the affected platforms, this vulnerability allowed an attacker with access to the DCL command line to carry out a privilege escalation attack. The vulnerability relies on exploiting a buffer overflow bug in the DCL command processing code, the ability for a user to interrupt a running image (program executable) with and return to the DCL prompt, and the fact that DCL retains the privileges of the interrupted image. The buffer overflow bug allowed shellcode to be executed with the privileges of an interrupted image. This could be used in conjunction with an image installed with higher privileges than the attacker's account to bypass system security. POSIX compatibility Various official Unix and POSIX compatibility layers were created for VMS. The first of which was DEC/Shell - which was a layered product consisting of ports of the Version 7 Unix Bourne shell and several other Unix utilities to VAX/VMS. In 1992, DEC released the POSIX for OpenVMS layered product, which included a shell based on the Korn Shell. POSIX for OpenVMS was later replaced by the open source GNV (GNU's not VMS) project, which was first included in OpenVMS media in 2002. Amongst other GNU tools, GNV includes a port of the Bash shell to VMS. Examples of third party Unix compatibility layers for VMS include Eunice. Hobbyist programs In 1997 OpenVMS and a number of layered products were made available free of charge for hobbyist, non-commercial use as part of the OpenVMS Hobbyist Program. Since then, several companies producing OpenVMS software have made their products available under the same terms, such as Process Software. Prior to the x86-64 port, the age and cost of hardware capable of running OpenVMS made emulators such as SIMH a common choice for hobbyist installations. In March 2020, HPE announced the end of the OpenVMS Hobbyist Program. This was followed by VSI's announcement of the Community License Program (CLP) in April 2020, which was intended as a replacement for the HPE Hobbyist Program. The CLP was launched in July 2020, and provides licenses for VSI OpenVMS releases on Alpha and Integrity systems. OpenVMS x86-64 licenses will be made available when a stable version is released for this architecture. OpenVMS for VAX is not covered by the CLP, since there are no VSI releases of OpenVMS VAX, and the old versions are still owned by HPE. Release history See also Comparison of operating systems Terry Shannon Event