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CVE-2026-74703
vhost-scsi: Validate T10 PI scatterlist counts
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-2026-74703 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
When T10 PI is negotiated, vhost-scsi splits protection bytes from the data iterator before mapping the request scatterlists. A malformed request can claim protection bytes that cover or exceed the full payload length. The former leaves no data bytes to map, while the latter underflows exp_data_len before advancing the iterator. Both cases can let a zero data SGL count reach sg_alloc_table_chained(), which triggers BUG_ON(!nents). Reject protection lengths that cover or exceed the payload before subtracting prot_bytes and advancing the iterator. Also propagate negative errors from the protection SGL calculation before calling the allocator, matching the data SGL path.
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
- 7.1 high
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.18%, higher than 7.4% 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 | 2417a498cf3f |
| 6.15 | 7.1.9 | f8fe3f8d342d |
| 6.15 | 7.2 | d876c493fc4b |
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
- A malicious KVM guest reaches vhost_scsi_handle_vq() by kicking the virtio-scsi I/O virtqueue; vhost_get_vq_desc() and copy_from_iter_full() pull a guest-controlled virtio_scsi_cmd_req_pi header into the host kernel, not via any network-facing protocol.
- AC:LAttack complexity, low
- With VIRTIO_SCSI_F_T10_PI negotiated, the guest fully controls pi_bytesout/pi_bytesin and descriptor payload sizes; setting protection bytes to cover or exceed the payload deterministically leaves zero data SGL entries and hits BUG_ON(!nents) without races or uncontrollable memory layout.
- PR:NPrivileges required, none
- No host root or capabilities are required; a malicious VM tenant only needs code execution inside a guest with an active virtio-scsi/vhost-scsi endpoint (standard QEMU/KVM+LIO passthrough), matching other guest-to-host virtio/KVM CNA scores for cloud multi-tenant hosts.
- UI:NUser interaction, none
- No separate victim action is needed; the attacker submits crafted virtio-scsi requests and kicks the virtqueue from their own guest workload without requiring a host administrator or another user to mount storage or perform any interactive step.
- S:CScope, changed
- Guest-supplied virtio-scsi T10 PI requests trigger BUG_ON(!nents) in host sg_alloc_table_chained() during vhost_scsi_mapal(), panicking the physical host kernel and crossing the KVM guest-to-host virtualization security boundary.
- C:NConfidentiality impact, none
- The failure mode is an explicit BUG_ON(!nents) on zero scatterlist count; there is no demonstrated out-of-bounds read, use-after-free, or other memory corruption before the panic that could disclose host kernel data.
- I:NIntegrity impact, none
- No guest-controlled host memory write or control-flow hijack occurs; the host kernel aborts via BUG_ON before target_submit_prep(), and the bug is invalid scatterlist accounting rather than exploitable heap corruption.
- A:HAvailability impact, high
- BUG_ON(!nents) in sg_alloc_table_chained() provokes a host kernel oops/panic in the vhost worker during guest virtio-scsi I/O, denying availability of the hypervisor and all co-resident VMs; the attack is reliably repeatable with crafted PI headers.