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CVE-2026-89570
cxl/mce: Make the MCE notifier per-region
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem drivers/cxl. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-89570 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 | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Flavien Solt reported lifetime issues with the CXL MCE notifier, which can lead to NULL dereferences and use-after-free in the MCE handler. The notifier was registered per memory device and stored in 'struct cxl_memdev_state', even though it only needs the region state (the region's SPA range and its extended linear cache size). Instead of keeping the memory device and endpoint alive, the correct fix is to move the notifier into 'struct cxl_region' and register it from cxl_region_probe() as it should be a per-region notifier. Setup the registration to only happen for regions that have an extended linear cache as that is the only current usage. Remove cxl_port_get_spa_cache_alias() as it is now dead code. [ dj: Update dev_warn() when notifier fails due to kconfig. (Ben) ]
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/cxl/core/mbox.c
drivers/cxl/core/mce.c
drivers/cxl/core/region.c
drivers/cxl/cxl.h
drivers/cxl/cxlmem.h
- What this is
- COMPUTE EXPRESS LINK (CXL)MAINTAINERS section matched on drivers/cxl/ · linux-cxl@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_CXL_BUS /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 armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, i386/686, i386/686-pae, i386/rt/686-pae
- trixieYnot built on armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, s390x/s390x
- forky, sidYnot built on armhf/armmp, armhf/armmp-lpae, loong64/loong64, s390x/s390x
- Y
- built in where it is built at all; some flavours do not build it
- Build switch
- CONFIG_CXL_BUS
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
- 2026-09-11 (37 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
- 0.17%, higher than 5.8% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/cxl
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.15 | 6.18.51 | 5563db13c952 |
| 6.15 | 7.2.4 | 491d8c9ac98d |
| 6.15 | 7.3 | 775d0f4558f4 |
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
- cxl_handle_mce() is invoked from the host x86 MCE decode chain (mce_gen_pool_process() workqueue) after a local machine check; it is not reached from a network protocol, Bluetooth/WiFi, or USB handler. Local access to a CXL Type-3 host is the applicable vector (higher severity than Physical).
- AC:LAttack complexity, low
- The notifier is registered on the PCI device before cxlds->cxlmd is set and while cxlmd->endpoint is ERR_PTR(-ENXIO); cxl_memdev_unregister() never NULLs cxlmd, so probe/AER/unbind leaves a dangling pointer while the notifier stays registered. Any later MCE with a usable address hits the UAF/NULL deref deterministically; EINJ/mce-inject also make the trigger attacker-controlled.
- PR:LPrivileges required, low
- cxl_handle_mce() has no capability check; cxl_pci probe installs the notifier automatically. CXL Type-3 capacity is ordinary System RAM any unprivileged local user can allocate, and async probe, cxl_mem not-yet-bound (ERR_PTR endpoint), or AER-driven detach create the bad lifetime state without init-namespace root, matching CVE-2024-26762.
- UI:NUser interaction, none
- MCE decode and CXL probe/unbind/AER recovery run in kernel workqueues with no victim mount, file open, or other interactive action; the attacker (or automatic error handling) drives the path themselves.
- S:UScope, unchanged
- The NULL dereference and use-after-free corrupt host kernel CXL/MCE state in the same OS security authority. This is standard kernel memory corruption/privilege escalation, not a KVM/IOMMU/sandbox boundary crossing.
- C:HConfidentiality impact, high
- The handler dereferences mds->cxlds.cxlmd and cxlmd->endpoint (and walks endpoint->regions) after those objects can be freed, a use-after-free that can be reclaimed to expose kernel memory. CVSS kernel guidance treats UAF as High confidentiality impact.
- I:HIntegrity impact, high
- The same UAF is groomable for an arbitrary write. The callback also computes spa_alias from the dangling objects and calls memory_failure()/set_mce_nospec() on that PFN, so a sprayed cxl_memdev/region can offline attacker-chosen pages and hijack control flow.
- A:HAvailability impact, high
- NULL deref of cxlmd, walking an ERR_PTR endpoint, and UAF of freed memdev/port/region objects cause a kernel oops/panic in the MCE workqueue; UAFs also crash even when not fully exploited.