pamusb provides hardware authentication for Linux using ordinary removable media. Prior to 0.8.7, pamusb-pinentry reads the PINENTRYFALLBACKAPP environment variable and executes it directly without any validation. Any process that can set environment variables before pamusb-pinentry is invoked can point PINENTRYFALLBACKAPP at an arbitrary binary or script and have it executed with the privileges of the pamusb tool chain. This vulnerability is fixed in 0.8.7.