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CVE-2026-74702
vhost-scsi: reject feature changes after endpoint
Published 2026-08-22 (2 months ago) by the Linux kernel CNA. Subsystem drivers/vhost. Debian urgency: unimportant.
Debian does not build this code. The per-release build detail is under "Where it lives" below.
What to do, per Debian release
Debian's own status for CVE-2026-74702 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
vhost_scsi_setup_vq_cmds() runs from VHOST_SCSI_SET_ENDPOINT and allocates each command's protection scatterlist array (prot_sgl) according to the acknowledged VIRTIO_SCSI_F_T10_PI bit. The command pools are not rebuilt when VHOST_SET_FEATURES changes that bit later. Although virtio feature bits must not change after feature negotiation, vhost_scsi_set_features() currently accepts such a request after the endpoint is active and updates acked_features. Enabling T10-PI after endpoint setup therefore leaves prot_sgl NULL while the I/O path follows the new feature bit. For a 129-page protection payload, vhost_scsi_mapal() passes the missing first chunk to sg_alloc_table_chained(): sg_alloc_table_chained(table, 129, first_chunk=NULL, nents_first_chunk=inline_sg_cnt) sg_pool_index() then hits: BUG_ON(nents > SG_CHUNK_SIZE); /* 129 > 128 */ The kernel reported the following call trace and register state: Call Trace: <TASK> ? __sg_alloc_table+0x1d8/0x250 ? __pfx_vhost_run_work_list+0x10/0x10 [vhost] sg_alloc_table_chained+0x59/0xf0 ? __pfx_sg_pool_alloc+0x10/0x10 ? vhost_scsi_calc_sgls.constprop.0+0x43/0x60 [vhost_scsi] vhost_scsi_handle_vq+0xf02/0x1700 [vhost_scsi] ? __pfx_vhost_scsi_handle_vq+0x10/0x10 [vhost_scsi] vhost_scsi_handle_kick+0x37/0x50 [vhost_scsi] vhost_run_work_list+0x8e/0xd0 [vhost] vhost_task_fn+0xe1/0x210 ret_from_fork+0x348/0x540 </TASK> RIP: 0010:0x4 CR2 = 0x4 RSP: 0018:ffffc90000dbf940 EFLAGS: 00010202 RAX: ffffffff82396810 RBX: ffff88811dc28b80 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000820 RDI: 0000000000000081 VHOST_F_LOG_ALL is a vhost-specific runtime feature and remains the only exception. Reject changes to any feature other than VHOST_F_LOG_ALL while the endpoint is active. This preserves the existing runtime log toggle while preventing feature-dependent command resources and data-path state from becoming inconsistent. Userspace must clear the endpoint before changing any other negotiated feature and set the endpoint up again afterward.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/vhost/scsi.c
- What this is
- VIRTIO HOST (VHOST-SCSI)MAINTAINERS section matched on drivers/vhost/scsi.c · virtualization@lists.linux.dev · Maintained
- Kernel module
- none to look for. The file would have gone into vhost_scsi, and Debian does not compile it into that module, so finding vhost_scsi in lsmod would say nothing about this CVE.
Check it on the machine
grep -wE 'CONFIG_VHOST|CONFIG_VHOST_IOTLB|CONFIG_VHOST_RING|CONFIG_VHOST_SCSI' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian does not build this code. In 4 releases below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.
- bookworm, trixie, forky, sidn
- n
- not enabled on any flavour - this release does not build the code
- Build switches
- CONFIG_VHOST, CONFIG_VHOST_IOTLB, CONFIG_VHOST_RING, CONFIG_VHOST_SCSI
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-22 (2 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 6.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/vhost
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.15 | 6.18.45 | a06e4611d455 |
| 6.15 | 7.1.9 | 9a3eb77a612f |
| 6.15 | 7.2 | 42bc45df5905 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- vhost-scsi is only reachable through virtio-scsi virtqueue kicks and VHOST_* ioctls on /dev/vhost-scsi by the VMM or a VM guest; it is not exposed via any network protocol or remote packet path.
- AC:LAttack complexity, low
- Once VIRTIO_SCSI_F_T10_PI is toggled after VHOST_SCSI_SET_ENDPOINT, a virtio-scsi request with protection data spanning 129+ pages deterministically drives vhost_scsi_mapal() into sg_alloc_table_chained() with NULL prot_sgl and triggers BUG_ON(nents > SG_CHUNK_SIZE); no races or victim-specific memory layout are required.
- PR:LPrivileges required, low
- No host root or CAP_SYS_ADMIN is needed: an unprivileged cloud VM tenant can negotiate virtio-scsi T10-PI (QEMU propagates VHOST_SET_FEATURES) and submit the oversized PI I/O, and vhost ioctls have no capability gate for any process holding the vhost-scsi fd.
- UI:NUser interaction, none
- Exploitation requires only attacker-controlled virtio-scsi I/O and/or VMM feature updates during normal VM operation; no administrator or end-user action beyond routine VM use is needed.
- S:CScope, changed
- On KVM hosts using virtio-scsi with the vhost backend, a malicious guest reaches host-kernel vhost-scsi worker code and can panic the hypervisor, crossing the guest-to-host virtual machine security boundary.
- C:HConfidentiality impact, high
- Enabling T10-PI after endpoint setup leaves prot_sgl NULL while the data path allocates and maps protection scatterlists from the shared sg pool; the reporter hit a fault at address 0x4, and smaller requests can complete with mismatched inline/pool metadata that corrupts kernel heap bookkeeping on free.
- I:HIntegrity impact, high
- Attacker-controlled protection iterators are mapped into kernel scatterlists passed to the LIO/TCM target stack under inconsistent feature state, yielding heap writes and unreliable sg_free_table_chained() teardown that can be leveraged for control-flow hijack beyond the immediate BUG_ON.
- A:HAvailability impact, high
- The demonstrated path hits BUG_ON(nents > SG_CHUNK_SIZE) in sg_pool_index() from the vhost worker during vhost_scsi_handle_vq(), producing a host kernel oops/panic that terminates the hypervisor and all co-resident VMs.