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CVE-2026-80551
s390/vfio_ccw: Ensure first IDAW remains constant
Published 2026-08-26 (2 months ago) by the Linux kernel CNA. Subsystem drivers/s390. Debian urgency: not yet assigned.
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-2026-80551 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixed | 6.12.105-1 | Update the kernel and reboot. Fixed in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The first IDAW in a list does not need to be on a 2K/4K boundary like all others, and so is read separately to accurately calculate the size of the buffer needed to read the full IDAL. Verify that the address found in the first IDAW is unchanged between reads, to ensure a consistent set of IDAWs being worked with.
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/s390/cio/vfio_ccw_cp.c
drivers/s390/cio/vfio_ccw_cp.h
- What this is
- S390 VFIO-CCW DRIVERMAINTAINERS section matched on drivers/s390/cio/vfio_ccw* · linux-s390@vger.kernel.org · Supported
Check it on the machine
grep -wE 'CONFIG_S390|CONFIG_VFIO_CCW' /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 5 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, sid, bookworm · linux-6.12n
- n
- not enabled on any flavour - this release does not build the code
- Build switches
- CONFIG_S390, CONFIG_VFIO_CCW
- 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
- 2026-08-26 (2 months ago)source
- CVSS
- 9.3 critical
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.20%, higher than 8.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/s390
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.3 | 6.6.154 | 460b977a4e71 |
| 5.3 | 6.12.105 | 0d46c2565f17 |
| 5.3 | 6.18.46 | 08ef2a821156 |
| 5.3 | 7.1.10 | fc59e9482117 |
| 5.3 | 7.2 | 565bef268d75 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
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
- The flaw is reached only via local VFIO-ccw mediated-device write()/ioctl on the I/O region (QEMU relaying guest SSCH/channel programs into fsm_io_request→cp_prefetch→ccwchain_fetch_ccw); vfio-ccw has no network, adjacent-radio, or physical-bus entry point.
- AC:LAttack complexity, low
- The malicious guest fully controls guest IDAL memory and can mutate the first IDAW between ccw_count_idaws() and get_guest_idal() using another vCPU and repeated I/O submissions; the attacker controls both sides of this TOCTOU window without uncontrollable host layout or timing luck.
- PR:NPrivileges required, none
- A malicious VM guest with an assigned vfio-ccw mediated subchannel needs no host credentials or capabilities; it only issues guest channel programs with IDA CCWs that QEMU forwards into cp_prefetch(), requiring none of the administrator privileges used to create the mdev.
- UI:NUser interaction, none
- Exploitation requires only the attacker's own guest channel program submission through normal passthrough I/O; no separate victim mount, click, or user action is needed once the device is assigned.
- S:CScope, changed
- Guest-supplied IDAL channel programs are parsed and translated in the host kernel during cp_prefetch(), so inconsistent IDAW handling crosses the guest-to-host VFIO device-passthrough boundary and can compromise the hypervisor and co-resident VMs.
- C:HConfidentiality impact, high
- If the first IDAW changes between reads, idaw_nr can be under-counted and page_array_pin() may omit guest pages while hardware DMA still runs, enabling reads of unpinned host kernel memory and disclosure beyond the guest boundary.
- I:HIntegrity impact, high
- Mismatched IDAW sizing lets a guest craft channel programs that pin one set of pages but execute I/O against another, causing host memory corruption via misdirected DMA and supporting further arbitrary-write or control-flow hijack primitives.
- A:HAvailability impact, high
- Inconsistent IDAL translation can immediately fault the host kernel during page pinning or channel I/O completion, and repeated guest-triggered SSCH submissions can reliably panic or hang the hypervisor and all co-hosted VMs.