Sunday, February 13, 2011

Taming the Beast

The recent cross-platform numerical parsing DOS bug has been named the "Mark of the Beast". Some claim that this bug was first reported as early as 2001.

This is a significant bug in (at least) PHP and Java. Similar issues have effected Ruby in the past. This bug has left a number of servers, web frameworks and custom web applications vulnerable to easily exploitable Denial of Service.

Oracle has patched this vuln but there are several non-Oracle JVM's that have yet to release a patch. Tactical patching may be prudent for environment.

Here are three filters that may help you tame this beast of a bug.

1) Ryan Barnett deployed a series of mod security rules and documented several options here

2) Bryan Sullivan from Adobe came up with the following Java-based blacklist filter. This rule is actually quite accurate in *rejecting input* in the DOSable JVM numeric range. This fix, while simple, does indeed reject a series of normally good values.

public static boolean containsMagicDoSNumber(String s) {
return s.replace(".", "").contains("2225073858507201");

3) The following data sanitization code came from Brian Chess at HP/Fortify. This approach detects the evil range before trying to call parseDouble and returns the IEEE official value for any double in this most evil range ( 2.2250738585072014E-308 ).

private static BigDecimal bigBad;
private static BigDecimal smallBad;

static {
BigDecimal one = new BigDecimal(1);
BigDecimal two = new BigDecimal(2);
BigDecimal tiny = one.divide(two.pow(1022));
// 2^(-1022) ­ 2^(-1076)
bigBad = tiny.subtract(one.divide(two.pow(1076)));
//2^(-1022) ­ 2^(-1075)
smallBad = tiny.subtract(one.divide(two.pow(1075)));

public static Double parseSafeDouble(String input) throws InvalidParameterException {

if (input == null) throw new InvalidParameterException("input is null");

BigDecimal bd;
try {
bd = new BigDecimal(input);
} catch (NumberFormatException e) {
throw new InvalidParameterException("cant parse number");

if (bd.compareTo(smallBad) >= 0 && bd.compareTo(bigBad) <= 0) {
// if you get here you know you're looking at a bad value. The final
// value for any double in this range is supposed to be the following safe #
//return safe number
System.out.println("BAD NUMBER DETECTED - returning 2.2250738585072014E-308");
return new Double("2.2250738585072014E-308");

//safe number, return double value
return bd.doubleValue();

Sunday, January 9, 2011

Touchpoints and BSIMM hurt AppSec

Conjecture: BSIMM and Touchpoints are harmful to developers and organizations seeking cost effective application security based risk reduction.

Let’s start with the flaws of Touchpoints:

1. Touchpoints make security separate from development
2. Touchpoints are all verification, not build secure apps
3. Touchpoints are only SDLC (one app), not full boar appsec program planning across an entire application portfolio
4. Touchpoints makes security a cost, not an opportunity for improvement in other aspects of software dev
5. Touchpoints are negative vulnerability focused, not positive controls centric thinking
6. Touchpoints are basically hacking ourselves secure, not assurance evidence based
7. Touchpoints are trivial in the sense that they are just a concept with no backing... just a picture and a book. No meat!
8. Touchpoints are designed to sell tools - not totally, but somewhat
9. Touchpoints are not free and open (creative commons anyone?)

BSIMM continues with this tradition.

Does your organization really care if the software you are writing is secure, or is it a burden and a chore? No amount of process will fix not caring. BSIMM does almost nothing to create a culture of good security practices for developers. It’s again, 80% verification activities. It extends the tradition of the Touchpoints model which was 100% verification.

BSIMM and touchpoints do not go down and dirty to figure out how to actually make software secure.

And frankly, that’s what the entire world really needs right now.