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CVE-2026-74439
iommu/vt-d: Clear Present bit before tearing down scalable-mode context entry
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-2026-74439 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 | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
device_pasid_table_teardown() zeroes the 128-bit scalable-mode context entry with context_clear_entry() while the Present bit is still set. This creates a window where the hardware can fetch a torn entry, with some fields already zeroed while Present is still set, leading to unpredictable behavior or spurious faults. The context-cache invalidation is issued only after the entry has been zeroed, and intel_pasid_free_table() then frees the PASID directory pages, so the IOMMU can keep walking a stale Present=1 entry that points at freed memory. While x86 provides strong write ordering, the compiler may reorder the two 64-bit writes to the entry, and the hardware fetch is not guaranteed to be atomic with respect to multiple CPU writes. Commit c1e4f1dccbe9d ("iommu/vt-d: Clear Present bit before tearing down context entry") fixed this exact pattern in domain_context_clear_one() and the copied-context path, but device_pasid_table_teardown() was not converted. Align it with the "Guidance to Software for Invalidations" in the VT-d spec, Section 6.5.3.3, using the same ownership handshake as the sibling fix: clear only the Present bit, flush it to the IOMMU, perform the context-cache invalidation, and only then zero the rest of the entry.
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/intel/pasid.c
- What this is
- INTEL IOMMU (VT-d)MAINTAINERS section matched on drivers/iommu/intel/ · iommu@lists.linux.dev · Supported
Check it on the machine
grep -w CONFIG_INTEL_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 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 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 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_INTEL_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
- 2026-08-15 (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
- 0.20%, higher than 8.6% 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 |
|---|---|---|
| 6.9 | 6.12.97 | e9e83bcfe37d |
| 6.9 | 6.18.40 | 588718101e84 |
| 6.9 | 7.1.5 | 7fd4077dc92b |
| 6.9 | 7.2 | f46452c3df7a |
| 6.8.2 | 0 | 0 |
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 in Intel VT-d scalable-mode PASID context teardown reached only via local kernel IOMMU device-release paths (intel_iommu_release_device → device_pasid_table_teardown), triggered by PCI hot-unplug, sysfs driver unbind, or iommu deinit—not by any network-facing protocol.
- AC:LAttack complexity, low
- This is a use-after-free where intel_pasid_free_table() frees PASID directory pages while the IOMMU may still cache a Present=1 context entry; an attacker controlling a PASID-capable device can keep DMA active and time bus removal/teardown to hit the stale-entry window reliably (AC:L per UAF guidance).
- PR:NPrivileges required, none
- A malicious PASID-capable PCIe device can trigger the vulnerable intel_iommu_release_device teardown by physical hot-unplug (pci_stop_and_remove_bus_device) while sustaining DMA, requiring no authenticated host account or capability on the target system.
- UI:NUser interaction, none
- No victim interaction is required beyond the attacker's own device removal or driver-unbind orchestration; the vulnerable teardown executes automatically once the PCI/IOMMU release path runs.
- S:CScope, changed
- A stale or torn scalable-mode context entry breaks VT-d DMA isolation—the IOMMU can translate device DMA against freed PASID table memory, crossing the device/host (or guest/host) IOMMU security boundary per kernel IOMMU bypass guidance.
- C:HConfidentiality impact, high
- With the IOMMU walking freed PASID directory pages, a controlled device can DMA-read host physical memory outside its assigned domain, yielding arbitrary cross-boundary read disclosure (C:H; UAF enables attacker influence over translation contents).
- I:HIntegrity impact, high
- The same mistranslation gives the device an arbitrary DMA write primitive against host memory outside its domain, enabling data modification and potential control-flow hijack via memory corruption (standard UAF/IOMMU-bypass I:H guidance).
- A:HAvailability impact, high
- The commit documents unpredictable behavior and spurious DMAR faults from torn Present entries; freed PASID tables under active IOMMU walks can fault-storm, hang, or panic the host—any kernel crash/UAF qualifies as A:H.