CVE-2026-99155
Received Received - Intake

NULL Pointer Dereference in Linux Kernel Xen scsifront Driver

Publication date: 2026-10-28

Last updated on: 2026-10-28

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: scsi: xen/scsifront: Check for a NULL shadow entry on a backend response scsifront_do_response() validates the rqid in a backend response against VSCSIIF_MAX_REQS 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 _scsifront_put_rqid() 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 VSCSIIF_MAX_REQS (16) slots, so before the first command every in-range rqid selects a NULL slot. Reject a response whose shadow slot is not populated.

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Meta Information

Published
2026-10-28
Last Modified
2026-10-28
Generated
2026-10-28
AI Q&A
2026-10-28
EPSS Evaluated
N/A
NVD
CVE-2026-99155
EUVD
EUVD-2026-111907

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
Linux Linux 6d1c2f48f3fcf5f42967938c8ba6b42ac6b44b43
Linux Linux 6d1c2f48f3fcf5f42967938c8ba6b42ac6b44b43
Linux Linux 6d1c2f48f3fcf5f42967938c8ba6b42ac6b44b43
Linux Linux 5.19

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a NULL pointer dereference vulnerability in the Linux kernel's Xen SCSI frontend driver. It occurs when processing backend responses. The driver validates a response's request ID (rqid) against a maximum limit but fails to check if the corresponding shadow entry is populated before dereferencing it. A malicious or buggy backend can exploit this by sending a response with a valid but unused rqid, causing a crash due to NULL pointer access.

Detection Guidance

This vulnerability is specific to the Linux kernel's scsi frontend driver for Xen (scsifront). Detection requires checking if your system is running a vulnerable kernel version. Examine kernel logs for NULL pointer dereference errors related to scsifront or scsi operations. Commands like 'dmesg | grep -i scsi' or 'journalctl -k | grep -i null' may help identify crashes or errors.

Impact Analysis

If you use a Linux system with Xen virtualization and SCSI devices, this vulnerability could allow a malicious or compromised backend to crash your guest VM. This leads to denial of service, potential data loss, or unauthorized access if the crash exposes sensitive information. Systems without Xen SCSI frontend are unaffected.

Mitigation Strategies

Apply the latest kernel update provided by your Linux distribution to patch this issue. If immediate patching is not possible, consider disabling the Xen scsifront driver if unused. Monitor vendor advisories for kernel updates addressing this CVE. Restrict access to Xen backend domains to trusted sources to reduce attack surface.

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