[Bug network/13935] New: getaddrinfo NXDOMAIN hijack exploit for hosts with two-component hostnames

[nagle at sitetruth dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=13935

             Bug #: 13935
           Summary: getaddrinfo NXDOMAIN hijack exploit for hosts with
                    two-component hostnames
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: network
        AssignedTo: unassigned@sourceware.org
        ReportedBy: nagle@sitetruth.com
    Classification: Unclassified


The default behavior of getaddrinfo results in a way to hijack failed
(NXDOMAIN) domain lookups. 

The man page for resolv.conf(5) says:


domain Local domain name.

Most queries for names within this domain can use short names relative to the
local domain. If no domain entry is present, the domain is determined from the
local hostname returned by gethostname(2); the domain part is taken to be
everything after the first '.'. Finally, if the hostname does not contain a
domain part, the root domain is assumed. 


Therein lies the problem.  The default case is exploitable.  If a server has a
domain name "companyname.com", the domain part, "everything after the first
'.'", is "com".  So failed a failed lookup of "xyz.com" is retried as
"xyz.com.com".  

The proprietors of "com.com" have chosen to exploit this by using a wildcard
DNS A record for "*.com.com", and redirecting the traffic thus captured to
(inevitably) an ad-heavy site.  Visit "gnu.com.com", for example.  

This problem is most visible when the hostname has two components, and the TLD
is ".com".  Most hosting services use long generated host names, such as
"gator123.hostgator.com", and so their default base domain is "hostgator.com". 
This is less exploitable.  There are "net.net" and "org.org" domains, but they
are not currently capturing undefined subdomains.  There may be other exploits
in the country

I suggest that the default behavior be changed.  Consider defaulting "ndots" to
0, or at least don't use the default domain for searches unless it has more
than a TLD.  

First reported in December 2011 at

http://serverfault.com/questions/341383/possible-nxdomain-hijacking

by a user who was puzzled that his two seemingly identical test and production
servers behaved differently.  For me, it's caused a web crawler to misidentify
nonexistent domains.

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