Firefox Denial Of Service

🗓️ 29 May 2009 00:00:00Reported by Thierry ZollerType
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Firefox Denial Of Service (KEYGEN) design bug causes endless loop and memory leaks, impacting user input and browser access
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From the very-low-hanging-fruit-department  
Firefox Denial of Service (KEYGEN)  
________________________________________________________________________  
  
  
Release mode: Forced release.  
Ref : [TZO-27-2009] - Firefox Denial of Service (KEYGEN)  
WWW : http://blog.zoller.lu/2009/04/advisory-firefox-denial-of-service.html  
Vendor : http://www.firefox.com  
Status : No patch  
CVE : none provided  
Credit : none   
Bugzilla entry: https://bugzilla.mozilla.org/show_bug.cgi?id=469565  
  
Security notification reaction rating : There wasn't any appropriate reaction.   
Notification to patch window : x+n  
  
Disclosure Policy : http://blog.zoller.lu/2008/09/notification-and-disclosure-policy.html  
  
Affected products :   
- Firefox 3.0.10 (Windows)  
- Likely : All Firefox versions supporting the KEYGEN tag.  
  
I. Background  
~~~~~~~~~~~~~  
Firefox is a popular Internet browser from the Mozilla Corporation. In 2007 the  
Mozilla Corporation had a revenue of over 75 million dollars [1], out of   
which 68 million where made with a search advertising deal, in other words with  
the search box in Firefox that defaults to Google.  
  
I envy the spirit of everyone that works on Firefox code in their spare time,   
for free.   
  
II. Description  
~~~~~~~~~~~~~~~  
This bug is a simple design bug that results in an endless loop (and interesting  
memory leaks).  
  
Once upon a time Netscape thought it would be a great idea to add the keygen tag  
(<keygen>) as a feature to their Browser. The keygen tag offers a simple way  
of automatically generating key material using various algorithms. For instance  
it is possible to generate RSA, DSA and EC key material.  
  
"The public key and challenge string are DER encoded as PublicKeyAndChallenge and   
then digitally signed with the private key to produce a SignedPublicKeyAndChallenge.   
The SignedPublicKeyAndChallenge is base64 encoded, and the ASCII data is finally   
submitted to the server as the value of a name-value pair, where the name is   
specified by the NAME attribute of the KEYGEN tag."   
  
More information: https://developer.mozilla.org/En/HTML/HTML_Extensions/KEYGEN_Tag  
  
This feature includes the automatic submission of the public part to a script,   
the crux. The Keygen tag reloads the document by submitting the public key as an argument  
to the current URI. Combining this with a javascript body onload() call  
(or meta refresh) results in an neat endless loop blocking access to the UI.  
  
Furthermore memory is leaked during the process.  
  
III. Impact  
~~~~~~~~~~~  
The browser doesn't respond any longer to any user input, tabs are no   
longer accessible, your work if any might be lost. Restarting the  
Firefox process and restoring the previous Firefox session will  
re-spawn the tab and start the loop again.  
  
According to a Bugzilla entry memory is also leaked during the process.  
  
So let's recap, we have a function that generates key material and looping  
causes memory to leak. One might think this should be important enough   
to investigate, especially if you know that for DSA for instance, only  
a few bits of k can reveal an entire private key. [3]   
  
Note: I am not saying the memory leaks include key material, seeing the lack  
of interest this bugzilla ticket triggered, I have not considered investigating   
further. What I am saying is that if security is taken seriously  
memory leaks that directly or indirectly happen during key generation  
need to be investigated thoroughly.  
  
  
IV. Proof of concept (hold your breath)  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
<html>  
<body onLoad="document.forms[0].submit()">  
<FORM>  
<KEYGEN NAME="somekey" CHALLENGE="1125983021">  
<INPUT TYPE="submit" NAME="SubmitButton" VALUE="Done">  
</FORM>  
</html>  
  
Live : http://secdev.zoller.lu/ff_dos_keygen.html  
  
  
IV. Disclosure timeline  
~~~~~~~~~~~~~~~~~~~~~~~~~  
DD/MM/YYYY  
14/12/2008 : Created bugzilla entry (security) with (the wrong) proof of concept  
file.  
  
14/12/2008 : Attached the correct POC file (mea culpa) and a stack trace and details  
of memory corruption that repeatedly occurred during testing the POC  
  
24/12/2008 : [email protected] comments : "I can definitely confirm the denial   
of service aspect, and there's a very minor memory leak (after 9   
hours of CPU time memory use went from 60MB to 360MB). Haven't been  
able to reproduce a crash."  
  
27/05/2009 : The 4 month grace period [2] given is reached. Release of this advisory.  
  
  
[1] http://www.mozilla.org/foundation/documents/mf-2007-audited-financial-statement.pdf  
http://www.guidestar.org/FinDocuments//2007/200/097/2007-200097189-047bbaa9-9.pdf  
[2] http://blog.zoller.lu/2008/09/notification-and-disclosure-policy.html  
[3] http://rdist.root.org/?s=dsa  
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29 May 2009 00:00Current
7.4High risk
Vulners AI Score7.4