Fixed by #39751 by KevinJohnHoffman at gmail dot com

ext/standard/basic_functions.c

@@ -3837,6 +3837,9 @@ static void php_putenv_destructor(putenv_entry *pe)
 		SetEnvironmentVariable(pe->key, "bugbug");
 #endif
 		putenv(pe->previous_value);
+# if defined(PHP_WIN32)
+		efree(pe->previous_value);
+# endif
 	} else {
 # if HAVE_UNSETENV
 		unsetenv(pe->key);
@@ -4430,7 +4433,12 @@ PHP_FUNCTION(putenv)
 		pe.previous_value = NULL;
 		for (env = environ; env != NULL && *env != NULL; env++) {
 			if (!strncmp(*env, pe.key, pe.key_len) && (*env)[pe.key_len] == '=') {	/* found it */
+#if defined(PHP_WIN32)
+				/* must copy previous value because MSVCRT's putenv can free the string without notice */
+				pe.previous_value = estrndup(*env, 1024);
+#else
 				pe.previous_value = *env;
+#endif
 				break;
 			}
 		}