DEBIAN-CVE-2026-99155: Debian/linux vulnerability

In the Linux kernel, the following vulnerability has been resolved: scsi: xen/scsifront: Check for a NULL shadow entry on a backend response scsifrontdoresponse() validates the rqid in a backend response against VSCSIIFMAXREQS before using it to index info->shadow[], but then dereferences the entry to test ->inflight without checking that the slot is populated. Shadow slots are NULL before a command is submitted (the host private area is zeroed at allocation) and are reset to NULL in scsifrontputrqid() once a request completes, so an in-range rqid that does not correspond to an outstanding request makes the frontend dereference a NULL pointer. A malicious or buggy backend can thus crash the guest by returning a response whose rqid is in range but not in flight -- for example a spurious response before any command has been issued, or a duplicate of one already completed. The ring has only VSCSIIFMAXREQS (16) slots, so before the first command every in-range rqid selects a NULL slot. Reject a response whose shadow slot is not populated.