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http://www.exim.org/bugzilla/show_bug.cgi?id=512

           Summary: [PATCH] Let client authentication depend upon TLS being
                    present
           Product: Exim
           Version: N/A
          Platform: Other
        OS/Version: All
            Status: NEW
          Keywords: work:tiny
          Severity: wishlist
          Priority: medium
         Component: SMTP Authentication
        AssignedTo: [EMAIL PROTECTED]
        ReportedBy: [EMAIL PROTECTED]
         QAContact: [email protected]


A man-in-the-middle attack could strip STARTTLS from the EHLO response codes. 
If a cleartext authentication protocol is configured then this can leak
authentication credentials so that they can be sniffed.

I'll attach a patch which:
 * adds "client_attempt_condition" as an analogue to
"server_advertise_condition"
 * adds a new variable "connection_tls_cipher", only set during the smtp
transport
 * does not include documentations because
   * I suck
   * I may have done this badly

My recollection is that a process performing outbound SMTP won't be re-used so
it's safe to "set and forget" a global variable in the way that this patch
does.  This is what I've probably gotten wrong ...

Testing consisted of:
 1: client_attempt_condition = ${if def:connection_tls_cipher}
 2: send mail via GMail Submission (PLAIN)
 3: client_attempt_condition = no
 4: send another mail, see it blocked in queue; run "exim -d -qff" and verify
that no matching authenticator is found
 5: restore client_attempt_condition
 6: watch mail get sent out

Feedback welcome.  Variable renames fully expected.

-Phil Pennock

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