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CVE-2026-43253
iommu/amd: move wait_on_sem() out of spinlock
Published 2026-05-06 (5 months ago) by the Linux kernel CNA. Subsystem drivers/iommu. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-43253 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 | 6.12.85-1 | Update the kernel and reboot. Fixed in 6.12.85-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 6.19.6-1 | Update the kernel and reboot. Fixed in 6.19.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.19.6-1 | Update the kernel and reboot. Fixed in 6.19.6-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
With iommu.strict=1, the existing completion wait path can cause soft lockups under stressed environment, as wait_on_sem() busy-waits under the spinlock with interrupts disabled. Move the completion wait in iommu_completion_wait() out of the spinlock. wait_on_sem() only polls the hardware-updated cmd_sem and does not require iommu->lock, so holding the lock during the busy wait unnecessarily increases contention and extends the time with interrupts disabled.
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/iommu/amd/iommu.c
- What this is
- AMD IOMMU (AMD-VI)MAINTAINERS section matched on drivers/iommu/amd/ · iommu@lists.linux.dev · Maintained
Check it on the machine
grep -w CONFIG_AMD_IOMMU /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 builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormYnot built on amd64/cloud-amd64, arm64/arm64, arm64/cloud-arm64, arm64/rt/arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, i386/686, i386/686-pae, i386/rt/686-pae, ppc64el/powerpc64le
- trixieYnot built on amd64/cloud-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, s390x/s390x
- forky, sidYnot built on amd64/cloud-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, s390x/s390x
- Y
- built in where it is built at all; some flavours do not build it
- Build switch
- CONFIG_AMD_IOMMU
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
- 2026-05-06 (5 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.49%, higher than 40.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/iommu
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.9 | 6.6.128 | f2f65b28d802 |
| 4.9 | 6.12.75 | 715c263119fd |
| 4.9 | 6.18.16 | e15768e68820 |
| 4.9 | 6.19.6 | 496269d12072 |
| 4.9 | 7.0 | d2a0cac10597 |
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:NAttack vector, network
- On AMD systems where the IOMMU protects a PCIe NIC, received packets can drive NIC RX cleanup through DMA unmap, IOTLB sync, amd_iommu_iotlb_sync(), iommu_completion_wait(), and wait_on_sem(). A remote peer can generate this traffic without local system access.
- AC:LAttack complexity, low
- Triggering requires sustained IOMMU flush pressure, but the attacker can create that pressure by sending traffic and no uncontrollable race, memory layout, or victim action is needed. The affected AMD IOMMU/translated-DMA deployment is assumed for scoring.
- PR:NPrivileges required, none
- The highest reasonable path is unauthenticated network receive processing on an internet-facing server NIC. No local account, capability, or namespace access is required to cause packet-driven DMA cleanup.
- UI:NUser interaction, none
- No victim user action is required once the affected system is running and receiving network traffic. The kernel/NIC interrupt and NAPI paths process packets automatically.
- S:UScope, unchanged
- The issue causes a host-kernel availability failure within the same security authority. It does not bypass IOMMU/DMA isolation, escape a VM, or cross into another security scope.
- C:NConfidentiality impact, none
- The bug is a busy wait under a spinlock with interrupts disabled while polling a hardware-updated command semaphore. There is no memory corruption, out-of-bounds read, or information disclosure primitive.
- I:NIntegrity impact, none
- The vulnerable path does not corrupt memory or provide an attacker-controlled write. It only causes excessive locked/IRQ-disabled waiting during IOMMU command completion.
- A:HAvailability impact, high
- The fix and related reports describe soft lockups/RCU stalls caused by wait_on_sem() spinning while holding the IOMMU lock with interrupts disabled. Repeated triggering can hang or severely stall the kernel, so availability impact is high.