Fix base64d() buffer size (CVE-2018-6789)

Credits for discovering this bug: Meh Chang <meh@devco.re>

(cherry picked from commit 062990cc1b2f9e5d82a413b53c8f0569075de700)

diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog
index 1ee00168f93ca4a0f74c4523071956becf8700fa..8ae418ab1f7cc2ab8f04a5471eea225c272248db 100644 (file)
--- a/doc/doc-txt/ChangeLog
+++ b/doc/doc-txt/ChangeLog
@@ -5,8 +5,8 @@ affect Exim's operation, with an unchanged configuration file.  For new
 options, and new features, see the NewStuff file next to this ChangeLog.
 
 
-Exim version 4.91
------------------
+Since Exim version 4.90
+-----------------------
 
 JH/01 Replace the store_release() internal interface with store_newblock(),
       which internalises the check required to safely use the old one, plus
@@ -82,6 +82,8 @@ JH/15 Relax results from ACL control request to enable cutthrough, in
       ignoring.  This covers use with PRDR, frozen messages, queue-only and
       fake-reject.
 
+HS/01 Fix Buffer overflow in base64d() (CVE-2018-6789)
+
 JH/16 Fix bug in DKIM verify: a buffer overflow could corrupt the malloc
       metadata, resulting in a crash in free().
 

diff --git a/src/src/base64.c b/src/src/base64.c
index ae6874b8a8b255335116fd81ef4746d5c40ffdbe..1d84c1e5c34116bbfdf9b137bd26ba19b1f3a1da 100644 (file)
--- a/src/src/base64.c
+++ b/src/src/base64.c
@@ -152,10 +152,14 @@ static uschar dec64table[] = {
 int
 b64decode(const uschar *code, uschar **ptr)
 {
+
 int x, y;
-uschar *result = store_get(3*(Ustrlen(code)/4) + 1);
+uschar *result;
 
-*ptr = result;
+{
+  int l = Ustrlen(code);
+  *ptr = result = store_get(1 + l/4 * 3 + l%4);
+}
 
 /* Each cycle of the loop handles a quantum of 4 input bytes. For the last
 quantum this may decode to 1, 2, or 3 output bytes. */