diff --git a/ext/openssl/tests/tls_psk_oversized_identity.phpt b/ext/openssl/tests/tls_psk_oversized_identity.phpt
new file mode 100644
index 000000000000..48b7680fd4f2
--- /dev/null
+++ b/ext/openssl/tests/tls_psk_oversized_identity.phpt
@@ -0,0 +1,55 @@
+--TEST--
+TLS PSK - oversized identity from an unserialized Psk is rejected
+--EXTENSIONS--
+openssl
+--SKIPIF--
+<?php
+if (!function_exists("proc_open")) die("skip no proc_open");
+if (OPENSSL_VERSION_NUMBER < 0x10101000) die("skip OpenSSL >= 1.1.1 required");
+?>
+--FILE--
+<?php
+$serverCode = <<<'CODE'
+    $serverCtx = stream_context_create(['ssl' => [
+        'crypto_method' => STREAM_CRYPTO_METHOD_TLSv1_2_SERVER,
+        'ciphers' => 'PSK',
+        'psk_server_cb' => function ($stream, string $identity): ?Openssl\Psk {
+            return new Openssl\Psk(str_repeat("\x42", 16));
+        },
+    ]]);
+    $server = stream_socket_server('tls://127.0.0.1:0', $errno, $errstr,
+        STREAM_SERVER_BIND | STREAM_SERVER_LISTEN, $serverCtx);
+    phpt_notify_server_start($server);
+    @stream_socket_accept($server, 3);
+CODE;
+
+$clientCode = <<<'CODE'
+    // unserialize bypasses the constructor length check, so the Psk carries a
+    // 512-byte identity; the callback must reject it, not overflow the buffer.
+    $identity = str_repeat('A', 512);
+    $payload = sprintf('O:11:"Openssl\Psk":2:{s:3:"psk";s:4:"pass";s:8:"identity";s:%d:"%s";}',
+        strlen($identity), $identity);
+
+    $clientCtx = stream_context_create(['ssl' => [
+        'crypto_method' => STREAM_CRYPTO_METHOD_TLSv1_2_CLIENT,
+        'ciphers' => 'PSK',
+        'verify_peer' => false,
+        'verify_peer_name' => false,
+        'psk_client_cb' => function ($stream) use ($payload): ?Openssl\Psk {
+            return unserialize($payload);
+        },
+    ]]);
+    try {
+        @stream_socket_client('tls://{{ ADDR }}', $errno, $errstr,
+            30, STREAM_CLIENT_CONNECT, $clientCtx);
+        echo "no exception\n";
+    } catch (ValueError $e) {
+        echo "caught: ", $e->getMessage(), "\n";
+    }
+CODE;
+
+include __DIR__ . '/ServerClientTestCase.inc';
+ServerClientTestCase::getInstance()->run($clientCode, $serverCode);
+?>
+--EXPECTF--
+caught: PSK identity must be shorter than %d bytes
diff --git a/ext/openssl/xp_ssl.c b/ext/openssl/xp_ssl.c
index 5cead037715a..b8f330f91f8a 100644
--- a/ext/openssl/xp_ssl.c
+++ b/ext/openssl/xp_ssl.c
@@ -1772,8 +1772,6 @@ static unsigned int php_openssl_psk_client_cb(SSL *ssl, const char *hint,
 		unsigned char *psk_out, unsigned int max_psk_len)
 {
 	(void)hint; /* identity hint deliberately not exposed as it is useless */
-	(void)max_identity_len;
-	(void)max_psk_len;
 
 	php_stream *stream = (php_stream *)SSL_get_ex_data(ssl,
 			php_openssl_get_ssl_stream_data_index());
@@ -1812,6 +1810,18 @@ static unsigned int php_openssl_psk_client_cb(SSL *ssl, const char *hint,
 		return 0;
 	}
 
+	/* Returned lengths are untrusted, so bound them to the buffers. */
+	if (ZSTR_LEN(identity_str) >= max_identity_len) {
+		zend_value_error("PSK identity must be shorter than %u bytes", max_identity_len);
+		zval_ptr_dtor(&result);
+		return 0;
+	}
+	if (ZSTR_LEN(psk_str) > max_psk_len) {
+		zend_value_error("PSK key must not exceed %u bytes", max_psk_len);
+		zval_ptr_dtor(&result);
+		return 0;
+	}
+
 	memcpy(identity_out, ZSTR_VAL(identity_str), ZSTR_LEN(identity_str));
 	identity_out[ZSTR_LEN(identity_str)] = '\0';
 	memcpy(psk_out, ZSTR_VAL(psk_str), ZSTR_LEN(psk_str));
@@ -1824,8 +1834,6 @@ static unsigned int php_openssl_psk_client_cb(SSL *ssl, const char *hint,
 static unsigned int php_openssl_psk_server_cb(SSL *ssl, const char *identity,
 		unsigned char *psk_out, unsigned int max_psk_len)
 {
-	(void)max_psk_len;
-
 	php_stream *stream = (php_stream *)SSL_get_ex_data(ssl,
 			php_openssl_get_ssl_stream_data_index());
 	if (stream == NULL) {
@@ -1865,6 +1873,13 @@ static unsigned int php_openssl_psk_server_cb(SSL *ssl, const char *identity,
 		return 0;
 	}
 
+	/* Returned length is untrusted, so bound it to the buffer. */
+	if (ZSTR_LEN(psk_str) > max_psk_len) {
+		zend_value_error("PSK key must not exceed %u bytes", max_psk_len);
+		zval_ptr_dtor(&result);
+		return 0;
+	}
+
 	memcpy(psk_out, ZSTR_VAL(psk_str), ZSTR_LEN(psk_str));
 	unsigned int psk_len = (unsigned int)ZSTR_LEN(psk_str);
 
@@ -1930,6 +1945,14 @@ static int php_openssl_psk_use_session_cb(SSL *ssl, const EVP_MD *md,
 		return 0;
 	}
 
+	/* Returned length is untrusted, so bound it to the buffer. */
+	if (ZSTR_LEN(identity_str) > PHP_OPENSSL_PSK_MAX_IDENTITY_LEN) {
+		zend_value_error("PSK identity must not exceed %d bytes", PHP_OPENSSL_PSK_MAX_IDENTITY_LEN);
+		SSL_SESSION_free(session);
+		zval_ptr_dtor(&result);
+		return 0;
+	}
+
 	/* Identity buffer must outlive this callback. */
 	if (sslsock->psk_identity_buf == NULL) {
 		sslsock->psk_identity_buf = emalloc(PHP_OPENSSL_PSK_MAX_IDENTITY_LEN);