From: Jeremy Harris <jgh146exb@wizmail.org>
Date: Wed, 8 Jan 2020 13:51:42 +0000 (+0000)
Subject: Docs: warn against using $local_part directly in delivery
X-Git-Url: https://git.exim.org/users/jgh/exim.git/commitdiff_plain/cf8b2c5789b6b6cfc2bb0dd84753ed7ec746d444?ds=sidebyside

Docs: warn against using $local_part directly in delivery
---

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index 4d02bdc32..8b1522795 100644
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -6362,7 +6362,7 @@ All other options are defaulted.
 .code
 local_delivery:
   driver = appendfile
-  file = /var/mail/$local_part
+  file = /var/mail/$home
   delivery_date_add
   envelope_to_add
   return_path_add
@@ -12385,6 +12385,18 @@ Global address rewriting happens when a message is received, so the value of
 because a message may have many recipients and the system filter is called just
 once.
 
+.new
+&*Warning*&: the content of this variable is provided by a potential attacker.
+Consider carefully the implications of using it unvalidated as a name
+for file access.
+This presents issues for users' &_.forward_& and filter files.
+For traditional full user accounts, use &%check_local_users%& and the &$home$&
+variable rather than this one.
+For virtual users, store a suitable pathname component in the database
+which is used for account name validation, and use that retrieved value
+rather than this variable.
+.wen
+
 .vindex "&$local_part_prefix$&"
 .vindex "&$local_part_suffix$&"
 .cindex affix variables
@@ -20528,6 +20540,15 @@ is not the case when the file contains syntactically valid items that happen to
 yield empty addresses, for example, items containing only RFC 2822 address
 comments.
 
+.new
+&*Warning*&: It is unwise to use &$local_part$& or &$domain$&
+directly for redirection,
+as they are provided by a potential attacker.
+In the examples above, &$local_part$& is used for looking up data held locally
+on the system, and not used directly (the second example derives &$home$& via
+the passsword file or database, using &$local_part$&).
+.wen
+
 
 
 .section "Forward files and address verification" "SECID125"
diff --git a/src/src/configure.default b/src/src/configure.default
index cf38305e5..08f5a9d10 100644
--- a/src/src/configure.default
+++ b/src/src/configure.default
@@ -863,7 +863,7 @@ smarthost_smtp:
 
 local_delivery:
   driver = appendfile
-  file = /var/mail/$local_part
+  file = /var/mail/$home
   delivery_date_add
   envelope_to_add
   return_path_add