Thread: Protection from SQL injection

Hi,

As you know, "SQL injection" is the main security problem of databases today.

I think I have a solution: 'disabling literals'. Or you may call it
'enforcing the use of parameterized statements'. This means that SQL
statements with embedded user input are rejected at runtime. My
solution goes beyond saying "developers ~should~ use parameterized
statements". That is not a solution because developers are lazy. My
solution is: "developers MUST use parameterized statements". It goes
like this: Literals are disabled using the SQL statement:

SET ALLOW_LITERALS NONE;

Afterwards, SQL statements with text are not allowed any more. That
means, SQL statement of the form "SELECT * FROM USERS WHERE
PASSWORD='qerkllkj'" will fail with the exception 'Literals are not
allowed, please use parameters'. It is like the database does not know
what ='qerkllkj' means. Only statements of the secure form are
allowed, for example "SELECT * FROM USERS WHERE PASSWORD=?". This
solves the problem because SQL injection is almost impossible if user
input is not directly embedded in SQL statements.

The 'ALLOW_LITERALS NONE' mode is enabled by the developer itself, or
by an administrator. It is still possible to generate SQL statements
dynamically, and use the same APIs as before, as long as SQL
statements don't include literals. Literals can still be used when
using query tools, or in applications considered 'safe'. To ease
converting the application to use parameterized queries, there should
be a second mode where number literals are allowed: SET ALLOW_LITERALS
NUMBERS. To allow all literals, execute SET ALLOW_LITERALS ALL (this
is the default setting).

So far this feature is implemented in my little database H2. More
information about this feature is described here:
http://www.h2database.com/html/advanced.html#sql_injection

What do you think about it? Do you think it makes sense to implement
this security feature in PostgreSQL as well? If not why not? Does
PostgreSQL have another solution or plan to solve the SQL injection
problem?

Regards,
Thomas

"Thomas Mueller" <thomas.tom.mueller@gmail.com> writes:
> SET ALLOW_LITERALS NONE;

I think you missed April Fool's Day...

This is just silly, as it makes life impossibly painful for users
(constants are hardly a useless part of SQL) and it doesn't really
plug any holes.  As an example:
select * from tab where intcol = intcol; delete from tab;

contains no literals and yet the delete is very probably injected.
        regards, tom lane

On Sat, Apr 26, 2008 at 11:32 AM, Thomas Mueller
<thomas.tom.mueller@gmail.com> wrote:
>
> The 'ALLOW_LITERALS NONE' mode is enabled by the developer itself, or
> by an administrator.


then it solves nothing...
what if the developer never SET ALLOW_LITERALS NONE or
maybe i can inject "select * from tab where intcol = intcol; set
allow_literals all; add any query you want"

-- 
regards,
Jaime Casanova
Soporte de PostgreSQL
Guayaquil - Ecuador
Cel. (593) 087171157

Hi,

>  I think you missed April Fool's Day...

This is absolutely not an April Fool idea :-) I must have made a bad
job explaining my idea.

>  This is just silly, as it makes life impossibly painful for users

You mean developers? No, developers should use parameterized queries anyway.

>  (constants are hardly a useless part of SQL)

Your are right. But it depends how you define 'constant'. In other
programming languages, constants are not always literals. Instead,
constants are defined like this:

#define ACTIVE 1  // C
final static int ACTIVE=1; // Java

As far as I know, this concept doesn't exist in the SQL. I suggest to
add this concept as well to the database engine:

CREATE CONSTANT [IF NOT EXISTS] newConstantName VALUE expression;
DROP CONSTANT [IF EXISTS] constantName;

Example:

CREATE CONSTANT PI VALUE 3.1415926535;
CREATE CONSTANT ACTIVE VALUE 1;
CREATE CONSTANT INACTIVE VALUE 0;

This also improves the program because you don't need to 'hard code'
numbers in the application:

SELECT * FROM USERS WHERE STATE=ACTIVE AND PASSWORD=?

> it doesn't really plug any holes.

Sure it does.

> As an example:
> select * from tab where intcol = intcol; delete from tab;

How would the application that executed this statement would look like? In Java:

ResultSet rs = stat.executeQuery("select * from tab where " + userInput);

Such a program wouldn't make any sense, right? Do you mean this?

ResultSet rs = stat.executeQuery("select * from tab where state = " +
userInput);

If literals are disabled, the database would reject any number. The
program wouldn't work in the normal case any longer if literals are
disabled. So the developer would have to change it to (otherwise his
application doesn't work) to:

PreparedStatement prep = conn.prepareStatement("select * from tab
where state = ?");
prep.setInt(1, userInput);...

This is save. There is no way to inject SQL here.

Regards,
Thomas

Hi,

>  > The 'ALLOW_LITERALS NONE' mode is enabled by the developer itself, or
>  > by an administrator.
>  then it solves nothing...
>  what if the developer never SET ALLOW_LITERALS NONE

As I have said, the 'ALLOW_LITERALS NONE' mode is enabled by the
developer itself, or by an administrator. The developer may be lazy,
but the administrator can enforce this policy.

>  maybe i can inject "select * from tab where intcol = intcol; set
>  allow_literals all; add any query you want"

How do you inject this? How would the application looks like where
this can be injected?

Regards,
Thomas

On Sat, Apr 26, 2008 at 1:19 PM, Thomas Mueller
<thomas.tom.mueller@gmail.com> wrote:
> Hi,
>
> >  > The 'ALLOW_LITERALS NONE' mode is enabled by the developer itself, or
> >  > by an administrator.
> >  then it solves nothing...
> >  what if the developer never SET ALLOW_LITERALS NONE
>
> As I have said, the 'ALLOW_LITERALS NONE' mode is enabled by the
> developer itself, or by an administrator. The developer may be lazy,
> but the administrator can enforce this policy.
>

but can't the developer allow literals again?

> >  maybe i can inject "select * from tab where intcol = intcol; set
> >  allow_literals all; add any query you want"
>
> How do you inject this? How would the application looks like where
> this can be injected?
>

ok... point taken

-- 
regards,
Jaime Casanova
Soporte de PostgreSQL
Guayaquil - Ecuador
Cel. (593) 087171157

Thomas Mueller wrote on 26.04.2008 18:32:
> Literals can still be used when using query tools, or in applications considered 'safe'. 
I fail to see how the backend could distinguish between a query sent by a query 
tool and a query sent by an "application".

Thomas

On Sat, Apr 26, 2008 at 3:32 PM, Thomas Kellerer <spam_eater@gmx.net> wrote:
> Thomas Mueller wrote on 26.04.2008 18:32:
>
> > Literals can still be used when using query tools, or in applications
> considered 'safe'.
> >
>  I fail to see how the backend could distinguish between a query sent by a
> query tool and a query sent by an "application".

Wouldn't it be much simpler to have a version of the libpq client lib
that only understands prepared queries?

"Scott Marlowe" <scott.marlowe@gmail.com> writes:
> Wouldn't it be much simpler to have a version of the libpq client lib
> that only understands prepared queries?

You could do that, but there's still no way for it to know exactly how
the submitted query was constructed.  This would block off the types of
injections that want to add whole SQL commands, but not ones that just
subvert the current query (eg adding OR TRUE to see data you shouldn't).

This is really a client problem and only client-side solutions will
provide meaningful traction for it.  In perl, for instance, the "taint"
mechanism is a good way to notice whether any insecure strings are
getting into database queries.
        regards, tom lane

On Sat, Apr 26, 2008 at 9:42 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> "Scott Marlowe" <scott.marlowe@gmail.com> writes:
>  > Wouldn't it be much simpler to have a version of the libpq client lib
>  > that only understands prepared queries?
>
>  You could do that, but there's still no way for it to know exactly how
>  the submitted query was constructed.  This would block off the types of
>  injections that want to add whole SQL commands, but not ones that just
>  subvert the current query (eg adding OR TRUE to see data you shouldn't).
>
>  This is really a client problem and only client-side solutions will
>  provide meaningful traction for it.  In perl, for instance, the "taint"
>  mechanism is a good way to notice whether any insecure strings are
>  getting into database queries.

Agreed.  My point was that to do what the OP wants, wouldn't it make
more sense to just lobotomize libpq so it doesn't understand anything
but prepared queries.  Doesn't obviate the need for a client side
language based solution.  Just seems to make WAY more sense than
trying to make the change at the server level in pgsql.

"Scott Marlowe" <scott.marlowe@gmail.com> writes:
> Agreed.  My point was that to do what the OP wants, wouldn't it make
> more sense to just lobotomize libpq so it doesn't understand anything
> but prepared queries.

I doubt that that particular lobotomization accomplishes much in
comparison to the penalties.

IIRC there was some discussion recently of providing a mode in which
the server would reject PQexec strings containing more than one query.
I didn't care for it much at the time, but I think it would provide
most of the benefit of these suggestions with far less compatibility
or performance hit.
        regards, tom lane

On Sat, Apr 26, 2008 at 9:58 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

>  IIRC there was some discussion recently of providing a mode in which
>  the server would reject PQexec strings containing more than one query.
>  I didn't care for it much at the time, but I think it would provide
>  most of the benefit of these suggestions with far less compatibility
>  or performance hit.

agreed.

And I trust (SQL) code review more than tying the hands of the programmers.

But I've always had the luxury of working with developers who liked me
as a DBA and were willing to do things my way, as far as the DB was
concerned anyway...

Hi,

>  but can't the developer allow literals again?

Executing the statement SET ALLOW_LITERALS should be restricted. The
application uses another user name / password and doesn't have to
access rights to enable it. Maybe the user name / password is
configured using JNDI, so the application developper has no influence
on that. In any case, even if the developer can enable literals, I
don't think he would, because he would be afraid to be caught
cheating.

Regards,
Thomas

Hi,

>  I fail to see how the backend could distinguish between a query sent by a
> query tool and a query sent by an "application".

The backend could use a different client library (a client library
that doesn't allow literals). But in this case two or three client
libraries are required.

Probably better is to restrict in the database.

There would be a user (or role) for the query tool and one for the
application. Maybe the SET ALLOW_LITERALS is not such a good idea.
What about REVOKE LITERAL_TEXT FROM APP_ROLE. So LITERAL_TEXT and
LITERAL_NUMBER would be rights (similar to REVOKE USAGE ON LANGUAGE
... FROM ...).

It's an access rights problem. Let's say there is a development
database (DEV_DB) and a production (PROD_DB). There are two users /
roles on those systems: APP_USER (no literals) and QUERY_TOOL_USER
(literals allowed). The passwords are different on each system.
Developers know the password for QUERY_TOOL_USER@DEV_DB and
APP_USER@DEV_DB, but only APP_USER@PROD_DB. Or developers know all
passwords, but the application configuration is rewieved not to use
QUERY_TOOL_USER.

Regards,
Thomas

Hi,

>  > Wouldn't it be much simpler to have a version of the libpq client lib
>  > that only understands prepared queries?

That would be possible. However the problem is not 'prepared queries'
versus 'direct queries'. It is possible to use literals in prepared
queries:

PreparedStatement prep = conn.prepareStatement( "SELECT * FROM USERS WHERE PASSWORD = '" + password + "');
prep.executeQuery();

This is unsafe. So you really need to filter on literals, and not on
the API. If you mean a library where literals not are allowed: that
would solve the problem, yes. However that would mean the client
library has to parse each SQL statement. That would complicate the
client library. Parsing is already done in the database engine,
technically it's better (long term) to disable literals there.

But it is possible to create a wrapper client library (for example a
JDBC wrapper driver) for other databases where literals are not
allowed. That would work for all databases.

>  You could do that, but there's still no way for it to know exactly how
>  the submitted query was constructed.  This would block off the types of
>  injections that want to add whole SQL commands, but not ones that just
>  subvert the current query (eg adding OR TRUE to see data you shouldn't).

In most cases you don't need to know how the query was constructed. If
the query uses parameters for all user input then it is (almost
always) safe. Only 'almost' because there is still a small gap: ORDER
BY injection. Example:

String order = input("order (id, name)?");
ResultSet rs = stat.executeQuery(   "SELECT ID, NAME FROM ITEMS ORDER BY " + order);

Sometimes the input comes from a web application (the user clicks on
the column header to sort on it).

See also http://code.google.com/p/h2database/source/browse/trunk/h2/src/test/org/h2/samples/SQLInjection.java

>  This is really a client problem and only client-side solutions will
>  provide meaningful traction for it.

This is like data validation on client side javascript. Yes, it's good
to have data validation there. But, the user could have Javascript
disabled. In any case it's better to have data validation on the
server side as well.

> In perl, for instance, the "taint" mechanism is a good way to notice whether any insecure strings are
>  getting into database queries.

There is no 'taint' mechanism in programming languages like Java.
Also, it requires that the application is reviewed. In the companies I
worked so far there were almost no code reviews. A lazy programmer can
still make mistakes.

Regards,
Thomas

Hi,

> providing a mode in which the server would reject PQexec strings containing more than one query.

That wouldn't help a lot. The simple SQL injection is not detected:

ResultSet rs = stat.executeQuery( "SELECT * FROM USERS WHERE PASSWORD='" + password + "'");

An attacker would only need to use the following password:

' OR 1=1

The the SQL statements is still only one query:

SELECT * FROM USERS WHERE PASSWORD='' OR 1=1

Regards,
Thomas

On Sat, 26 Apr 2008 23:24:59 -0600
"Scott Marlowe" <scott.marlowe@gmail.com> wrote:

> On Sat, Apr 26, 2008 at 9:58 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> 
> >  IIRC there was some discussion recently of providing a mode in
> > which the server would reject PQexec strings containing more than
> > one query. I didn't care for it much at the time, but I think it
> > would provide most of the benefit of these suggestions with far
> > less compatibility or performance hit.
> 
> agreed.

> And I trust (SQL) code review more than tying the hands of the
> programmers.

> But I've always had the luxury of working with developers who liked
> me as a DBA and were willing to do things my way, as far as the DB
> was concerned anyway...

what if you're the DBA and the dev and you don't trust yourself even
if you'd be willing to do the things your way ;)

-- 
Ivan Sergio Borgonovo
http://www.webthatworks.it

On Sat, 26 Apr 2008 21:50:10 -0600
"Scott Marlowe" <scott.marlowe@gmail.com> wrote:

> Agreed.  My point was that to do what the OP wants, wouldn't it make
> more sense to just lobotomize libpq so it doesn't understand
> anything but prepared queries.  Doesn't obviate the need for a
> client side language based solution.  Just seems to make WAY more
> sense than trying to make the change at the server level in pgsql.

The problem may be legacy code.

You'd like to statically point out places where multiple statements
could get injected.
All calls to your "query" function get routed to a wrapper that
actually call prepare/execute logic.
You do a BIG search&replace and see where your code fail cos you
actually needed more than one statement in a query.
Now you just have to grep your code for direct call to "plain"
queries during commit of your rcs.

My proposal was to add a switch that force routing to prepared
statement logic in libpq.

I'm thinking about situation in which you're using a library that
already wrap your query call.
You don't want to change the wrapper, so you don't want to take the
responsibility, sync troubles etc... of the library maintainer but
still you'd like to add a safety net to your code.

People dealing with your code would still see the familiar library
wrapper (you're not wrapping the wrapper) but you'd be able to switch
to "single statement mode".


Still ALLOW_LITERALS is a nice feature even if I think it won't fix
the notorious SQL injection problem forever.
Since it is going to make dev nervous because it adds code bloat
that's going to cause more bugs than the SQL injections it may
prevent.
Once you've developers that are so patient to write stuff like:

"select a.id, b.name from a join b on b.id=a.id where
a.status='pending' and b.id>7 and b.status='logged'"

into

"select a.id, b.name from a join b on b.id=a.id where
a.status=? and b.id>? and b.status=?", 'pending', 7, 'logged'

there are high chances they will prefer to spend some of their time
actually thinking about what they are writing.

I do know that thinking can't be taken for granted and that habits
and automatic methods may be generally preferable to "thinking", but
automatic methods works when they don't look painful.
Prepared statements force you to match input with position and it is
definitively error prone.

It is a tool... you may have some section of your code where that
parameter can't be changed, but most of the time you'll find it
useful if its default is set to NONE and dev *can* change it.

Now... let's think at the poor programmer...

He is writing a SQL statement that is static. He has to disable
ALLOW_LITERALS.
He is writing dynamic SQL that DON'T take user input.
ALLOW_LITERALS may still have some sense as a debugging tool but
there are high chances he will disable it to avoid other errors and
make coding simpler.
He is writing dynamic SQL that does take user input. He should be
forced to use ALLOW_LITTERALS NONE. But how can he be forced in the
middle of a program?
He is writing a "mixed" statement where some input is actually static
but not all... he may think it is easier to allow literals.

Everything is still in the hands of the dev.
Such setting may help you in static code evaluation since you may
spot easier the places where there could be breach of policy... but
still unless you want to make your dev life a hell... it is not going
to solve the SQL injection problem.

"mixed" statements that use external input and static input are quite
common and writing them avoiding literals may be a pain that your dev
won't be willing to suffer.

Queued statements in one query are far less common.

Still I do think that ALLOW_LITERAL is a valuable tool.
Same problems for legacy code apply.

-- 
Ivan Sergio Borgonovo
http://www.webthatworks.it

On Sun, 27 Apr 2008 12:38:48 +0200
Ivan Sergio Borgonovo <mail@webthatworks.it> wrote:

> Once you've developers that are so patient to write stuff like:
> 
> "select a.id, b.name from a join b on b.id=a.id where
> a.status='pending' and b.id>7 and b.status='logged'"
> 
> into
> 
> "select a.id, b.name from a join b on b.id=a.id where
> a.status=? and b.id>? and b.status=?", 'pending', 7, 'logged'
> 
> there are high chances they will prefer to spend some of their time
> actually thinking about what they are writing.

[snipped here and there]

> Prepared statements force you to match input with position and it is
> definitively error prone.

It'd be nice to have a wrapper that let you write prepared statements
this way:

"select a.id, b.name from a join b on a.id=b.id where
a.status=$variable1 and b.id>$variable2 etc... but that's a pretty
good change to any language parser.

Maybe it could be obtained by use of macro...
That will turn
new_query("select a.id, b.name from a join b on a.id=b.id where
a.status=$variable1 and b.id>$variable2");
into
pg_prepare('anonymous', 'select a.id, b.name from a join b on
a.id=b.id where a.status=$1 and b.id>$2');
pg_execute('anonymous',array($variable1,$variable2));

but aren't macro evil

Still it would be handy.

-- 
Ivan Sergio Borgonovo
http://www.webthatworks.it

Ivan Sergio Borgonovo wrote:
> It'd be nice to have a wrapper that let you write prepared statements
> this way:
>
> "select a.id, b.name from a join b on a.id=b.id where
> a.status=$variable1 and b.id>$variable2 etc... but that's a pretty
> good change to any language parser.
>   

Python already supports something like that. See PEP 249 
(http://www.python.org/dev/peps/pep-0249/), under Module Interface, the 
description of the paramstyle parameter. Psycopg2 supports both the 
"format" (C printf) and "pyformat" styles. See the last section on this 
page for an example using the pyformat style: 
http://www.devx.com/opensource/Article/29071/0/page/3.

Joe

On Sun, 27 Apr 2008 11:55:18 -0400
Joe <dev@freedomcircle.net> wrote:

> Ivan Sergio Borgonovo wrote:
> > It'd be nice to have a wrapper that let you write prepared
> > statements this way:
> >
> > "select a.id, b.name from a join b on a.id=b.id where
> > a.status=$variable1 and b.id>$variable2 etc... but that's a pretty
> > good change to any language parser.

> Python already supports something like that. See PEP 249 
> (http://www.python.org/dev/peps/pep-0249/), under Module Interface,
> the description of the paramstyle parameter. Psycopg2 supports both
> the "format" (C printf) and "pyformat" styles. See the last section
> on this page for an example using the pyformat style: 
> http://www.devx.com/opensource/Article/29071/0/page/3.

That's better than nothing but it is still a lot of code duplication.
You've to write column names in the sql statement and in the array
and... column values are not contextual to the statement.
That's easy... while what I wrote above does look as requiring a
really special parser.

Furthermore from the example it looks as if all this is going to
miss the scope to prevent sql injection since it doesn't support
prepared statements.


-- 
Ivan Sergio Borgonovo
http://www.webthatworks.it

Hi,

>  The problem may be legacy code.

Of course. There is a lot of legacy code that needs to be made secure
('hardened'). The best solution is to use parameterized queries. To
find out what statements are still not doing that, first disable text
literals only. If some places are incorrect, the relevant statements
will be in the log file. After text literals are fixed, number
literals can be disabled.

>  Since it is going to make dev nervous because it adds code bloat
>  that's going to cause more bugs than the SQL injections it may
>  prevent.

I don't think it will really bloat the code. In fact, the code will be
cleaner afterwards.

>  "select a.id, b.name from a join b on b.id=a.id where
>  a.status='pending' and b.id>7 and b.status='logged'

I even saw code like this in a VIEW: ... and b.type = 10430001 ... The
10430001 had a special meaning. It was documented somewhere, but not
in the code of course ;-) 'pending' and 'logged' are better, but in
regular programming languages usually constants are defined. This also
solves the 'disable literals' pain you have described. The code would
look like this:

select a.id, b.name from a join b on b.id=a.id where
a.status=STATUS_PENDING and b.id>? and b.status=STATUS_LOGGED.

So parameters only need to be used for the actual user input.

>  Prepared statements force you to match input with position and it is
>  definitively error prone.

The correctness of the application in the normal case is usually
tested. But I didn't so far see any SQL injection tests in regular
application.

>  Everything is still in the hands of the dev.

Not always, specially not in banking applications.

> you want to make your dev life a hell

Using parameterized queries is not 'hell', it's best practice.

Regards,
Thomas

On Sun, Apr 27, 2008 at 12:38 PM, Ivan Sergio Borgonovo
<mail@webthatworks.it> wrote:
> On Sat, 26 Apr 2008 21:50:10 -0600
>  "Scott Marlowe" <scott.marlowe@gmail.com> wrote:
>
>  > Agreed.  My point was that to do what the OP wants, wouldn't it make
>  > more sense to just lobotomize libpq so it doesn't understand
>  > anything but prepared queries.  Doesn't obviate the need for a
>  > client side language based solution.  Just seems to make WAY more
>  > sense than trying to make the change at the server level in pgsql.
>
>  The problem may be legacy code.
>
>  You'd like to statically point out places where multiple statements
>  could get injected.
>  All calls to your "query" function get routed to a wrapper that
>  actually call prepare/execute logic.
>  You do a BIG search&replace and see where your code fail cos you
>  actually needed more than one statement in a query.
>  Now you just have to grep your code for direct call to "plain"
>  queries during commit of your rcs.
>
>  My proposal was to add a switch that force routing to prepared
>  statement logic in libpq.
>
>  I'm thinking about situation in which you're using a library that
>  already wrap your query call.
>  You don't want to change the wrapper, so you don't want to take the
>  responsibility, sync troubles etc... of the library maintainer but
>  still you'd like to add a safety net to your code.
>
>  People dealing with your code would still see the familiar library
>  wrapper (you're not wrapping the wrapper) but you'd be able to switch
>  to "single statement mode".
>
>
>  Still ALLOW_LITERALS is a nice feature even if I think it won't fix
>  the notorious SQL injection problem forever.
>  Since it is going to make dev nervous because it adds code bloat
>  that's going to cause more bugs than the SQL injections it may
>  prevent.
>  Once you've developers that are so patient to write stuff like:
>
>  "select a.id, b.name from a join b on b.id=a.id where
>  a.status='pending' and b.id>7 and b.status='logged'"
>
>  into
>
>  "select a.id, b.name from a join b on b.id=a.id where
>  a.status=? and b.id>? and b.status=?", 'pending', 7, 'logged'
>
>  there are high chances they will prefer to spend some of their time
>  actually thinking about what they are writing.
>
>  I do know that thinking can't be taken for granted and that habits
>  and automatic methods may be generally preferable to "thinking", but
>  automatic methods works when they don't look painful.
>  Prepared statements force you to match input with position and it is
>  definitively error prone.
>
>  It is a tool... you may have some section of your code where that
>  parameter can't be changed, but most of the time you'll find it
>  useful if its default is set to NONE and dev *can* change it.
>
>  Now... let's think at the poor programmer...
>
>  He is writing a SQL statement that is static. He has to disable
>  ALLOW_LITERALS.
>  He is writing dynamic SQL that DON'T take user input.
>  ALLOW_LITERALS may still have some sense as a debugging tool but
>  there are high chances he will disable it to avoid other errors and
>  make coding simpler.
>  He is writing dynamic SQL that does take user input. He should be
>  forced to use ALLOW_LITTERALS NONE. But how can he be forced in the
>  middle of a program?
>  He is writing a "mixed" statement where some input is actually static
>  but not all... he may think it is easier to allow literals.
>
>  Everything is still in the hands of the dev.
>  Such setting may help you in static code evaluation since you may
>  spot easier the places where there could be breach of policy... but
>  still unless you want to make your dev life a hell... it is not going
>  to solve the SQL injection problem.
>
>  "mixed" statements that use external input and static input are quite
>  common and writing them avoiding literals may be a pain that your dev
>  won't be willing to suffer.
>
>  Queued statements in one query are far less common.
>
>  Still I do think that ALLOW_LITERAL is a valuable tool.
>  Same problems for legacy code apply.
>
>
>  --
>  Ivan Sergio Borgonovo
>  http://www.webthatworks.it
>
>
>  --
>
>
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>

Ivan Sergio Borgonovo wrote:
> That's better than nothing but it is still a lot of code duplication.
> You've to write column names in the sql statement and in the array
> and... column values are not contextual to the statement.
>   

The apparent duplication in the example stems for its tutorial nature. 
In a real program, the namedict "array" (it's actually a Python 
tuple--an immutable array) would normally be constructed 
programmatically from user or other input. Note also that although 
Joshua chose to use dictionary keys named identical to the PG column 
names, they could be named differently, like "first" and "last".
> That's easy... while what I wrote above does look as requiring a
> really special parser.
>
> Furthermore from the example it looks as if all this is going to
> miss the scope to prevent sql injection since it doesn't support
> prepared statements.
>   

I assume you didn't check the PEP 249 
(http://www.python.org/dev/peps/pep-0249/). The execute() and 
executemany() Cursor object methods are precisely to prepare and execute 
database operations.

Joe