A vulnerability in virtualenv's xonsh activation script allows attacker-controlled prompt text to become executable code during environment activation if the xonsh source decoding uses legacy multibyte encodings like GBK or Big5. This occurs because UTF-8 encoded activation scripts containing non-ASCII characters are misinterpreted under these encodings, causing string literals to be improperly closed and arbitrary statements to execute. The issue affects POSIX activation scripts and requires an attacker to control the prompt or destination argument passed to virtualenv, with the user subsequently activating the environment. A fix is available in virtualenv version 2.29.3.