Date: Tue, 10 Mar 2015 19:11:41 +0000 From: Marek Kroemeke <kroemeke@...il.com> To: cve-assign@...re.org Cc: oss-security@...ts.openwall.com Subject: Re: Varnish 4.0.3 heap-buffer-overflow while parsing backend server HTTP response. Hi there, It sounds like the same discussion that we had - we tried to avoid it by adding that last line of the report *cough* ;-) You don't need DNS spoofing - a php script which returns required "rouge" headers is enough right? When reporting the previous bugs, the thinking was more about cases like : * CDNs using varnish (in the same way cloudflare uses nginx, akamai uses "ghost" etc...) * Shared hosting environments that put varnish in front * Cases where backend app's response splitting bug is escalated to DoS or in this case, possibly to have RCE on server in between the client and the backend app. * Cases where you have backends with different level of "trust" And again - it all depends on how you treat reverse proxy server. Our understanding is that rfc doesn't specify or describe "reverse http proxy" , and essentially this can be treated as a server (when looking from browser perspective) or a client when looking from the backend server perspective. Question was - is a case where "client" may end up in in that undefined state (DoS , RCE due to some buffer overflow..) be treated as a security problem. Conclusion was that DoS is acceptable, not sure what about other types of bugs though. To be clear - we think that if vendor clearly says that you have to fully trust your backend server when you use the product, then this is what it is, but we can't/couldn't find anything like that on vendor's website (should we? - don't know, open question). regards, On Tue, Mar 10, 2015 at 02:21:26PM -0400, cve-assign@...re.org wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > > Our understanding after previous reports is that varnish security model assumes full > > trust of the backend, so this is not considered a security problem > > We'll try to infer CVE inclusion based on: > > http://openwall.com/lists/oss-security/2014/07/08/13 > > Our understanding is that Varnish Cache trusts the backend HTTP > servers for two specific properties: > > 1. integrity of the web content > 2. availability of the externally offered web service > > In the July 2014 discussion, the scenario was that a single use of a > rogue backend server, caused by DNS spoofing, could cause a long-lived > denial of service of the externally offered web service. There wasn't > a CVE ID assignment because (as a rough summary) the product resolves > DNS names only once, and the administrator is able to verify the IP > addresses before those addresses are used. > > More generally, no privilege boundary is crossed if a backend HTTP > server arbitrarily interferes with the intended behavior of the > externally offered web service. > > There's a separate question of whether a privilege boundary is crossed > if a backend HTTP server can take control of the Varnish Cache server > machine. As far as we know, the Varnish Cache vendor has not directly > commented on that. > > So, we expect that the outcome would be: > > - if the AddressSanitizer report corresponds to a buffer overflow or > buffer over-read that we understand is exploitable only for a > crash, then there won't be a CVE > > - if the AddressSanitizer report corresponds to a remote code > execution vulnerability, then it's up to the vendor to clarify > their perspective on trusting backend HTTP servers. If a system > administrator decides to use a DNS domain name in a backend > definition, and this results in reaching a wrong backend server, > and that backend server launches a successful code-execution > attack, this is perhaps sufficiently outside the bounds of > expected or reasonable behavior that a CVE is required. > > - -- > CVE assignment team, MITRE CVE Numbering Authority > M/S M300 > 202 Burlington Road, Bedford, MA 01730 USA > [ PGP key available through http://cve.mitre.org/cve/request_id.html ] > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.4.14 (SunOS) > > iQEcBAEBAgAGBQJU/zWoAAoJEKllVAevmvmsEAIIAJXn5WTb28VWOJTx2rQTUNyf > rOAsm0IzgUYYDf0+061CwTzyZrNV3IjLYBs6P2/t+Qvh1Z9F2+sDcf1cWn7dJORo > 6cc7m6hUBBaFBbYItDKp4UvnBMiyEKeC3bMEnMPdB6Z/Ukev2tO8Go6RwJL0jnDP > Ry48HSNhiJMtBmMf+PXsq4rOFz3VSvJhL0iv105URg/h8hBM0WZqhjfVL0MGuGDu > jdvlz3GR3xl7rPgaPDsKN/jdVcDVkKKvsbjD6yeJ6G28WuSg29VRDVQZX+utm5LE > MwNZzEyTqffDtSJzx1nieTczLK7wcg+bD8wmb6rwFYf/Tsy0OZGOdyf6vaJsTPU= > =tBwy > -----END PGP SIGNATURE-----
Powered by blists - more mailing lists
Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.