Document DBD taint checking and its necessity.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@650339 13f79535-47bb-0310-9956-ffa450edef68

1 files changed, 32 insertions, 0 deletions

diff --git a/docs/manual/mod/mod_dbd.xml b/docs/manual/mod/mod_dbd.xml
index 266b0fcbb7..ae20019abc 100644
--- a/docs/manual/mod/mod_dbd.xml
+++ b/docs/manual/mod/mod_dbd.xml
@@ -114,6 +114,38 @@ APR_DECLARE_OPTIONAL_FN(void, ap_dbd_prepare, (server_rec*, const char*, const c
     or to provide their own directives and use <code>ap_dbd_prepare</code>.</p>
 </section>
 
+<section id="security">
+<title>SECURITY WARNING</title>
+    <p>Any web/database application needs to secure itself against SQL
+    injection attacks.  In most cases, Apache DBD is safe, because
+    applications use prepared statements, and untrusted inputs are
+    only ever used as data.  Of course, if you use it via third-party
+    modules, you should ascertain what precautions they may require.</p>
+    <p>However, the <var>FreeTDS</var> driver is inherently
+    <strong>unsafe</strong>.  The underlying library doesn't support
+    prepared statements, so the driver emulates them, and the
+    untrusted input is merged into the SQL statement.</p>
+    <p>It can be made safe by <em>untainting</em> all inputs:
+    a process inspired by Perl's taint checking.  Each input
+    is matched against a regexp, and only the match is used.
+    To use this, the untainting regexps must be included in the
+    prepared statements configured.  The regexp follows immediately
+    after the % in the prepared statement, and is enclosed in
+    curly brackets {}.  For example, if your application expects
+    alphanumeric input, you can use:</p>
+    <example>
+       <code>"SELECT foo FROM bar WHERE input = %s"</code>
+    </example>
+    <p>with other drivers, and suffer nothing worse than a failed query.
+    But with FreeTDS you'd need:</p>
+    <example>
+       <code>"SELECT foo FROM bar WHERE input = %{([A-Za-z0-9]+)}s"</code>
+    </example>
+    <p>Now anything that doesn't match the regexp's $1 match is
+    discarded, so the statement is safe.</p>
+    <p>An alternative to this may be the third-party ODBC driver,
+    which offers the security of genuine prepared statements.</p>
+</section>
 <directivesynopsis>
 <name>DBDriver</name>
 <description>Specify an SQL driver</description>