libssl: fix API misuse in legacy finished handling

This looks like a potential out of bounds read or allowing trailing garbage
in peer_finished. It's harmless because CBS_len() is compared against the
s->s3->hs.peer_finished_len a few lines up, thus it is only cosmetic.

discussed with jsing
ok kenjiro

2 files changed, 6 insertions, 4 deletions

diff --git a/src/lib/libssl/ssl_clnt.c b/src/lib/libssl/ssl_clnt.c
index 69221332f5..37684aba91 100644
--- a/src/lib/libssl/ssl_clnt.c
+++ b/src/lib/libssl/ssl_clnt.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_clnt.c,v 1.176 2026/08/21 17:15:22 tb Exp $ */
+/* $OpenBSD: ssl_clnt.c,v 1.177 2026/08/29 08:41:17 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -2348,7 +2348,8 @@ ssl3_get_server_finished(SSL *s)
                 goto fatal_err;
         }
 
-        if (!CBS_mem_equal(&cbs, s->s3->hs.peer_finished, CBS_len(&cbs))) {
+        if (!CBS_mem_equal(&cbs,
+            s->s3->hs.peer_finished, s->s3->hs.peer_finished_len)) {
                 al = SSL_AD_DECRYPT_ERROR;
                 SSLerror(s, SSL_R_DIGEST_CHECK_FAILED);
                 goto fatal_err;
diff --git a/src/lib/libssl/ssl_srvr.c b/src/lib/libssl/ssl_srvr.c
index 43260d8065..a12f552bea 100644
--- a/src/lib/libssl/ssl_srvr.c
+++ b/src/lib/libssl/ssl_srvr.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_srvr.c,v 1.171 2026/08/21 17:15:22 tb Exp $ */
+/* $OpenBSD: ssl_srvr.c,v 1.172 2026/08/29 08:41:17 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -2373,7 +2373,8 @@ ssl3_get_client_finished(SSL *s)
                 goto fatal_err;
         }
 
-        if (!CBS_mem_equal(&cbs, s->s3->hs.peer_finished, CBS_len(&cbs))) {
+        if (!CBS_mem_equal(&cbs,
+            s->s3->hs.peer_finished, s->s3->hs.peer_finished_len)) {
                 al = SSL_AD_DECRYPT_ERROR;
                 SSLerror(s, SSL_R_DIGEST_CHECK_FAILED);
                 goto fatal_err;