On 2016-10-18 18:32, John Wright wrote:
Hi,
I have a constant problem with Host header forgery detection on squid
doing peek and splice.
I see this most commonly with CDN, Amazon and microsoft due to the
fact there TTL is only 5 seconds on certain dns entries im connecting
to. So when my client connects through my squid i get host header
issues due to the contstant dns changes at these destinations.
I have ready many things online but how do i get around this. I
basically want to allow certain domains or ip subnets to not hit the
host header error (as things break at this point for me ).
Any ideas ?
One example is
sls.update.microsoft.com [1]
Yes my client and Squid use same DNS server, i have even setup my
squid as a bind server and tried that just for fun same issue. Fact
is the DNS at these places changes so fast (5 seconds) the dns
response keeps changing/
I just need these approved destinations to make it through
Links:
------
[1] http://sls.update.microsoft.com/
Hi,
Are you sure, that Squid and all your clients use same _caching_ DNS
server? For example, here results from my server for name
sls.update.microsoft.com:
$ dig sls.update.microsoft.com
...
sls.update.microsoft.com.
3345 IN CNAME sls.update.microsoft.com.nsatc.net.
sls.update.microsoft.com.nsatc.net. 215 IN A 157.56.77.141
...
Second request after 3 seconds:
$ dig sls.update.microsoft.com
...
sls.update.microsoft.com.
3342 IN CNAME sls.update.microsoft.com.nsatc.net.
sls.update.microsoft.com.nsatc.net. 212 IN A 157.56.77.141
...
Here I see that the TTL for the target A record is 300 seconds (not 5
seconds), and _caching_ DNS server will serve same A record for all
clients at least 5 minutes. That behaviour will not introduce false
positives for host forgery detection.
On other hand, if the DNS server is not _caching_, you would get
different A records for each request. For example, below are results
from authoritative DNS server for zone nsatc.net:
$ dig @e.ns.nsatc.net sls.update.microsoft.com.nsatc.net
...
sls.update.microsoft.com.nsatc.net. 300 IN A 157.55.240.220
...
Second request after 5 seconds:
$ dig @e.ns.nsatc.net sls.update.microsoft.com.nsatc.net
...
sls.update.microsoft.com.nsatc.net. 300 IN A 157.56.96.54
...
Here I see, that the DNS server serves exactly one A record in
round-robin fashion. Same true for Google public DNS services. That
behavior could cause troubles for host forgery detection.
HTH
Garri
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