virtualenv is a tool for creating isolated virtual python environments. From 20.26.6 until 21.14.2, ViaTemplateActivator.instantiate template() replaces placeholders one key at a time across the complete activation template, so trigger names such as VIRTUAL NAME , VIRTUAL ENV , or VIRTUAL PROMPT inside an already substituted and quoted environment path or prompt can be replaced during a later pass. The later value's quoting can close the earlier literal and execute the remaining path when a user activates the environment through bash, fish, xonsh, or activate this.py. The distinct csh prompt-display token VIRTUAL PROMPT DISPLAY TCSH can instead break the generated script without establishing command execution. The attacker must influence the destination path or --prompt, and a value without a relevant placeholder name does not trigger this mechanism. This issue is fixed in version 21.14.2.