Xen XSA-122 Bug: Analysis & Limitations

This report analyzes XSA-122, a 2015 Xen hypervisor vulnerability in the HYPERVISOR_xen_version hypercall that can leak up to small amounts of hypervisor stack memory (practically limited to ~144 bytes of useful data and a 1024-byte reserved stack area). The author demonstrates how the leak is triggered from PV and HVM guests with kernel privileges, describes affected sub-operations (compile_info, extraversion, changeset), and concludes the bug has limited exploitability and utility for attackers despite being an interesting research finding.