Always fall back to reverse DNS if trusted #844
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Whenever we have enabled trust DNS, we should fall back to using reverse DNS in all cases, not just when an IP address is given. This provides backward compatibility with the case where the client uses a DNS alias directly but the server is missing the SAN for that DNS alias (instead the server only has the canonical name for the IP address in the DN).
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Well, the answer is yes but the unfortunate problem is we don't have a good way to get around it in an expeditious way. Fortunately, where this is needed for x509 based XRootD TPC is for source selection and that is inherently much less dangerous since if there is any kind of spoofing the checksum should catch it in the end. It also helps that XRootD TPC only allows pull requests which minimizes (though does not eliminate) the severity of the exposure. |
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Whenever reverse DNS is trusted, this enables the "historical" configuration where the IP address of the connected socket is considered for reverse resolution (and the remote server's DN is compared against the resulting hostname).
IMHO, this is significantly more dangerous than "traditional' reliance on reverse DNS for non-Xrootd cases. Any attacker that is performing a MITM is able to force the client to accept any valid host certificate.
So, if the attacker controlling DNS could force
foo.example.comto resolve to attacker-controlled IP address1.2.3.4with reverse resolution ofbadguy.io, the client would accept the connection as long asbadguy.iohas a certificate from a valid authority.Fix #841