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CVE-2026-89622
HID: mcp2221: clear rxbuf after I2C/SMBus transfer completes
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem drivers/hid. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-89622 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-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
mcp_i2c_smbus_read() stores the caller-supplied buffer pointer in mcp->rxbuf for the duration of a transfer but never clears it when the transfer finishes or times out. Once the caller frees or reuses the buffer, mcp->rxbuf becomes a dangling pointer. A delayed or spurious MCP2221_I2C_GET_DATA report can then drive mcp2221_raw_event() to memcpy device data into the freed memory, causing a write use-after-free. Route all return paths through a single exit point that clears mcp->rxbuf and mcp->rxbuf_size, so that the existing !mcp->rxbuf guard in the raw_event handler can reject any report arriving after the transfer has ended.
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/hid/hid-mcp2221.c
- What this is
- MCP2221A MICROCHIP USB-HID TO I2C BRIDGE DRIVERMAINTAINERS section matched on drivers/hid/hid-mcp2221.c · linux-i2c@vger.kernel.org · Maintained
- Kernel module
- hid_mcp2221
Check it on the machine
grep -wE 'CONFIG_HID|CONFIG_HID_MCP2221|CONFIG_HID_SUPPORT' /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.
lsmod | grep -w hid_mcp2221Prints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
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.
- bookworm, trixie, forky, sid, bookworm · linux-6.12Mnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_HID, CONFIG_HID_MCP2221, CONFIG_HID_SUPPORT
- 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
- 7.8 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
- 0.16%, higher than 5.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/hid
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.7 | 6.12.111 | d6c6b293173c |
| 5.7 | 6.18.51 | 03c34309eb1b |
| 5.7 | 7.2.4 | 968546b676d9 |
| 5.7 | 7.3 | db2333f88729 |
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
- A local attacker can bind hid-mcp2221 by forging BUS_USB 04d8:00dd via UHID_CREATE2 on /dev/uhid (no hid_is_usb() guard), then issue I2C_RDWR/I2C_SMBUS reads on the resulting /dev/i2c-N so mcp_i2c_smbus_read() leaves mcp->rxbuf dangling; a malicious USB MCP2221 is only a lower-severity physical path.
- AC:LAttack complexity, low
- The attacker controls both sides: they start the I2C/SMBus read that stores the bounce buffer in mcp->rxbuf, let mcp_i2c_smbus_read() return without clearing it (timeout or completed xfer), then inject a delayed MCP2221_I2C_GET_DATA report via UHID_INPUT so mcp2221_raw_event() memcpy's into the already-freed buffer.
- PR:LPrivileges required, low
- Neither uhid_dev_create2() nor i2cdev_open() checks capabilities; access is DAC on /dev/uhid and /dev/i2c-*, which udev uaccess-tags for the seat user and which are commonly 0660 root:i2c on embedded/industrial MCP2221 systems, i.e. low privilege rather than real init-namespace root.
- UI:NUser interaction, none
- The attacker creates the uhid device, issues the I2C/SMBus read ioctl, and injects the delayed HID input report from their own process; no separate victim action is required.
- S:UScope, unchanged
- The write use-after-free corrupts host-kernel heap or returned SMBus stack under the kernel's own authority and is ordinary local privilege-escalation/DoS, with no VM escape, IOMMU bypass, or other cross-authority impact.
- C:HConfidentiality impact, high
- mcp2221_raw_event() memcpy's attacker-controlled HID payload into a freed I2C bounce buffer (up to 60 bytes per report, repeatable up to the attacker-chosen rxbuf_size of 8192 via I2C_RDWR); a write UAF of a sprayed slab object yields an arbitrary kernel read primitive.
- I:HIntegrity impact, high
- The same memcpy is a write use-after-free of attacker-controlled bytes into freed kernel memory; with heap spraying this is an arbitrary-write and control-flow hijack primitive, so integrity impact is High per UAF guidance.
- A:HAvailability impact, high
- Writing into the freed i2c-dev bounce buffer or returned SMBus stack object can oops or panic the kernel even when not fully exploited, and the dangling mcp->rxbuf persists until the next read so the crash is retriggerable at will.