Microsoft Edge: Default Flash click2play whitelist is insecure 

CVE-2019-0641


In Microsoft Windows, there is a file C:\Windows\system32\edgehtmlpluginpolicy.bin that contains the default whitelist of domains that can bypass Flash click2play and load Flash content without getting user confirmation in Microsoft Edge. This is a binary file containing multiple records and the format of each record is:
 - (32 bytes) sha256 hash of the domain name represented as a wide char string
 - (4 bytes) 32-bit permission flags describing in what cases Flash is allowed to load

On Windows 10 v1803 this file contains 58 records. By using a dictionary of known domain names, I managed to crack most of the domain names (56/58 to be exact). Following is the textual representation of edgehtmlpluginpolicy.bin in the format

hash:permissions:cleartext

01d004ae59fe9d0902b0e4526999432118199654f78b0384e4eb983e986d562d:3:<a href="http://www.pogo.com" title="" class="" rel="nofollow">www.pogo.com</a>
0309388894379c1e0d01081f6f4d5d4412a82dc5b9bd66476de2270b361cecfd:1:www.wasu.cn
0ae9eeba3229fa449ff5fcf42692cad2305e14933a6102187e94c48346ab8c9d:1:www.tvnow.de
0bc8e61a5970eb325f02148c05b79d60a9a0462efc18a6a60b7f8cd2dc84ccbc:1:chushou.tv
0bfc80d67c9b57f3f1bb978344c8d8d6ac19786e261f98c1c9735f6ba5ec344c:1:<a href="http://more2.starfall.com" title="" class="" rel="nofollow">more2.starfall.com</a>
1136593de37540f6f5396fdbbf93aa070c2b1c844d2d3d06de5373831a9df3bf:1:<a href="http://loa.gtarcade.com" title="" class="" rel="nofollow">loa.gtarcade.com</a>
12055be963e0f2c7786d1283d343afbaac921513a985a21f5f83b6a82b9582e9:1:<a href="http://nseindia.com" title="" class="" rel="nofollow">nseindia.com</a>
12c3d9b1a0a1f33a7d7ab1b4ccb53c1163210ee527ad5336175eb40ff1fcfe45:1:
2135e9b55346dd4146bbfae6f0cc896a39688d3287a952f63ae222837e5de152:1:<a href="http://www.wgt.com" title="" class="" rel="nofollow">www.wgt.com</a>
22af4cad3e57873a50693fe36d6385795ae6c56e4d0d759530f263db571a6b2c:1:netgauge.unitel.ao
2df0e6efc506a72a4c9e91ebebe70cf8252f1ffbd8b483043b1a856b75d13ce9:1:www.icourses.cn
2f87a652a9d2880a3ad580ec4a91bde3f4d2d32ac8f792d4258518d46330870f:1:www.la7.it
2f9f879f017ebe4d6f71a0755eee3b08a5f757c0d011112ded94e6b337b3b520:1:www.dgestilistas.es
348374ff89afe5693015c3d38758c83867c180a8010372a564c8f5eeaf9b5d0b:1:<a href="http://www.zxxk.com" title="" class="" rel="nofollow">www.zxxk.com</a>
3c23924f2f71c05d3b484fbaaa6e4ab4319d5bb3f0a002688132aa0f8434fd3b:1:weathernews.jp
46bdf3a01ab608d1a5e68923532e610ff7725a68d4bb063c96c8dedd4617404a:9:<a href="http://bigfarm.goodgamestudios.com" title="" class="" rel="nofollow">bigfarm.goodgamestudios.com</a>
4740f56f40ed20eddb576ae29fdf0c507dd06681e949bda8be5611eaf3ad9d3d:1:<a href="http://www.facebook.com" title="" class="" rel="nofollow">www.facebook.com</a>
4779eb7f42cc6736ca2b1e52449799705214f2542fa4cf952e741d8dd5efad31:1:<a href="http://www.deezer.com" title="" class="" rel="nofollow">www.deezer.com</a>
4f5db25a3bd2f1abf3dd1a509b2e1a6d81b9ba4428f333454c29d93e794150bc:1:
515563682e9bfc44b6fed4459149f83ba7f207bf53f6a0208156ac7c46e59d92:1:yahoo-mbga.jp
51bfa3e340a5ff7dfa37ad7ad409e5a214caadd0f82fc1fef82d38b766c2f088:1:ok.ru
563d53ee90b355ebd7558c2d9f3bee94489d406c565f9ed5741fb59bbc734544:1:<a href="http://seer.61.com" title="" class="" rel="nofollow">seer.61.com</a>
5b13e0a388860a0f136eefdd36d2f57fb81f46588ca85e7d93a4fd24cf6462f8:9:<a href="http://empire.goodgamestudios.com" title="" class="" rel="nofollow">empire.goodgamestudios.com</a>
5e7fc524d10f21da23bc43f24de00967094d69d6f4ccda277fff7042024c3ce5:1:<a href="http://www.friv.com" title="" class="" rel="nofollow">www.friv.com</a>
5f832e1442b497050d79cd18b32de807e4201a3181929ade823112defa6c1079:1:<a href="http://video.baomihua.com" title="" class="" rel="nofollow">video.baomihua.com</a>
64e2991629e5e208874400bc1ea0161fb064f1c2397b1cedc3bb282ea3f4ee3b:1:<a href="http://hiztesti.turktelekom.com" title="" class="" rel="nofollow">hiztesti.turktelekom.com</a>.tr
6793b64c0ccc547a01b8b6982318e25ae3dc0b91dfc09366c7f1f1b3a7fa127e:1:<a href="http://www.scholastic.com" title="" class="" rel="nofollow">www.scholastic.com</a>
68fc10e638f0bb2e25149d2ef8d3d87cf318bbf2de7c9aa74131d53e926fe79e:1:<a href="http://www.viz.com" title="" class="" rel="nofollow">www.viz.com</a>
881bcca2199248b7c82ed14cb1dbd6e87ac9ea899d1f9f02d13d29e837487782:1:www.dilidili.wang
89ac7d2d82b6a2ef952e3d627853180fb250167ed56b893647814e8374d4f5cd:1:<a href="http://games.aarp.org" title="" class="" rel="nofollow">games.aarp.org</a>
900da7ee51cf43450699d9cd11e3cf6ba8d2d04d9d836cd359281d7791e328af:1:<a href="http://www.douyu.com" title="" class="" rel="nofollow">www.douyu.com</a>
9adea347b4e793529c9a5e1a35e2aa7c88772b7e2a086d2d24a4f8ccbb20e3ac:1:<a href="http://rc.qzone.qq.com" title="" class="" rel="nofollow">rc.qzone.qq.com</a>
9c97a59b30e879d3245139795adea4380f62e4e14149025f12f69eb3b532e518:1:www.nicovideo.jp
a2cf2fe6a8822459d81d15b1327b5bac601bafc460fafa716bc2dcc21e9ab50e:1:<a href="http://www.mynet.com" title="" class="" rel="nofollow">www.mynet.com</a>
a77de76633b0717c62034512fb5c3fbb50633ad9b5ebef7a8acf180e455a3025:1:<a href="http://www.hotstar.com" title="" class="" rel="nofollow">www.hotstar.com</a>
ad973e7d68dd2c1a8e9f04886e34db40021e1e76eff3bbc53e7ab8934688a4ed:1:<a href="http://www.4399.com" title="" class="" rel="nofollow">www.4399.com</a>
b61f47eb2fc64b2ad7ee4ae780ea0ac1a886b4f02f1ec8da77db13f920b4874b:1:<a href="http://www.bilibili.com" title="" class="" rel="nofollow">www.bilibili.com</a>
ba33c2367ea9f0c66b5b3f345be68a0287a96ca797654c0bf9b2e584d2809ccb:1:<a href="http://www.msn.com" title="" class="" rel="nofollow">www.msn.com</a>
ba3bc78ec1f427cba6e22cbd63dae305814ca0f0740c0dbd494f804fcaef671a:1:<a href="http://zone.msn.com" title="" class="" rel="nofollow">zone.msn.com</a>
c2fda282c3b5875eaeb6d27ecf62b995684d5739ba1e4082d265dd28dd98ef70:1:<a href="http://www.worldsurfleague.com" title="" class="" rel="nofollow">www.worldsurfleague.com</a>
ca6efef88504373a9406ed9a31b430d6df8bb60ea630ac698b0d7c4dab0faf7a:1:<a href="http://www.stupidvideos.com" title="" class="" rel="nofollow">www.stupidvideos.com</a>
d833be74b7f95eb0ac133c5aa06c71b7792b5051b1a369740694e78525a4d872:4:<a href="http://entitlement.auth.adobe.com" title="" class="" rel="nofollow">entitlement.auth.adobe.com</a>
dd0f56a6b1a1f2908f4ff45438ffa5e05679375ed0aade8e3ab36bf4c0bd40f4:1:<a href="http://video.fc2.com" title="" class="" rel="nofollow">video.fc2.com</a>
dd2ab62df5da52e66844171efc4415a087cc1a8c432312d814a62da582f40e2d:1:www.ontvtime.ru
ddf38cb97def571ec55f58d372db15fe6ee01578adc85b1087823d239d758af8:1:<a href="http://apps.facebook.com" title="" class="" rel="nofollow">apps.facebook.com</a>
e2f07d2fb0e6beac78d55962dda9ebcedba6c3ba30bf83b0880fae69d29537bf:1:<a href="http://www.totaljerkface.com" title="" class="" rel="nofollow">www.totaljerkface.com</a>
e35635613116ae9266c41348d2f4978f093c2fe75ae91f010ad23c1be31b833c:1:<a href="http://www.hungamatv.com" title="" class="" rel="nofollow">www.hungamatv.com</a>
e39ce3cd42a88216ff9060e8b136bdc153f52322f259321a5925e629659684f8:1:<a href="http://edu.glogster.com" title="" class="" rel="nofollow">edu.glogster.com</a>
e4003a967100eb3a92e9148a51e7cd302e6ca4bcc34566c671378a4b0756ef66:1:<a href="http://v.pptv.com" title="" class="" rel="nofollow">v.pptv.com</a>
e4dcd660eae7eeb1ea42050b6dcb108a9bedf1a66e3791438c6abe1efc907e1b:1:life.pigg.ameba.jp
e57c8c0083d4ea6fb4b390682d8ad3dffaeda2d37d1c11b9d29418b4a318e1a9:1:www.panda.tv
e7bce4b54da6dda25cabbe9da2359fe2833c94ec1ce3edd67077a089ed76ef31:1:<a href="http://www.vudu.com" title="" class="" rel="nofollow">www.vudu.com</a>
e9ce06c9a6a05878802f64fac17399cc0a8452c652403445995a90dc9b19401d:1:<a href="http://www.nseindia.com" title="" class="" rel="nofollow">www.nseindia.com</a>
ef7f6be560fb99cff749ac35415beeed4aa86f40e10138858289dde1284661c9:1:<a href="http://music.microsoft.com" title="" class="" rel="nofollow">music.microsoft.com</a>
f2313491b771d1180f9c4e9cf979820e276a7833859555976dbf4a529cb2189f:1:<a href="http://en.ikariam.gameforge.com" title="" class="" rel="nofollow">en.ikariam.gameforge.com</a>
f4f46a8b3a55ffb3e3784e6743266ed8d7cd2fdd21f494a82e2772fc68590d1b:1:www.deraktionaer.tv
fcb0eec77983791a7eeb971a2320f38cdbac2ca16cf3f418f83a00a4338eafd4:1:<a href="http://www.a1.net" title="" class="" rel="nofollow">www.a1.net</a>
fee3af1754656ed83ba706b46c6fa570b020ff79ad84b5adee4882fbf6adaf0e:1:<a href="http://www.poptropica.com" title="" class="" rel="nofollow">www.poptropica.com</a>

As can be seen from the cleartext domain names, the list is pretty broad and contains a lot of sites that at least I personally wouldn't expect to find on such a whitelist.

The most common permission flag value (1) indicates that the site is allowed to load Flash content if:
a) the Flash content is hosted on the same domain *OR*
b) The element containing Flash is larger than 398x298 pixels
as can be seen in FlashClickToRunHelper::DetermineControlAction

This whitelist is insecure for multiple reasons:
 - An XSS vulnerability on any of the domains would allow bypassing click2play policy.
 - There are already *publicly known* and *unpatched* instances of XSS vulnerabilities on at least some of the whitelisted domains, for example <a href="https://www.openbugbounty.org/reports/582253/" title="" class="" rel="nofollow">https://www.openbugbounty.org/reports/582253/</a> and <a href="https://www.openbugbounty.org/reports/444528/" title="" class="" rel="nofollow">https://www.openbugbounty.org/reports/444528/</a> and <a href="https://www.openbugbounty.org/reports/130555/" title="" class="" rel="nofollow">https://www.openbugbounty.org/reports/130555/</a>
 - The whitelist is not limited to https (this wouldn't work anyway as some of the whitelisted domain don't support https at all). Even in the absence of an XSS vulnerability, this would allow a MITM attacker to bypass the click2play policy.


This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available (whichever is earlier), the bug
report will become visible to the public.



Found by: ifratric