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CVE-2026-98254
swiotlb: use the adjusted address for the highmem page lookup
Published 2026-10-06 (13 days ago) by the Linux kernel CNA. Subsystem kernel/dma. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-98254 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 | fixedDSA-6568-1 · 2026-10-16 · text | 6.12.113-1 | Update the kernel and reboot. DSA-6568-1 shipped the fix on 2026-10-16, in 6.12.113-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.8-1 | Update the kernel and reboot. Fixed in 7.2.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.8-1 | Update the kernel and reboot. Fixed in 7.2.8-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
swiotlb_bounce() reads the page frame number from the slot's recorded orig_addr, then advances orig_addr by tlb_offset to reach the address the caller asked about. The highmem branch mixes the two: the offset within the page comes from the adjusted address, the page from the value before it. Once the adjustment crosses a page boundary the pair no longer describes one location, and the whole copy lands one page below the intended one for a positive tlb_offset, one above for a negative one. DMA_FROM_DEVICE writes the device data over the wrong page and leaves the intended one stale, DMA_TO_DEVICE feeds the device from a page the mapping may not cover. Partial syncs through dma_sync_single_range_for_*() are what make tlb_offset non-zero. The branch test is picked the same way, so a slot recorded in lowmem can be adjusted into highmem and the lowmem path then hands a highmem address to phys_to_virt(). Take both from orig_addr once it is final and keep pfn in the branch that uses it. PhysHighMem() asks the question straight from the address, as dma-debug already does.
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.
kernel/dma/swiotlb.c
- What this is
- DMA MAPPING HELPERSMAINTAINERS section matched on kernel/dma/ · iommu@lists.linux.dev · Supported
Check it on the machine
grep -w CONFIG_SWIOTLB /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 i386/686
- trixieYnot built on armel/rpi
- forky, sidy
- Y
- built in where it is built at all; some flavours do not build it
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_SWIOTLB
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
- 2026-10-06 (13 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.14%, higher than 2.8% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- kernel/dma
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.13 | 6.12.112 | 6e53b4d6afbd |
| 5.13 | 6.18.54 | aa4709813b29 |
| 5.13 | 7.2.8 | 0219b72f5c20 |
| 5.13 | 7.3 | b7d7914a9ae3 |
| 5.10.47 | 0 | 0 |
| 5.12.14 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DSA-6568-1 | 2026-10-16 | trixie 6.12.113-1 | 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 defect is in swiotlb_bounce(), reached only via __swiotlb_sync_single_for_cpu/_for_device from a driver's dma_sync_single_range_for_*() on a bounced buffer. No protocol message carries malformed input, and a local user can only cause it by doing I/O on a highmem buffer through such a driver.
- AC:LAttack complexity, low
- Not used; the AC line below is the real value.
- PR:LPrivileges required, low
- The attacker needs an ordinary local account to issue I/O whose buffers (user or page-cache pages, which can be highmem) go through an affected device's streaming DMA mapping. No capability check on the swiotlb sync path stands in the way.
- UI:NUser interaction, none
- Once the attacker's own I/O drives the partial-sync pattern, no victim action is needed. The bounce runs inside the driver's sync call.
- S:UScope, unchanged
- The bad copy is done by the kernel's own swiotlb code into kernel-managed physical memory. No IOMMU, VM or other boundary is crossed beyond the kernel's own authority.
- C:HConfidentiality impact, high
- On DMA_TO_DEVICE, memcpy_from_page() uses pfn_to_page(PFN_DOWN(old orig_addr)) and feeds the device a whole neighbouring physical page the mapping does not cover. This can expose unrelated kernel or user data to the device.
- I:HIntegrity impact, high
- On DMA_FROM_DEVICE, memcpy_to_page() writes device data over the page next to the intended one, corrupting arbitrary neighbouring memory. Separately, a lowmem slot shifted into highmem sends a highmem address to phys_to_virt() and memcpy() through a bogus pointer.
- A:HAvailability impact, high
- Overwriting an unrelated physical page, or calling memcpy() on a bogus phys_to_virt() pointer for a highmem address, can corrupt kernel state or fault and oops the kernel.