diff --git a/src/wh_client_crypto.c b/src/wh_client_crypto.c
index 89b5a3649..02c031cdc 100644
--- a/src/wh_client_crypto.c
+++ b/src/wh_client_crypto.c
@@ -2826,14 +2826,30 @@ int wh_Client_Curve25519SharedSecret(whClientContext* ctx,
                     /* wolfCrypt allows positive error codes on success in some
                      * scenarios */
                     if (ret >= 0) {
+                        uint8_t*     res_out = (uint8_t*)(res + 1);
+                        const size_t hdr_sz =
+                            sizeof(whMessageCrypto_GenericResponseHeader) +
+                            sizeof(*res);
+                        /* Defensive bound: res->sz must fit within the actual
+                         * received frame */
+                        if (res_len < hdr_sz || res->sz > (res_len - hdr_sz)) {
+                            ret = WH_ERROR_ABORTED;
+                        }
                         if (out_size != NULL) {
+                            if ((ret >= 0) && 
+                                (out != NULL) && (res->sz > *out_size)) {
+                                /* Output buffer too small. Report required size
+                                * and fail rather than silently truncating
+                                * X25519 key material. */
+                                ret = WH_ERROR_BUFFER_SIZE;
+                            }
+                            /* Give caller the required size, even on failure */
                             *out_size = res->sz;
-                        }
-                        if (out != NULL) {
-                            uint8_t* res_out = (uint8_t*)(res + 1);
-                            memcpy(out, res_out, res->sz);
-                            WH_DEBUG_VERBOSE_HEXDUMP("[client] X25519:", res_out,
-                                             res->sz);
+                            if ((ret >= 0) && (out != NULL) && (res->sz > 0)) {
+                                memcpy(out, res_out, res->sz);
+                                WH_DEBUG_VERBOSE_HEXDUMP("[client] X25519:",
+                                                         res_out, res->sz);
+                            }
                         }
                     }
                 }