[Esapi-user] ESAPI Random Number Generation Broken

Jim Manico jim.manico at owasp.org
Sat Jun 28 05:34:51 UTC 2014


One more note, this really was a serious ESAPI bug and all current
versions really are vulnerable, especially the CSRF protection. Should
we consider requesting/reporting a CVE for this?

Aloha,
--
Jim Manico
@Manicode
(808) 652-3805

> On Jun 28, 2014, at 3:28 AM, "Kevin W. Wall" <kevin.w.wall at gmail.com> wrote:
>
> W00t! Alright Jeff. Great job.
> Thanks for the assist and doing the heavy lifting.
>
> -kevin
> P.S.- I haven't tested it yet, but I will and I trust your results.
> Busy w/ other things right now.
>
> On Fri, Jun 27, 2014 at 10:16 PM, Jeff Williams
> <jeff.williams at aspectsecurity.com> wrote:
>> Everyone,
>>
>> I found the problem.  The real problem.  There was a change introduced in StringUtilities r722 that broke the union() method.  This method was used to generate the EncoderConstants.CHAR_ALPHANUMERICS set used in the test case.
>>
>> I've checked in a fix and test cases to verify that it works.  I also added a very simple test case for getRandomString() that verifies that the method generates roughly the same number of each character across a bunch of generated strings.  Not perfect but at least sensitive enough to recognize if something is way off.
>>
>> The good news is that order has been restored to the universe, and our Burp test suite results are back to 'excellent'.  If you'd like to verify this yourself (and I strongly encourage you to do so) I included a small utility to generate random tokens as a main() method in RandomizerTest.
>>
>>    /**
>>     * Run this class to generate a file named "tokens.txt" with 20,000 random 20 character ALPHANUMERIC tokens.
>>     * Use Burp Pro sequencer to load this file and run a series of randomness tests.
>>     *
>>     * NOTE: be careful not to include any CRLF characters (10 or 13 ASCII) because they'll create new tokens
>>     * Check to be sure your analysis tool loads exactly 20,000 tokens of 20 characters each.
>>     */
>>        public static void main(String[] args) throws IOException {
>>                FileWriter fw = new FileWriter("tokens.txt");
>>                for (int i = 0; i < 20000; i++) {
>>                        String token = ESAPI.randomizer().getRandomString(20, EncoderConstants.CHAR_ALPHANUMERICS);
>>                        fw.write(token + "\n");
>>                }
>>                fw.close();
>>        }
>>
>> Thanks to everyone who put some thought into the issue.
>>
>> --Jeff
>>
>>
>> -----Original Message-----
>> From: Jim Manico [mailto:jim.manico at owasp.org]
>> Sent: Thursday, June 26, 2014 1:30 AM
>> To: Kevin W. Wall
>> Cc: Jeff Williams; Bruno Girin; esapi-dev at lists.owasp.org; esapi-user at lists.owasp.org
>> Subject: Re: [Esapi-user] ESAPI Random Number Generation Broken
>>
>> I'll track these issues on google code as soon as I get to a real computer. Everything you say makes perfect sense to me and I appreciate your time.
>>
>> I'm still going to chase down DJB's SecureRandom hack for our analysis. (Dr) Steven Murdoch is here in Cambridge and made that suggestion.
>>
>> Cheers, Kevin.
>> --
>> Jim Manico
>> @Manicode
>> (808) 652-3805
>>
>>>> On Jun 26, 2014, at 5:39 AM, "Kevin W. Wall" <kevin.w.wall at gmail.com> wrote:
>>>>
>>>> On Wed, Jun 25, 2014 at 9:57 AM, Jim Manico <jim.manico at owasp.org> wrote:
>>>> PS: Java 8 improves upon this and provides a new API:
>>>> http://docs.oracle.com/javase/8/docs/api/java/security/SecureRandom.h
>>>> tml#getInstanceStrong-- which is what we should be using for "
>>>> high-value/long-lived secrets like RSA public/private keys". But even
>>>> then, using the same instance without reseeding with lead to a PRNG,
>>>> not a CRNG sequence.
>>>
>>> That's all well and good, but even with JDK 7 and earlier,
>>> SecureRandom
>>> *is* a CSRNG. (Note that a CSRNG *is* a PRNG.)  The problems with
>>> SecureRandom very early own is that they just punted on the initial
>>> pseudo-random seed. Before JDK 1.4 (I think that's where it was
>>> changed), the first time they set the seed, they did some black magic
>>> like mixing together a few bits from the current time in milliseconds,
>>> the current amount of total and available memory in the Java heap, and
>>> added in how many times a thread could yield in 3 seconds.  Near boot
>>> time, all those things were very predictable. In 1.4 (maybe 1.3), it
>>> was changed to initialize the seed /dev/urandom if it was available
>>> and if not, I think it reverted to some other song and dance.  There
>>> is problems however with /dev/urandom shortly after boot time (and
>>> ESPECIALLY shortly after the *initial* system boot). Using /dev/random
>>> would be better, but unfortunately that will block. (Aside: At my
>>> previous job, we wrote an EntropyPool to seed things like SecureRandom
>>> that would read from /dev/random by default or alternately
>>> /dev/urandom. There was a warning in the Javadoc if would block and to
>>> use the weaker entropy setting if that was a concern. It was never a
>>> problem until one time when an application had a new release and they
>>> started requesting [for some unknown reason] about 10k worth of data
>>> from this EntropyPool all at once. And it was in an /etc/init.d script
>>> that started their application in WebLogic Server. Result was they had
>>> a 20+ minute startup delay until 10k bytes could be collected from
>>> /dev/random. They called me in the middle of the night to 'yell' at
>>> me. I nicely told them to RTFM. Sigh.)
>>>
>>> Anyway, my guess is that getInstanceStrong() method will allow you to
>>> specify things like "use /dev/random".  However, I agree with Thomas
>>> Ptacek's comment that if it really matters use an Operating
>>> System-level CSRNG and not a userspace CSRNG. There are of course
>>> reasons why you might not want to. Always using /dev/urandom is a
>>> reasonable compromise, but there are still edge cases where you can
>>> get burned by using /dev/urandom rather than /dev/random. But unless
>>> you are protecting nuclear launch codes (and seriously, you BETTER not
>>> be doing that with Java since you can't guarentee that you clear
>>> memory), /dev/urandom will probably suffice.
>>>
>>> Also, one thing that I picked up on the Cigital blog post
>>> (http://www.cigital.com/justice-league-blog/2009/08/14/proper-use-of-j
>>> avas-securerandom/) was that an attacker could potentially hide a call
>>> like this
>>>
>>>   System.setProperty("securerandom.source", "/dev/zero");
>>>
>>> in some 3rd party library that you are using and then your are toast.
>>> Of course, the same is true if you don't specify that you want the Sun
>>> provider as in:
>>>
>>>   SecureRandom csrng = SecureRandom.getInstance("SHA1PRNG", "SUN");
>>>
>>> as someone could dynamically insert their own tainted provider for
>>> SecureRandom into a 3rd party library you are using and again you are
>>> screwed. (Unless of course you are using a Java SecurityManager and an
>>> appropriately locked-down security policy which I am sure that you
>>> *all* are doing, right. Cough, cough.)
>>>
>>> Anyhow, we need to do something about those two things in ESAPI...
>>> especially the first since it would be really subtle. Anyone care to
>>> write up a Google issue to that effect to remind me?
>>>
>>> Cheers,
>>> -kevin
>>> --
>>> Blog: http://off-the-wall-security.blogspot.com/
>>> NSA: All your crypto bit are belong to us.
>
>
>
> --
> Blog: http://off-the-wall-security.blogspot.com/
> NSA: All your crypto bit are belong to us.


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