A vulnerability in virtualenv's xonsh activation script allows attacker-controlled prompt text to become executable code during environment activation if the script is decoded using legacy multibyte encodings like GBK or Big5. This occurs because the UTF-8 activation script contains non-ASCII characters that, when decoded under these encodings, alter how quotes are interpreted, enabling code injection. The attack requires control of the prompt or destination argument passed to virtualenv and subsequent sourcing of the generated activation script. The issue affects POSIX activation scripts and is fixed by changing the quoting method to emit only ASCII escapes.