An example exploit failed against my system, because I had this sanity guard in
place; it's not a real security fix since a careful attacker could find enough
valid recipients to hit that problem, but it highlights that this is a useful
enough pattern that we should encourage its wider use.
(cherry picked from commit
2a636a39fff29b7c3da1798767a510dfed982a62)
(cherry picked from commit
346f96bad326893f9c1fa772a5b8ac35b1f8f7bd)
HS/02 Handle SIGINT as we handle SIGTERM: terminate the Exim process.
HS/02 Handle SIGINT as we handle SIGTERM: terminate the Exim process.
+PP/01 Add a too-many-bad-recipients guard to the default config's RCPT ACL.
+
Exim version 4.94
-----------------
Exim version 4.94
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+ # Reject all RCPT commands after too many bad recipients
+ # This is partly a defense against spam abuse and partly attacker abuse.
+ # Real senders should manage, by the time they get to 10 RCPT directives,
+ # to have had at least half of them be real addresses.
+ #
+ # This is a lightweight check and can protect you against repeated
+ # invocations of more heavy-weight checks which would come after it.
+
+ deny condition = ${if and {\
+ {>{$rcpt_count}{10}}\
+ {<{$recipients_count}{${eval:$rcpt_count/2}}} }}
+ message = Rejected for too many bad recipients
+ logwrite = REJECT [$sender_host_address]: bad recipient count high [${eval:$rcpt_count-$recipients_count}]
+
# Accept if the message comes from one of the hosts for which we are an
# outgoing relay. It is assumed that such hosts are most likely to be MUAs,
# so we set control=submission to make Exim treat the message as a
# Accept if the message comes from one of the hosts for which we are an
# outgoing relay. It is assumed that such hosts are most likely to be MUAs,
# so we set control=submission to make Exim treat the message as a