Critical Vulnerabilities in JSON Web Token Libraries

Be wary if you do anything with signed data before you verify the signature.<p><a href="http:&#x2F;&#x2F;www.thoughtcrime.org&#x2F;blog&#x2F;the-cryptographic-doom-principle&#x2F;" rel="nofollow">http:&#x2F;&#x2F;www.thoughtcrime.org&#x2F;blog&#x2F;the-cryptographic-doom-prin...</a>

By the way, claps for Tim for the amazing job. He contacted various people and gave them heads up weeks ago. I think the wat this was handled was awesome.<p>&lt;3 OSS

I don&#x27;t understand why you need the alg property at all. I mean, you are the one issuing the token so you definitely know what algorithm is used in the back-end. Why is this necessary?

I found a (thematically) similar issue in the clojure jwt library last year [1]. Now I&#x27;m wondering if the issue may be wider than just that library.<p>[1] <a href="https:&#x2F;&#x2F;github.com&#x2F;liquidz&#x2F;clj-jwt&#x2F;issues&#x2F;8" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;liquidz&#x2F;clj-jwt&#x2F;issues&#x2F;8</a>

Also see: <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=9111049" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=9111049</a><p>Where are the CVEs?! ... OK, I just sent a brief write-up to the oss-security list, we&#x27;ll see what happens.

I&#x27;m glad someone of not finally made a statement about that. I have reported two bugs like this against libraries in the last two years and the general feedback has been, that it&#x27;s not an issue. They just removed the none algorithm entirely.

For those of you concerned about if a JWT library you&#x27;re using is vulnerable, you can see the current list of verified&#x2F;validate clients for each language here: <a href="http:&#x2F;&#x2F;jwt.io&#x2F;" rel="nofollow">http:&#x2F;&#x2F;jwt.io&#x2F;</a> (page down to see the list)<p>My team has been using ruby-jwt, so I&#x27;m glad to see that at least does not seem to be on the list of vulnerable libraries.

I&#x27;ve actually seen this same issue in JWT libs before (August 2014) as well. I think one of the main issue is JWT is simple to implement, the specification seems to be unclear about how to treat unsecure JWTs (with the `none` alg).<p>From the specificaiton: Even if a JWT can be successfully validated, unless the algorithm(s) used in the JWT are acceptable to the application, it SHOULD reject the JWT.<p>So what it is saying is that you should have code in your application to make sure to only trust algorithms that you like.<p>The other issue is that following the specifications rules for validation get you in a hairy spot where this vulnerability exist:<p><a href="https:&#x2F;&#x2F;tools.ietf.org&#x2F;html&#x2F;draft-ietf-oauth-json-web-token-32#section-7.2" rel="nofollow">https:&#x2F;&#x2F;tools.ietf.org&#x2F;html&#x2F;draft-ietf-oauth-json-web-token-...</a>

Can someone please explain to me the appeal of tokens like the following please?<p><pre><code> payload = &#x27;{&quot;loggedInAs&quot;:&quot;admin&quot;,&quot;iat&quot;:1422779638}&#x27; </code></pre> I&#x27;ve always worked under the assumption that everything the client sends is wrong; which means the only fields I issue are a user hash and session key. If either of those don&#x27;t match the session table record then the token is rejected. Having group permissions issued from the client side seems like a bad design from the offset - however this seems a really obvious point to make, which makes me wonder if I&#x27;m missing the point of JWT&#x27;s.<p>Is anyone able to expand on this for me please?

If you love to confirm your stereotypes as much as the next guy, take a closer look at the languages:<p>- Ruby, Java, Lua, Scala and .NET are unaffected<p>- updates are available for Node.js and Python<p>- there are still no fixed version for JavaScript and PHP libs

They list the php-jwt library from firebase as vulnerable but I can&#x27;t see why. As far as I can see they do not support the None algorithm.<p><a href="https:&#x2F;&#x2F;github.com&#x2F;firebase&#x2F;php-jwt&#x2F;blob&#x2F;master&#x2F;Authentication&#x2F;JWT.php" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;firebase&#x2F;php-jwt&#x2F;blob&#x2F;master&#x2F;Authenticati...</a><p>It&#x27;s not in the methods array and the decode method specifically does a check to see if it&#x27;s empty.<p>if (empty($header-&gt;alg)) { throw exception }<p>Can anyone throw some light on this?

Don&#x27;t use JSON Web Tokens.

Original, non-spam source is:<p><a href="https:&#x2F;&#x2F;www.timmclean.net&#x2F;2015&#x2F;03&#x2F;31&#x2F;jwt-algorithm-confusion.html" rel="nofollow">https:&#x2F;&#x2F;www.timmclean.net&#x2F;2015&#x2F;03&#x2F;31&#x2F;jwt-algorithm-confusion...</a>