A mighty fortress is our PKI

Peter Gutmann pgut001 at cs.auckland.ac.nz
Thu Jul 22 03:48:24 EDT 2010


Readers are cordially invited to go to https://edgecastcdn.net and have a look 
at the subjectAltName extension in the certificate that it presents.  An 
extract is shown at the end of this message, this is just one example of many 
like it.  I'm not picking on Edgecast specifically, I just used this one 
because it's the most Sybilly certificate I've ever seen.  You'll find that 
this one Sybil certificate, among its hundred-and-seven hostnames, includes 
everything from Mozilla, Experian, the French postal service, TRUSTe, and the 
Information Systems Audit and Control Association (ISACA), through to 
Chainlove, Bonktown, and Dickies Girl (which aren't nearly as titillating as 
they sound, and QuiteSFW).  Still, who needs to compromise a CA when you have 
these things floating around on multihomed hosts and CDNs.

Ian Grigg pointed out that this is also an EV certificate, I'm guessing that 
CDNs and multihomed hosts run into the same system-high problem that dogged 
MLS systems in the 1980s, they have to use the certificate at the highest 
level of any of the constituent domains.  So if you compromise (say) 
inpath-static.iseatz.com (which consists of a page that says "We're sorry, but 
something went wrong") or images.vrbo.com ("Directory Listing Denied") then 
you have an EV-validated site.  So the overall EV security becomes that of the 
least secure co-hosted domain.

I've tried connecting to the above site with HTTPS and get a normal non-EV 
Sybil certificate even though it's rooted in an EV CA... well, pseudo-rooted, 
the "root" is then signed by an old Entrust certificate, and the certificate 
itself is another multi-domain one, for Delta, Amtrak, Air France, KLM, Alaska 
Air, and others.  I wonder if they have some context-specific way to override 
EV on a per-site basis when it's used with Sybil certificates?  At the moment 
it's rather hard to test because depending on where you are in the world you 
get different views of servers and certificates (for example when I connect to 
ISACA, which is an EV site, I get a standard non-Sybil certificate that's only 
valid for ISACA), and finding a particular hostname in a Sybil certificate 
doesn't mean that you'll see that particular certificate when you connect to 
the server.

(Again, not wanting to pick on ISACA here, but finding a security audit 
organisation sharing a certificate with Dickies Girl is kinda funny.  You'd 
think there'd be a security audit process to catch this :-).

What a mess!  A single XSS/XSRF/XS* attack, or just a plain config problem,
and the whole house of cards comes down.

(For the TLS folks, SNI (a client-supplied Server Name Indication when it 
 connects) won't fix this because (a) it's not widely-enough supported yet and 
 (b) the server admin would have to buy 107 separate certificates to do the 
 job that's currently done by one Sybil certificate, and then repeat this for 
 every other Sybil certificate they use).

 666 2633:         SEQUENCE {
 670    3:           OBJECT IDENTIFIER subjectAltName (2 5 29 17)
 675 2624:           OCTET STRING, encapsulates {
 679 2620:             SEQUENCE {
 683   15:               [2] 'edgecastcdn.net'
 700   18:               [2] 'ne.edgecastcdn.net'
 720   21:               [2] 'minitab.fileburst.com'
 743   30:               [2] 'cdn.montimbrenligne.laposte.fr'
 775   27:               [2] 'zeroknowledge.fileburst.com'
 804   23:               [2] 'images.goldstarbeta.com'
 829   25:               [2] 'radialpoint.fileburst.com'
 856   19:               [2] 'wac.edgecastcdn.net'
 877   22:               [2] 'ne.wac.edgecastcdn.net'
 901   19:               [2] 'images.goldstar.com'
 922   15:               [2] 'images.vrbo.com'
 939   12:               [2] 'cdn.vrbo.com'
 953   18:               [2] 'content.truste.com'
 973   13:               [2] 'e1.boxcdn.net'
 988   13:               [2] 'e2.boxcdn.net'
1003   13:               [2] 'e3.boxcdn.net'
1018   25:               [2] 'privacy-policy.truste.com'
1045   13:               [2] 'www.sonos.com'
1060   19:               [2] 'www.dickiesgirl.com'
1081   26:               [2] 'static-cache.tp-global.net'
1109   29:               [2] 'images.homeawayrealestate.com'
1140   14:               [2] 'cdn.verint.com'
1156   13:               [2] 'swf.mixpo.com'
1171   21:               [2] 'cdn.traceregister.com'
1194   14:               [2] 's.tmocache.com'
1210   17:               [2] 's.my.tmocache.com'
1229   23:               [2] 'ne1.wpc.edgecastcdn.net'
1254   23:               [2] 'gp1.wpc.edgecastcdn.net'
1279   23:               [2] 'gs1.wpc.edgecastcdn.net'
1304   23:               [2] 'ne1.wac.edgecastcdn.net'
1329   23:               [2] 'gp1.wac.edgecastcdn.net'
1354   23:               [2] 'gs1.wac.edgecastcdn.net'
1379   24:               [2] 'c1.socialcastcontent.com'
1405   21:               [2] 'www.steepandcheap.com'
1428   22:               [2] 'www.whiskeymilitia.com'
1452   17:               [2] 'www.chainlove.com'
1471   16:               [2] 'www.tramdock.com'
1489   16:               [2] 'www.bonktown.com'
1507   16:               [2] 'www.brociety.com'
1525   15:               [2] 'www.mozilla.com'
1542   22:               [2] 'resources.homeaway.com'
1566   21:               [2] 'ssl-cdn.sometrics.com'
1589   35:               [2] 'cache.vehicleassets.captivelead.com'
1626   17:               [2] 'static.woopra.com'
1645   20:               [2] 'images.cardstore.com'
1667   15:               [2] 'images.ink2.com'
1684   32:               [2] 'resources.homeawayrealestate.com'
1718   18:               [2] 'cdn1.adadvisor.net'
1738   24:               [2] 'www.pictureitpostage.com'
1764   26:               [2] 'images.vacationrentals.com'
1792   34:               [2] 'serviceportal.carestreamhealth.com'
1828   23:               [2] 'assets-secure.razoo.com'
1853   29:               [2] 'resources.vacationrentals.com'
1884   23:               [2] 'download.entraction.com'
1909   12:               [2] 'ec.pond5.com'
1923   21:               [2] 'images.esellerpro.com'
1946   15:               [2] 'use.typekit.com'
[etc]

Peter.

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