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Fix OCSP Status Request extension unbounded memory growth

A malicious client can send an excessively large OCSP Status Request
extension. If that client continually requests renegotiation,
sending a large OCSP Status Request extension each time, then there will
be unbounded memory growth on the server. This will eventually lead to a
Denial Of Service attack through memory exhaustion. Servers with a
default configuration are vulnerable even if they do not support OCSP.
Builds using the "no-ocsp" build time option are not affected.

I have also checked other extensions to see if they suffer from a similar
problem but I could not find any other issues.

CVE-2016-6304

Issue reported by Shi Lei.

Reviewed-by: Rich Salz <rsalz@openssl.org>
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1 parent a449b47 commit e408c09bbf7c3057bda4b8d20bec1b3a7771c15b @mattcaswell mattcaswell committed Sep 9, 2016
Showing with 16 additions and 7 deletions.
  1. +16 −7 ssl/t1_lib.c
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@@ -2019,6 +2019,22 @@ static int ssl_scan_clienthello_tlsext(SSL *s, PACKET *pkt, int *al)
(&extension, &responder_id_list))
return 0;
+ /*
+ * We remove any OCSP_RESPIDs from a previous handshake
+ * to prevent unbounded memory growth - CVE-2016-6304
+ */
+ sk_OCSP_RESPID_pop_free(s->tlsext_ocsp_ids,
+ OCSP_RESPID_free);
+ if (PACKET_remaining(&responder_id_list) > 0) {
+ s->tlsext_ocsp_ids = sk_OCSP_RESPID_new_null();
+ if (s->tlsext_ocsp_ids == NULL) {
+ *al = SSL_AD_INTERNAL_ERROR;
+ return 0;
+ }
+ } else {
+ s->tlsext_ocsp_ids = NULL;
+ }
+
while (PACKET_remaining(&responder_id_list) > 0) {
OCSP_RESPID *id;
PACKET responder_id;
@@ -2030,13 +2046,6 @@ static int ssl_scan_clienthello_tlsext(SSL *s, PACKET *pkt, int *al)
return 0;
}
- if (s->tlsext_ocsp_ids == NULL
- && (s->tlsext_ocsp_ids =
- sk_OCSP_RESPID_new_null()) == NULL) {
- *al = SSL_AD_INTERNAL_ERROR;
- return 0;
- }
-
id_data = PACKET_data(&responder_id);
id = d2i_OCSP_RESPID(NULL, &id_data,
PACKET_remaining(&responder_id));

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