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CVE-2026-74515
KVM: s390: pci: Reject adapter interrupt forwarding if already enabled
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem arch/s390. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74515 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 | fixedDLA-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. 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 MPCIFC instruction doesn't allow registering adapter interrupts without first unregistering. So reject any request to enable interrupt forwarding if its already enabled for the zPCI device. This also fixes overwriting and thus leaking resources when the ioctl is called multiple times for the same device.
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.
arch/s390/kvm/pci.c
- What this is
- S390 VFIO-PCI DRIVERMAINTAINERS section matched on arch/s390/kvm/pci* · linux-s390@vger.kernel.org · Supported
- Kernel module
- kvm
Check it on the machine
grep -wE 'CONFIG_KVM|CONFIG_VFIO_PCI_ZDEV_KVM' /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.
lsmod | grep -w kvmPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian does not build this code in 2 releases. It does build it in 3 releases, so the answer depends on which release the machine runs.
- bookwormn
- trixieMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64
- forky, sidMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt-amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt-arm64, armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64
- bookworm · linux-6.12n
- n
- not enabled on any flavour - this release does not build the code
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_KVM, CONFIG_VFIO_PCI_ZDEV_KVM
- 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
- 2026-08-15 (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
- 0.13%, higher than 2.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- arch/s390
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.0 | 6.1.183 | 642d2d1067f7 |
| 6.0 | 6.6.151 | 78d9648e7e96 |
| 6.0 | 6.12.103 | 6be1ff49ba81 |
| 6.0 | 6.18.44 | 6837f0ae85fd |
| 6.0 | 7.1.8 | 591952b63a9f |
| 6.0 | 7.2 | 8fa01be5a614 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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 bug is reached only through the KVM_S390_ZPCI_OP VM ioctl in arch/s390/kvm/kvm-s390.c; on IBM Z with zPCI passthrough, QEMU forwards guest mpcifc adapter-interrupt registration to this local ioctl path, not over the network.
- AC:LAttack complexity, low
- An attacker with an assigned zPCI device can call KVM_S390_ZPCIOP_REG_AEN twice in a row without racing or special memory layout; each duplicate call deterministically re-enters kvm_s390_pci_aif_enable() and overwrites host bookkeeping.
- PR:LPrivileges required, low
- Exploitation requires a KVM VM file descriptor and a VFIO-assigned zPCI device, i.e. control of the guest/VMM process (typical cloud tenant or qemu user), not init-namespace root; this cannot be reached from an unprivileged user namespace alone.
- UI:NUser interaction, none
- Once zPCI passthrough is configured, the guest or its VMM can issue duplicate registration on its own; no additional host administrator or victim user action is needed beyond normal device setup.
- S:CScope, changed
- A guest-triggered ioctl corrupts host-owned AIFT/GAITE state outside the VM security boundary, leaving orphaned summary-index entries that the host interrupt path later dereferences in hypervisor context.
- C:HConfidentiality impact, high
- Duplicate enable overwrites zdev->aisb and leaks earlier GAITE/AIBV resources; on teardown aift->kzdev[orphaned_si] still points at freed kvm_zdev/kvm, so aen_host_forward() performs UAF reads of host hypervisor memory.
- I:HIntegrity impact, high
- Stale orphaned GAITE entries retain guest-chosen physical addresses and dangling kzdev pointers; aen_host_forward() can execute set_bit_inv() and further host-side writes through those corrupted structures during adapter-event delivery.
- A:HAvailability impact, high
- Each duplicate REG_AEN leaks pinned guest pages, AIBV allocations, and summary bits without rollback when MPCIFC re-registration fails, enabling repeatable host memory exhaustion and kernel oops/panic via IRQ-time UAF dereferences.