Patch from upstream:
http://vcs.pcre.org/pcre?view=revision&revision=1566
to fix CVE-2015-3217 for this upstream bug
https://bugs.exim.org/show_bug.cgi?id=1638

This patch may be removed when pcre is upgraded from version 8.37

--- pcre-8.37-orig/ChangeLog	2015-06-18 14:42:05.162869794 -0700
+++ pcre-8.37/ChangeLog	2015-06-18 14:42:49.750142570 -0700
@@ -23,6 +23,10 @@ Changes since Version 8.37
     another group caused a buffer overflow. For example:
     /(?J)(?'d'(?'d'\g{d}))/. This bug was discovered by the LLVM fuzzer.
  
+5.  If a non-capturing group containing a conditional group that could match
+    an empty string was repeated, it was not identified as matching an empty
+    string itself. For example: /^(?:(?(1)x|)+)+$()/.
+
 
 Version 8.37 28-April-2015
 --------------------------
--- pcre-8.37-orig/pcre_compile.c	2015-06-18 14:43:18.613383953 -0700
+++ pcre-8.37/pcre_compile.c	2015-06-18 14:44:14.866515479 -0700
@@ -2487,7 +2487,7 @@ for (code = first_significant_code(code 
   if (c == OP_BRA  || c == OP_BRAPOS ||
       c == OP_CBRA || c == OP_CBRAPOS ||
       c == OP_ONCE || c == OP_ONCE_NC ||
-      c == OP_COND)
+      c == OP_COND || c == OP_SCOND)
     {
     BOOL empty_branch;
     if (GET(code, 1) == 0) return TRUE;    /* Hit unclosed bracket */
--- pcre-8.37-orig/testdata/testinput2	2015-06-18 14:45:30.453719449 -0700
+++ pcre-8.37/testdata/testinput2	2015-06-18 14:46:14.175672070 -0700
@@ -4168,4 +4168,6 @@ backtracking verbs. --/
 
 "(?J)(?'d'(?'d'\g{d}))"
 
+/^(?:(?(1)x|)+)+$()/BZ
+
 /-- End of testinput2 --/
--- pcre-8.37-orig/testdata/testoutput2	2015-06-18 14:45:38.047882931 -0700
+++ pcre-8.37/testdata/testoutput2	2015-06-18 14:47:02.815368178 -0700
@@ -14456,4 +14456,22 @@ Failed: reference to non-existent subpat
 
 "(?J)(?'d'(?'d'\g{d}))"
 
+/^(?:(?(1)x|)+)+$()/BZ
+------------------------------------------------------------------
+        Bra
+        ^
+        SBra
+        SCond
+      1 Cond ref
+        x
+        Alt
+        KetRmax
+        KetRmax
+        $
+        CBra 1
+        Ket
+        Ket
+        End
+------------------------------------------------------------------
+
 /-- End of testinput2 --/