0100
        Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-18 00:19 +0000
      Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-17 23:36 +0100
  Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-17 23:26 +0100
    Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-18 00:36 +0000
      Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-18 22:03 +0100
        Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-20 19:38 +0000
          Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-20 21:17 +0100
            Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-20 20:56 +0000
              Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-20 23:48 +0100
                Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-21 09:37 +0000
                Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-21 14:42 +0100
                Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-21 15:03 +0000
                Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-21 14:09 -0500
                Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-21 19:34 +0000
                Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-21 14:49 -0500
                Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-21 19:56 +0000
                Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-21 20:29 -0500
                Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-22 07:30 +0000
                Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-22 08:13 -0500
                Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-22 15:01 +0000
                Re: PHP processing steps to apply to a URL to make it safe Jerry Stuckle <jstucklex@attglobal.net> - 2016-02-22 10:31 -0500
                Re: PHP processing steps to apply to a URL to make it safe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-22 00:10 +0100
                Re: PHP processing steps to apply to a URL to make it safe James Harris <james.harris.1@gmail.com> - 2016-02-21 23:45 +0000
  Re: PHP processing steps to apply to a URL to make it safe pittendrigh <Sandy.Pittendrigh@gmail.com> - 2016-03-22 05:23 -0700

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