diff --git a/ChangeLog.d/xxx_psa_peerkey.txt b/ChangeLog.d/xxx_psa_peerkey.txt
new file mode 100644
index 000000000..d25e4ecbf
--- /dev/null
+++ b/ChangeLog.d/xxx_psa_peerkey.txt
@@ -0,0 +1,8 @@
+Security
+   * Fix a remotely exploitable heap buffer overflow in TLS handshake parsing.
+     In TLS 1.3, all configurations are affected except PSK-only ones, and
+     both clients and servers are affected.
+     In TLS 1.2, the affected configurations are those with
+     MBEDTLS_USE_PSA_CRYPTO and ECDH enabled but DHM and RSA disabled,
+     and only servers are affected, not clients.
+     Credit to OSS-Fuzz.
diff --git a/library/ssl_tls12_client.c b/library/ssl_tls12_client.c
index cc22a3fe1..27bbafa06 100644
--- a/library/ssl_tls12_client.c
+++ b/library/ssl_tls12_client.c
@@ -1727,7 +1727,7 @@ static int ssl_parse_server_ecdh_params(mbedtls_ssl_context *ssl,
                                         unsigned char *end)
 {
     uint16_t tls_id;
-    uint8_t ecpoint_len;
+    size_t ecpoint_len;
     mbedtls_ssl_handshake_params *handshake = ssl->handshake;
     psa_key_type_t key_type = PSA_KEY_TYPE_NONE;
     size_t ec_bits = 0;
@@ -1779,7 +1779,7 @@ static int ssl_parse_server_ecdh_params(mbedtls_ssl_context *ssl,
         return MBEDTLS_ERR_SSL_DECODE_ERROR;
     }
 
-    if (ecpoint_len > PSA_KEY_EXPORT_ECC_PUBLIC_KEY_MAX_SIZE(PSA_VENDOR_ECC_MAX_CURVE_BITS)) {
+    if (ecpoint_len > sizeof(handshake->xxdh_psa_peerkey)) {
         return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
     }
 
@@ -2059,7 +2059,7 @@ static int ssl_get_ecdh_params_from_cert(mbedtls_ssl_context *ssl)
     ret = mbedtls_ecp_point_write_binary(&peer_key->grp, &peer_key->Q,
                                          MBEDTLS_ECP_PF_UNCOMPRESSED, &olen,
                                          ssl->handshake->xxdh_psa_peerkey,
-                                         MBEDTLS_PSA_MAX_EC_PUBKEY_LENGTH);
+                                         sizeof(ssl->handshake->xxdh_psa_peerkey));
 
     if (ret != 0) {
         MBEDTLS_SSL_DEBUG_RET(1, ("mbedtls_ecp_point_write_binary"), ret);
diff --git a/library/ssl_tls12_server.c b/library/ssl_tls12_server.c
index d2143ac15..6ebd5064f 100644
--- a/library/ssl_tls12_server.c
+++ b/library/ssl_tls12_server.c
@@ -3718,22 +3718,32 @@ static int ssl_parse_client_key_exchange(mbedtls_ssl_context *ssl)
         psa_status_t status = PSA_ERROR_GENERIC_ERROR;
         mbedtls_ssl_handshake_params *handshake = ssl->handshake;
 
-        MBEDTLS_SSL_DEBUG_MSG(1, ("Read the peer's public key."));
+        MBEDTLS_SSL_DEBUG_MSG(3, ("Read the peer's public key."));
 
         /*
          * We must have at least two bytes (1 for length, at least 1 for data)
          */
         if (buf_len < 2) {
-            MBEDTLS_SSL_DEBUG_MSG(1, ("Invalid buffer length"));
-            return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
+            MBEDTLS_SSL_DEBUG_MSG(1, ("Invalid buffer length: %" MBEDTLS_PRINTF_SIZET,
+                                      buf_len));
+            return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
         }
 
         if (data_len < 1 || data_len > buf_len) {
-            MBEDTLS_SSL_DEBUG_MSG(1, ("Invalid data length"));
-            return MBEDTLS_ERR_ECP_BAD_INPUT_DATA;
+            MBEDTLS_SSL_DEBUG_MSG(1, ("Invalid data length: %" MBEDTLS_PRINTF_SIZET
+                                      " > %" MBEDTLS_PRINTF_SIZET,
+                                      data_len, buf_len));
+            return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
         }
 
         /* Store peer's ECDH public key. */
+        if (data_len > sizeof(handshake->xxdh_psa_peerkey)) {
+            MBEDTLS_SSL_DEBUG_MSG(1, ("Invalid public key length: %" MBEDTLS_PRINTF_SIZET
+                                      " > %" MBEDTLS_PRINTF_SIZET,
+                                      data_len,
+                                      sizeof(handshake->xxdh_psa_peerkey)));
+            return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
+        }
         memcpy(handshake->xxdh_psa_peerkey, p, data_len);
         handshake->xxdh_psa_peerkey_len = data_len;
 
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 81fa514f6..7072677f1 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -1516,7 +1516,13 @@ int mbedtls_ssl_tls13_read_public_xxdhe_share(mbedtls_ssl_context *ssl,
     /* Check if key size is consistent with given buffer length. */
     MBEDTLS_SSL_CHK_BUF_READ_PTR(p, end, peerkey_len);
 
-    /* Store peer's ECDH public key. */
+    /* Store peer's ECDH/FFDH public key. */
+    if (peerkey_len > sizeof(handshake->xxdh_psa_peerkey)) {
+        MBEDTLS_SSL_DEBUG_MSG(1, ("Invalid public key length: %u > %" MBEDTLS_PRINTF_SIZET,
+                                  (unsigned) peerkey_len,
+                                  sizeof(handshake->xxdh_psa_peerkey)));
+        return MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE;
+    }
     memcpy(handshake->xxdh_psa_peerkey, p, peerkey_len);
     handshake->xxdh_psa_peerkey_len = peerkey_len;