Fix a hang with SSL_peek()

If while calling SSL_peek() we read an empty record then we go into an infinite loop, continually trying to read data from the empty record and never making any progress. This could be exploited by a malicious peer in a Denial Of Service attack. CVE-2016-6305 GitHub Issue #1563 Reviewed-by: Rich Salz <rsalz@openssl.org>
openssl · Sep 22, 2016 · 6365810 · 6365810
1 parent 6d32c2a
commit 6365810
Showing 1 changed file with 5 additions and 1 deletion.
diff --git a/ssl/record/rec_layer_s3.c b/ssl/record/rec_layer_s3.c
@@ -1133,7 +1133,11 @@ int ssl3_read_bytes(SSL *s, int type, int *recvd_type, unsigned char *buf,
 
             memcpy(buf, &(rr->data[rr->off]), n);
             buf += n;
-            if (!peek) {
+            if (peek) {
+                /* Mark any zero length record as consumed CVE-2016-6305 */
+                if (SSL3_RECORD_get_length(rr) == 0)
+                    SSL3_RECORD_set_read(rr);
+            } else {
                 SSL3_RECORD_sub_length(rr, n);
                 SSL3_RECORD_add_off(rr, n);
                 if (SSL3_RECORD_get_length(rr) == 0) {