SECURITY: Avoid integer overflow on too many recipients

(cherry picked from commit 323ff55e67b44e95f9d3cfaba155e385aa33c4bd)
(cherry picked from commit 3a54fcd1e303bf1cc49beca7ceac35d7448860a9)

diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog
index 89a60e7579f086a00228259bb7b0606d1b59589d..3d0e638d29cfa22c3181d147a6f3261aae1004a5 100644 (file)
--- a/doc/doc-txt/ChangeLog
+++ b/doc/doc-txt/ChangeLog
@@ -280,6 +280,11 @@ PP/07 Refuse to allocate too little memory, block negative/zero allocations.
 
 PP/08 Change default for recipients_max from unlimited to 50,000.
 
+PP/09 Fix security issue with too many recipients on a message (to remove a
+      known security problem if someone does set recipients_max to unlimited,
+      or if local additions add to the recipient list).
+      Fixes CVE-2020-RCPTL reported by Qualys.
+
 
 Exim version 4.94
 -----------------

diff --git a/src/src/receive.c b/src/src/receive.c
index b0dacbd681cdba1c9e39a2589870ad38156ce594..67971c3e4ce3dded587ce5af3efd66844d2a7852 100644 (file)
--- a/src/src/receive.c
+++ b/src/src/receive.c
@@ -486,11 +486,18 @@ Returns:      nothing
 void
 receive_add_recipient(uschar *recipient, int pno)
 {
+/* XXX This is a math limit; we should consider a performance/sanity limit too. */
+const int safe_recipients_limit = INT_MAX / sizeof(recipient_item) - 1;
+
 if (recipients_count >= recipients_list_max)
   {
   recipient_item *oldlist = recipients_list;
   int oldmax = recipients_list_max;
   recipients_list_max = recipients_list_max ? 2*recipients_list_max : 50;
+  if ((recipients_list_max >= safe_recipients_limit) || (recipients_list_max < 0))
+    {
+    log_write(0, LOG_MAIN|LOG_PANIC, "Too many recipients needed: %d not satisfiable", recipients_list_max);
+    }
   recipients_list = store_get(recipients_list_max * sizeof(recipient_item), FALSE);
   if (oldlist)
     memcpy(recipients_list, oldlist, oldmax * sizeof(recipient_item));