If the SMTP session was over IPv6, what should the "remote-ip" environment
item be set to?
I would think that in this case it would obviously be the IPv6 address.
However, I take your point that the format of such addresses needs to be
specified - the underlying standards for address formats having failed to
specify this with sufficient clarity or generality, it is now up to every
application protocol where such addresses appear to deal with it separately.
Sigh. Not the way it should be, but how it is.
Perhaps there should be a prefix on the value that
indicates the address family, or it should be formatted like the 'host'
part of URI?
Note that the obvious test of
environment :matches "remote-ip" "*.*.*.*"
will match an IPv6 address literal if the implementation uses the
x:x:x:x:x:x:d.d.d.d
form, such as with the IPv4 compat addresses, ala "::FFFF:1.2.3.4".
(Yes, this thought was triggered by the "IPv6-only" experiment during the
IETF technical plenary.)
Well, I certainly hope that for any given address there's exactly one way it
will end up being represented. If that's not the case then there's a major
problem that goes far beyond this specific issue.
There's also the issue of how any future sort of address should be handled.
Since RFC 2821 has already had to deal with this I think the best way to handle
it is by referring to the formats defined there. I currently have:
"remote-ip"
=> IP address of remote SMTP/LMTP/Submission client, if
applicable and available. IPv4, IPv6, and other types of
addresses are respectively represented in the formats
defined by the IPv4-address-literal, IPv6-address-literal,
and General-address-literal productions defined in
[RFC 2821] section 4.1.3.
There probably should be a security consideration that explains that the
value of the "remote-host" item may be controlled by an untrusted source.
For example, the test
environment :matches "remote-host" "*.mydomain.com"
is *not* a good way to test whether the message came from 'outside' unless
the implementation there's some sort of IP->host->IP consistency check
made.
Also a good point. I have added:
The remote-host environment item defined in this specification is usually
determined by performing a PTR DNS lookup on the client IP address. This
information may come from an untrusted source. For example, the test:
if environment :matches "remote-host" "*.mydomain.com" { ... }
is not a good way to test whether the message came from 'outside' becaus
anyone who can create a PTR record can create one that refers to whatever
domain they choose.
(The sendmail MTA faced the above issues some time ago for the pre-defined
variables it provides to its rulesets. To quote the sendmail operations
guide, it defined variables as follows:
${client_addr}
The IP address of the SMTP client. IPv6
addresses are tagged with "IPv6:" before the
address. Defined in the SMTP server only.
${client_name}
The host name of the SMTP client. This may be
the client's bracketed IP address in the form [
nnn.nnn.nnn.nnn ] for IPv4 and [
IPv6:nnnn:...:nnnn ] for IPv6 if the client's IP
address is not resolvable, or if it is resolvable
but the IP address of the resolved hostname
doesn't match the original IP address. Defined
in the SMTP server only. See also
${client_resolve}.
I think a simpler way to handle this is to say that the name will
be blank if it cannot be resolved into a host name. How about:
"remote-host"
=> Host name of remote SMTP/LMTP/Submission client, if
applicable and available. The empty string will be returned
if for some reason this information cannot be obtained for
the current client.
${client_ptr}
The result of the PTR lookup for the client IP
address. Note: this is the same as
${client_name} if and only if ${client_resolve}
is OK. Defined in the SMTP server only.
${client_resolve}
Holds the result of the resolve call for
${client_name}. Possible values are:
OK resolved successfully
FAIL permanent lookup failure
FORGED forward lookup doesn't match reverse lookup
TEMP temporary lookup failure
Defined in the SMTP server only. sendmail
performs a hostname lookup on the IP address of
the connecting client. Next the IP addresses of
that hostname are looked up. If the client IP
address does not appear in that list, then the
hostname is maybe forged. This is reflected as
the value FORGED for ${client_resolve} and it
also shows up in $_ as "(may be forged)".
While client_ptr and client_resolve are probably overkill for the sieve
environment extension, the tagging in client_addr and precise definition
of when client_name contains a name and not an address literal seem like
practical guidance in this area.)
I agree - see above for my proposed solution for this issue.
Ned