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CVE-2026-89731
cxl/ras: Fix cxl_rch_get_aer_info() out-of-bounds AER register read
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-2026-89731 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 | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| 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. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
cxl_rch_get_aer_info() copies the RCH Downstream Port AER capability from the RCRB MMIO block using a readl() loop bounded by sizeof(struct aer_capability_regs). This struct is a software layout and its embedded struct pcie_tlp_log is larger than the on-wire AER capability. As a result the loop reads past the mapped AER register block. The over-read also populates the software-only tail fields including header_log.header_len. An out-of-range header_len passed to pcie_print_tlp_log() can then loop past the header log buffer and cause a second out-of-bounds read. The read was correct when introduced, but struct pcie_tlp_log has since grown (Header Log and TLP Prefix Log sizes, header_len and flit fields), so sizeof(struct aer_capability_regs) no longer matches the physical AER capability. Bound the read to the physical AER registers, header through the 16 byte Header Log. Zero the destination first so the software-only fields are deterministic.
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/ras_rch.c
- 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 -wE 'CONFIG_CXL_BUS|CONFIG_CXL_RAS|CONFIG_PCIEAER_CXL' /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. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookworm?
- 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, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- bookworm · linux-6.12Ynot built on armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp
- ?
- not established - no Makefile entry for the affected file
- Y
- built in where it is built at all; some flavours do not build it
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_CXL_BUS, CONFIG_CXL_RAS, CONFIG_PCIEAER_CXL
- 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
- 2026-09-11 (37 days ago)source
- CVSS
- 7.1 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.16%, higher than 5.2% 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 |
|---|---|---|
| 6.7 | 6.12.111 | 7f5a2a330dde |
| 6.7 | 6.18.51 | 8bd3523df131 |
| 6.7 | 7.2.4 | 8e3d9dbb25d3 |
| 6.7 | 7.3 | 29458e62d082 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | 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 vulnerable cxl_rch_get_aer_info() runs only from the host PCI AER IRQ path (aer_isr → cxl_rch_handle_error → cxl_error_detected/cxl_cor_error_detected) on Restricted CXL Host/Device topologies; it is not reachable from network protocols. Local access to a CXL host is the applicable vector and is higher severity than physical card insertion.
- AC:LAttack complexity, low
- Once an RCH downstream-port AER event is raised, the readl() loop copies sizeof(struct aer_capability_regs) (100 bytes) instead of the 44-byte physical Header Log with no race. Unimplemented RCRB MMIO commonly returns 0xFFFFFFFF, so header_len/flit reliably drive a second out-of-bounds read in pcie_print_tlp_log().
- PR:LPrivileges required, low
- The AER ISR and CXL error handlers perform no capability check. An unprivileged local user, or a guest with a passed-through CXL endpoint, can induce CXL protocol/AER errors that reach this path; init-namespace root is not required.
- UI:NUser interaction, none
- PCIe AER interrupts are dispatched automatically by aer_isr() into the CXL PCI error handlers; no victim mount, file open, or other interactive action is required.
- S:UScope, unchanged
- The MMIO and stack out-of-bounds reads occur in the host kernel CXL/PCI AER code and do not cross a VM, IOMMU, or sandbox security boundary.
- C:HConfidentiality impact, high
- Adjacent RCRB MMIO is copied into software-only fields including header_log.header_len; pcie_print_tlp_log() then reads log->dw[] with a u8 index up to 255 past the 14-dword array, leaking up to ~1KB of kernel stack and RCRB contents to dmesg.
- I:NIntegrity impact, none
- Both issues are out-of-bounds reads only: MMIO is copied into a correctly sized stack aer_capability_regs, and pcie_print_tlp_log() only reads log->dw[]. In-bounds status writel()s and length-capped scnprintf() provide no write or control-flow primitive.
- A:HAvailability impact, high
- The unbounded stack read in pcie_print_tlp_log() and readl() past the physical AER capability in the RCRB can fault or raise a platform machine-check, producing a kernel oops/panic; uncorrectable CXL RAS handling can also disable CXL.mem.