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better description of the SQL injection examples
git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@68311 c90b9560-bf6c-de11-be94-00142212c4b1
This commit is contained in:
Gyozo Papp
parent
b003872755
commit
d9d0ce4b19
2 changed files with 110 additions and 94 deletions
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@ -1,5 +1,5 @@
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<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.41 $ -->
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<!-- $Revision: 1.42 $ -->
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<chapter id="security">
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<title>Security</title>
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@ -498,8 +498,8 @@ if (!ereg('^[^./][^/]*$', $username))
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<simpara>
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To retrieve or to store any information you need to connect to the database,
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send a legitimate query, fetch the result, and close the connecion.
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Nowadays, the commonly used interface in the interaction with databases is
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the Structured Query Language (SQL). See how an attacker can <link
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Nowadays, the commonly used query language in this interaction is the
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Structured Query Language (SQL). See how an attacker can <link
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linkend="security.database.sql-injection">tamper with an SQL query</link>.
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</simpara>
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<simpara>
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@ -636,16 +636,13 @@ else {
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Direct SQL Command Injection is a technique where an attacker creates or
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alters existing SQL commands to expose hidden data, or to override valuable
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ones, or even to execute dangerous system level commands on the database
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host.
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</simpara>
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<simpara>
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This is accomplished by the application taking user input and combining
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it with static parameters to build a SQL query. The following examples
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are based on true stories, unfortunately.
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host. This is accomplished by the application taking user input and
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combining it with static parameters to build a SQL query. The following
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examples are based on true stories, unfortunately.
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</simpara>
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<para>
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Owing to the lack of input validation and connecting to the database on
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behalf of a superuser or the owner who can create users, the attacker
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behalf of a superuser or the one who can create users, the attacker
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may create a superuser in your database.
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<example>
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<title>
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@ -657,6 +654,8 @@ else {
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$offset = argv[0]; // beware, no input validation!
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$query = "SELECT id, name FROM products ORDER BY name LIMIT 20 OFFSET $offset;";
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$result = pg_exec($conn, $query);
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// with MySQL:
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$result = mysql_query($query);
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]]>
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</programlisting>
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</example>
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@ -669,17 +668,6 @@ $result = pg_exec($conn, $query);
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<programlisting>
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<![CDATA[
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0;
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insert into pg_shadow(usename,usesysid,usesuper,usecatupd,passwd)
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values ('crack', 31, 't','t','crack');
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--
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]]>
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</programlisting>
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</informalexample>
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or more precisely:
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<informalexample>
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<programlisting>
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<![CDATA[
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0;
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insert into pg_shadow(usename,usesysid,usesuper,usecatupd,passwd)
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select 'crack', usesysid, 't','t','crack'
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from pg_shadow where usename='postgres';
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@ -709,14 +697,23 @@ FLUSH PRIVILEGES;
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</para>
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</note>
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<para>
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A feasible way to gain passwords:
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A feasible way to gain passwords is to circumvent your search result pages.
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What the attacker has to do is only trying if there is a submitted filter
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setting handled not properly. These filters are commonly set in a previous
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form to customize <literal>WHERE, ORDER BY, LIMIT and OFFSET</literal>
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clauses in <literal>SELECT</literal> statements. If your database supports
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the <literal>UNION</literal> construct, the attacker may try to append an
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entire query to the original one to list passwords from an arbitrary table.
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Using encrypted password fields is strongly encouraged.
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<example>
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<title>
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Listing out articles ... and some passwords (any database server)
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</title>
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<programlisting role="php">
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<![CDATA[
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$query = "SELECT id, name, inserted, size FROM products WHERE size = '$size';";
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$query = "SELECT id, name, inserted, size FROM products
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WHERE size = '$size'
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ORDER BY $order LIMIT $limit, $offset;";
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]]>
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</programlisting>
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</example>
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@ -725,15 +722,24 @@ $query = "SELECT id, name, inserted, size FROM products WHERE size = '$size';";
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<informalexample>
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<programlisting>
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<![CDATA[
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union select '1', concat(uname||'-'||passwd) as name, '1971-01-01', '0' from usertable
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'
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union select '1', concat(uname||'-'||passwd) as name, '1971-01-01', '0' from usertable;
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--
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]]>
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</programlisting>
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</informalexample>
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If this query were assigned to <varname>$size</varname> (prepended with
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<literal>'</literal>), the query beast awakened.
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If this query (playing with the <literal>'</literal> and
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<literal>--</literal>) were assigned to one of the variables used in
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<varname>$query</varname>, the query beast awakened.
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</para>
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<para>
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SQL UPDATEs are also subject to attacking your database.
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SQL UPDATEs are also subject to attacking your database. These queries are
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also threatened by chopping and appending an entirely new query to it. But
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the attacker might fiddle with the <literal>SET</literal> clause. In this
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case some schema information must be possessed to manipulate the query
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successfully. This can be acquired by examing the form variable names, or
|
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just simply brute forcing. There are not so many naming convention for
|
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fields storing passwords or usernames.
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<example>
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<title>
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From resetting a password ... to gaining more privileges (any database server)
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|
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@ -745,22 +751,16 @@ $query = "UPDATE usertable SET pwd='$pwd' WHERE uid='$uid';";
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</programlisting>
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</example>
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But a malicious user sumbits the value
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<literal>' or uid like'%admin%'; --</literal> to <varname>$uid</varname>,
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and the query will be twisted:
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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$query = "UPDATE usertable SET pwd='...' WHERE uid='' or like '%admin%'; --";
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]]>
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</programlisting>
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</informalexample>
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Now, the admin user password has been changed. Alternatively, the attacker
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simply sets <varname>$pwd</varname> to
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<literal>"hehehe', admin='yes', trusted=100 </literal> (with a trailing
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space) to gain more privileges:
|
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<literal>' or uid like'%admin%'; --</literal> to <varname>$uid</varname> to
|
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change the admin's password, or simply sets <varname>$pwd</varname> to
|
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<literal>"hehehe', admin='yes', trusted=100 "</literal> (with a trailing
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space) to gain more privileges. Then, the query will be twisted:
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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// $uid == ' or uid like'%admin%'; --
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$query = "UPDATE usertable SET pwd='...' WHERE uid='' or uid like '%admin%'; --";
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// $pwd == "hehehe', admin='yes', trusted=100 "
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$query = "UPDATE usertable SET pwd='hehehe', admin='yes', trusted=100 WHERE ...;"
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]]>
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</programlisting>
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@ -818,19 +818,26 @@ $result = mssql_query($query);
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<simpara>
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These attacks are mainly based on exploiting the code not being written
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with security in mind. Never trust on any kind of input, especially
|
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which comes from the client side. The first example shows that such a
|
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which comes from the client side, even though it comes from a select box,
|
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a hidden input field or a cookie. The first example shows that such a
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blameless query can cause disasters.
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</simpara>
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<itemizedlist>
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<listitem>
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<simpara>
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First, check if the given input has the expected data type. PHP has
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Never connect to the database as a superuser or as the database owner.
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Use always customized users with very limited privileges.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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Check if the given input has the expected data type. PHP has
|
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a wide range of input validating functions, from the simplest ones
|
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found in <link linkend="ref.variables">Variable Functions</link> and
|
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in <link linkend="ref.ctype">Character Type Functions</link>
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sections, (e.g. <function>is_numeric</function>,
|
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<function>ctype_digit</function> respectively) onwards the
|
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(e.g. <function>is_numeric</function>, <function>ctype_digit</function>
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respectively) onwards the
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<link linkend="ref.pcre">Perl compatible Regular Expressions</link>
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support.
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</simpara>
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@ -839,7 +846,8 @@ $result = mssql_query($query);
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<para>
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If the application waits for numeric input, consider to verify data
|
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with <function>is_numeric</function>, or silently change its type
|
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using <function>settype</function> or <function>sprintf()</function>.
|
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using <function>settype</function>, or use its numeric representation
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by <function>sprintf</function>.
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<example>
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<title>A more secure way to compose a query for paging</title>
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<programlisting role="php">
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@ -856,9 +864,9 @@ $query = sprintf("SELECT id, name FROM products ORDER BY name LIMIT 20 OFFSET %
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</listitem>
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<listitem>
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<simpara>
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Quote user input which is passed to the database with
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Quote each non numeric user input which is passed to the database with
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<function>addslashes</function> or <function>addcslashes</function>.
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See <link linkend="security.database.storage">this example</link>.
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See <link linkend="security.database.storage">the first example</link>.
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As the examples shows, quotes burnt into the static part of the query
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is not enough, and can be easily hacked.
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</simpara>
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@ -1,5 +1,5 @@
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<?xml version="1.0" encoding="iso-8859-1"?>
|
||||
<!-- $Revision: 1.41 $ -->
|
||||
<!-- $Revision: 1.42 $ -->
|
||||
<chapter id="security">
|
||||
<title>Security</title>
|
||||
|
||||
|
|
@ -498,8 +498,8 @@ if (!ereg('^[^./][^/]*$', $username))
|
|||
<simpara>
|
||||
To retrieve or to store any information you need to connect to the database,
|
||||
send a legitimate query, fetch the result, and close the connecion.
|
||||
Nowadays, the commonly used interface in the interaction with databases is
|
||||
the Structured Query Language (SQL). See how an attacker can <link
|
||||
Nowadays, the commonly used query language in this interaction is the
|
||||
Structured Query Language (SQL). See how an attacker can <link
|
||||
linkend="security.database.sql-injection">tamper with an SQL query</link>.
|
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</simpara>
|
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<simpara>
|
||||
|
|
@ -636,16 +636,13 @@ else {
|
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Direct SQL Command Injection is a technique where an attacker creates or
|
||||
alters existing SQL commands to expose hidden data, or to override valuable
|
||||
ones, or even to execute dangerous system level commands on the database
|
||||
host.
|
||||
</simpara>
|
||||
<simpara>
|
||||
This is accomplished by the application taking user input and combining
|
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it with static parameters to build a SQL query. The following examples
|
||||
are based on true stories, unfortunately.
|
||||
host. This is accomplished by the application taking user input and
|
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combining it with static parameters to build a SQL query. The following
|
||||
examples are based on true stories, unfortunately.
|
||||
</simpara>
|
||||
<para>
|
||||
Owing to the lack of input validation and connecting to the database on
|
||||
behalf of a superuser or the owner who can create users, the attacker
|
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behalf of a superuser or the one who can create users, the attacker
|
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may create a superuser in your database.
|
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<example>
|
||||
<title>
|
||||
|
|
@ -657,6 +654,8 @@ else {
|
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$offset = argv[0]; // beware, no input validation!
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$query = "SELECT id, name FROM products ORDER BY name LIMIT 20 OFFSET $offset;";
|
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$result = pg_exec($conn, $query);
|
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// with MySQL:
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$result = mysql_query($query);
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]]>
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</programlisting>
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</example>
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|
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@ -669,17 +668,6 @@ $result = pg_exec($conn, $query);
|
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<programlisting>
|
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<![CDATA[
|
||||
0;
|
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insert into pg_shadow(usename,usesysid,usesuper,usecatupd,passwd)
|
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values ('crack', 31, 't','t','crack');
|
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--
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]]>
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</programlisting>
|
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</informalexample>
|
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or more precisely:
|
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<informalexample>
|
||||
<programlisting>
|
||||
<![CDATA[
|
||||
0;
|
||||
insert into pg_shadow(usename,usesysid,usesuper,usecatupd,passwd)
|
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select 'crack', usesysid, 't','t','crack'
|
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from pg_shadow where usename='postgres';
|
||||
|
|
@ -709,14 +697,23 @@ FLUSH PRIVILEGES;
|
|||
</para>
|
||||
</note>
|
||||
<para>
|
||||
A feasible way to gain passwords:
|
||||
A feasible way to gain passwords is to circumvent your search result pages.
|
||||
What the attacker has to do is only trying if there is a submitted filter
|
||||
setting handled not properly. These filters are commonly set in a previous
|
||||
form to customize <literal>WHERE, ORDER BY, LIMIT and OFFSET</literal>
|
||||
clauses in <literal>SELECT</literal> statements. If your database supports
|
||||
the <literal>UNION</literal> construct, the attacker may try to append an
|
||||
entire query to the original one to list passwords from an arbitrary table.
|
||||
Using encrypted password fields is strongly encouraged.
|
||||
<example>
|
||||
<title>
|
||||
Listing out articles ... and some passwords (any database server)
|
||||
</title>
|
||||
<programlisting role="php">
|
||||
<![CDATA[
|
||||
$query = "SELECT id, name, inserted, size FROM products WHERE size = '$size';";
|
||||
$query = "SELECT id, name, inserted, size FROM products
|
||||
WHERE size = '$size'
|
||||
ORDER BY $order LIMIT $limit, $offset;";
|
||||
]]>
|
||||
</programlisting>
|
||||
</example>
|
||||
|
|
@ -725,15 +722,24 @@ $query = "SELECT id, name, inserted, size FROM products WHERE size = '$size';";
|
|||
<informalexample>
|
||||
<programlisting>
|
||||
<![CDATA[
|
||||
union select '1', concat(uname||'-'||passwd) as name, '1971-01-01', '0' from usertable
|
||||
'
|
||||
union select '1', concat(uname||'-'||passwd) as name, '1971-01-01', '0' from usertable;
|
||||
--
|
||||
]]>
|
||||
</programlisting>
|
||||
</informalexample>
|
||||
If this query were assigned to <varname>$size</varname> (prepended with
|
||||
<literal>'</literal>), the query beast awakened.
|
||||
If this query (playing with the <literal>'</literal> and
|
||||
<literal>--</literal>) were assigned to one of the variables used in
|
||||
<varname>$query</varname>, the query beast awakened.
|
||||
</para>
|
||||
<para>
|
||||
SQL UPDATEs are also subject to attacking your database.
|
||||
SQL UPDATEs are also subject to attacking your database. These queries are
|
||||
also threatened by chopping and appending an entirely new query to it. But
|
||||
the attacker might fiddle with the <literal>SET</literal> clause. In this
|
||||
case some schema information must be possessed to manipulate the query
|
||||
successfully. This can be acquired by examing the form variable names, or
|
||||
just simply brute forcing. There are not so many naming convention for
|
||||
fields storing passwords or usernames.
|
||||
<example>
|
||||
<title>
|
||||
From resetting a password ... to gaining more privileges (any database server)
|
||||
|
|
@ -745,22 +751,16 @@ $query = "UPDATE usertable SET pwd='$pwd' WHERE uid='$uid';";
|
|||
</programlisting>
|
||||
</example>
|
||||
But a malicious user sumbits the value
|
||||
<literal>' or uid like'%admin%'; --</literal> to <varname>$uid</varname>,
|
||||
and the query will be twisted:
|
||||
<informalexample>
|
||||
<programlisting role="php">
|
||||
<![CDATA[
|
||||
$query = "UPDATE usertable SET pwd='...' WHERE uid='' or like '%admin%'; --";
|
||||
]]>
|
||||
</programlisting>
|
||||
</informalexample>
|
||||
Now, the admin user password has been changed. Alternatively, the attacker
|
||||
simply sets <varname>$pwd</varname> to
|
||||
<literal>"hehehe', admin='yes', trusted=100 </literal> (with a trailing
|
||||
space) to gain more privileges:
|
||||
<literal>' or uid like'%admin%'; --</literal> to <varname>$uid</varname> to
|
||||
change the admin's password, or simply sets <varname>$pwd</varname> to
|
||||
<literal>"hehehe', admin='yes', trusted=100 "</literal> (with a trailing
|
||||
space) to gain more privileges. Then, the query will be twisted:
|
||||
<informalexample>
|
||||
<programlisting role="php">
|
||||
<![CDATA[
|
||||
// $uid == ' or uid like'%admin%'; --
|
||||
$query = "UPDATE usertable SET pwd='...' WHERE uid='' or uid like '%admin%'; --";
|
||||
// $pwd == "hehehe', admin='yes', trusted=100 "
|
||||
$query = "UPDATE usertable SET pwd='hehehe', admin='yes', trusted=100 WHERE ...;"
|
||||
]]>
|
||||
</programlisting>
|
||||
|
|
@ -818,19 +818,26 @@ $result = mssql_query($query);
|
|||
<simpara>
|
||||
These attacks are mainly based on exploiting the code not being written
|
||||
with security in mind. Never trust on any kind of input, especially
|
||||
which comes from the client side. The first example shows that such a
|
||||
which comes from the client side, even though it comes from a select box,
|
||||
a hidden input field or a cookie. The first example shows that such a
|
||||
blameless query can cause disasters.
|
||||
</simpara>
|
||||
|
||||
<itemizedlist>
|
||||
<listitem>
|
||||
<simpara>
|
||||
First, check if the given input has the expected data type. PHP has
|
||||
Never connect to the database as a superuser or as the database owner.
|
||||
Use always customized users with very limited privileges.
|
||||
</simpara>
|
||||
</listitem>
|
||||
<listitem>
|
||||
<simpara>
|
||||
Check if the given input has the expected data type. PHP has
|
||||
a wide range of input validating functions, from the simplest ones
|
||||
found in <link linkend="ref.variables">Variable Functions</link> and
|
||||
in <link linkend="ref.ctype">Character Type Functions</link>
|
||||
sections, (e.g. <function>is_numeric</function>,
|
||||
<function>ctype_digit</function> respectively) onwards the
|
||||
(e.g. <function>is_numeric</function>, <function>ctype_digit</function>
|
||||
respectively) onwards the
|
||||
<link linkend="ref.pcre">Perl compatible Regular Expressions</link>
|
||||
support.
|
||||
</simpara>
|
||||
|
|
@ -839,7 +846,8 @@ $result = mssql_query($query);
|
|||
<para>
|
||||
If the application waits for numeric input, consider to verify data
|
||||
with <function>is_numeric</function>, or silently change its type
|
||||
using <function>settype</function> or <function>sprintf()</function>.
|
||||
using <function>settype</function>, or use its numeric representation
|
||||
by <function>sprintf</function>.
|
||||
<example>
|
||||
<title>A more secure way to compose a query for paging</title>
|
||||
<programlisting role="php">
|
||||
|
|
@ -856,9 +864,9 @@ $query = sprintf("SELECT id, name FROM products ORDER BY name LIMIT 20 OFFSET %
|
|||
</listitem>
|
||||
<listitem>
|
||||
<simpara>
|
||||
Quote user input which is passed to the database with
|
||||
Quote each non numeric user input which is passed to the database with
|
||||
<function>addslashes</function> or <function>addcslashes</function>.
|
||||
See <link linkend="security.database.storage">this example</link>.
|
||||
See <link linkend="security.database.storage">the first example</link>.
|
||||
As the examples shows, quotes burnt into the static part of the query
|
||||
is not enough, and can be easily hacked.
|
||||
</simpara>
|
||||
|
|
|
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Loading…
Reference in a new issue