Look up another CVE · open CVE-2026-74573 in the interactive tracker
CVE-2026-74573
iommu/arm-smmu-v3-iommufd: Require exactly one Stream ID for a vDEVICE
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem drivers/iommu. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74573 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 | 7.1.8-1 | 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. |
The vulnerability
What the bug is
arm_vsmmu_vsid_to_sid() maps a guest's vSID to a single physical Stream ID taken from master->streams[0], assuming a device has exactly one stream. A device with several streams gets only its first one mapped, so a guest vSID invalidation cannot reach the others' ATC and IOTLB entries; a device with none makes master->streams a ZERO_SIZE_PTR, read out of bounds. Add an arm_vsmmu_vdevice_init() op to reject the vDEVICE with -EOPNOTSUPP when master->num_streams is not one, rather than mapping it silently.
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/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
- What this is
- ARM SMMU DRIVERSMAINTAINERS section matched on drivers/iommu/arm/ · linux-arm-kernel@lists.infradead.org · Maintained
Check it on the machine
grep -wE 'CONFIG_ARM_SMMU_V3|CONFIG_ARM_SMMU_V3_IOMMUFD' /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 2 releases. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidn
- ?
- not established - no Makefile entry for the affected file
- n
- not enabled on any flavour - this release does not build the code
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switches
- CONFIG_ARM_SMMU_V3, CONFIG_ARM_SMMU_V3_IOMMUFD
- 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
- 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
- 0.19%, higher than 8.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.13 | 6.18.44 | 3808bab5d95a |
| 6.13 | 7.1.8 | 0acbc621341a |
| 6.13 | 7.2 | c3b8ee84a965 |
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
- Exploitation requires reaching arm_vsmmu_cache_invalidate() via the IOMMU_HWPT_INVALIDATE ioctl on /dev/iommu (or VFIO-compat fd), a local syscall path from a process or VMM forwarding guest nested-IOMMU invalidations to the host kernel.
- AC:LAttack complexity, low
- Once a vDEVICE is registered on an ARM SMMUv3 vIOMMU with a multi-stream or zero-stream master, the attacker reliably issues ATC_INV/CFGI_CD invalidation commands; no race or uncontrollable memory layout is required beyond having such hardware attached.
- PR:NPrivileges required, none
- A malicious guest or tenant VM with passed-through PCI and nested vIOMMU needs no host root or credentials; QEMU normally forwards guest IOMMU invalidations to host iommufd, reaching the vulnerable code without any host authentication or admin privilege.
- UI:NUser interaction, none
- Exploitation is fully attacker-driven through iommufd ioctls and does not require any victim user action such as opening files, clicking links, or mounting filesystems beyond the attacker-controlled device setup.
- S:CScope, changed
- Incomplete vSID-to-SID mapping leaves stale ATC/IOTLB entries on additional Stream IDs, allowing device DMA to bypass the guest nested IOMMU policy and reach host physical memory outside the guest security domain—an IOMMU/DMA boundary violation.
- C:HConfidentiality impact, high
- Stale translations on un-invalidated streams let a malicious guest or local user read host memory via DMA using cached mappings; the num_streams==0 path also performs an out-of-bounds read of master->streams[0].id from ZERO_SIZE_PTR, leaking kernel memory into the SID field.
- I:HIntegrity impact, high
- Stale IOTLB/ATC entries enable arbitrary DMA writes to previously mapped host pages, and the leaked/garbage SID from the out-of-bounds streams[0] read can target invalidation at unintended Stream IDs, corrupting IOMMU translation state.
- A:HAvailability impact, high
- The zero-stream case dereferences master->streams[0] when streams is ZERO_SIZE_PTR, which can kernel-oops the host; even without a crash, stale TLB state enables sustained hostile DMA that can destabilize the system.