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CVE-2026-93079
cxl/features: Reject Get Feature count larger than the output buffer
Published 2026-09-17 (31 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-2026-93079 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
cxlctl_get_feature() sizes its output buffer from the user's fwctl_rpc.out_len, but the device is told to write cxl_mbox_get_feat_in.count bytes into rpc_out->payload, which is a separate user-controlled value. Nothing bounds count against out_len, so a small out_len with a large count overflows the kvzalloc()'d buffer. A heap OOB write reachable from FWCTL_RPC. Reject requests where count exceeds the available payload room, before allocating.
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/features.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_FEATURES' /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_CXL_BUS, CONFIG_CXL_FEATURES
- 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
- 2026-09-17 (31 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 6.3% 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 | 6.18.52 | 3f02031a0a53 |
| 6.15 | 7.2.6 | 329ea475581c |
| 6.15 | 7.3 | 4bf6bac37507 |
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 overflow is triggered by ioctl(FWCTL_RPC) on /dev/fwctl/fwctlN via fwctl_fops_ioctl()->fwctl_cmd_rpc()->cxlctl_fw_rpc()->cxlctl_get_feature(). The mismatched inputs are local userspace fields fwctl_rpc.out_len and cxl_mbox_get_feat_in.count on a CXL_MBOX_OP_GET_FEATURE (0x0501) RPC, not bytes from a network or CXL-peer protocol message.
- AC:LAttack complexity, low
- The caller sets both fwctl_rpc.out_len and get_feat_in.count in one GET_FEATURE RPC. cxlctl_get_feature() kvzallocs out_len then passes count to cxl_get_feature() as the mailbox output length, so a short out_len with count larger than the payload room overflows on memcpy_fromio() in __cxl_pci_mbox_send_cmd(). Feature size is learned first via GET_SUPPORTED_FEATURES; no race is required.
- PR:LPrivileges required, low
- CXL_MBOX_OP_GET_FEATURE is accepted at FWCTL_RPC_CONFIGURATION; fwctl_cmd_rpc() checks CAP_SYS_RAWIO only for FWCTL_RPC_DEBUG_WRITE_FULL, and cxlctl_open_uctx() is a no-op. Opening /dev/fwctl/fwctlN is sufficient, and that node is routinely granted to management/VMM users without init-namespace root.
- UI:NUser interaction, none
- The attacker opens /dev/fwctl/fwctlN and issues ioctl(FWCTL_RPC) with opcode CXL_MBOX_OP_GET_FEATURE themselves; no victim action such as mounting a volume or opening a file is required.
- S:UScope, unchanged
- __cxl_pci_mbox_send_cmd() memcpy_fromio()s the Get Feature mailbox payload into the host kernel heap object rpc_out->payload allocated by cxlctl_get_feature(). The corruption stays in the host kernel CXL/fwctl path and is not a guest-to-host, IOMMU, or other changed-scope boundary.
- C:HConfidentiality impact, high
- cxl_get_feature() tells the device to write get_feat_in.count bytes (u16, up to 65535) into rpc_out->payload, overflowing the kvzalloc(out_len) object via memcpy_fromio(). That heap out-of-bounds write is memory corruption that can be turned into an arbitrary-read primitive.
- I:HIntegrity impact, high
- The same GET_FEATURE path is a kernel heap out-of-bounds write: __cxl_pci_mbox_send_cmd() copies the mailbox payload into feat_out past the end of the out_len-sized allocation. The attacker chooses count and can SET_FEATURE first on a changeable user feature, so adjacent heap objects can be overwritten.
- A:HAvailability impact, high
- Overflowing the kvzalloc buffer in cxlctl_get_feature() corrupts adjacent heap metadata and oopses, and out_len==0 makes kvzalloc return ZERO_SIZE_PTR so the mailbox write through rpc_out->payload faults immediately. Either outcome is a repeatable kernel panic.