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CVE-2026-63874
net: mctp: usb: fix race between urb completion and rx_retry cancellation
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-63874 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 | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
It's possible that sequencing between setting ->stopped and cancelling the rx_retry work (in ndo_stop) could leave us with an urb queued: T1: ndo_stop T2: rx_retry_work ------------ ---------------- LD: ->stopped => false ST: ->stopped <= true usb_kill_urb() mctp_usb_rx_queue() usb_submit_urb() cancel_delayed_work_sync() That urb completion can then re-schedule rx_retry_work. Strenghen the sequencing between the stop (preventing another requeue) and the cancel by updating both atomically under a new rx lock. After setting ->rx_stopped, and cancelling pending work, we know that the requeue cannot occur, so all that's left is killing any pending urb.
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/net/mctp/mctp-usb.c
- What this is
- MANAGEMENT COMPONENT TRANSPORT PROTOCOL (MCTP)MAINTAINERS section matched on drivers/net/mctp/ · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -wE 'CONFIG_MCTP|CONFIG_MCTP_TRANSPORT_USB' /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_MCTP, CONFIG_MCTP_TRANSPORT_USB
- 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
- 2026-07-19 (3 months 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
- 0.13%, higher than 2.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.15 | 6.18.36 | 9c46f3ee1837 |
| 6.15 | 7.0.13 | d90feaa3f74b |
| 6.15 | 7.1 | 54665dce9826 |
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 race is hit in `mctp_usb_stop()` (`ndo_stop`) during netdev teardown, which is reachable via local RTNETLINK (`ip link set down`) or USB disconnect; it is not reachable from remote network input. Per the uncertainty rule, Local is chosen over Physical.
- AC:LAttack complexity, low
- An attacker can control both sides of the race by inducing RX ENOMEM to schedule `rx_retry_work` (memory pressure) and concurrently triggering netdev stop/disconnect, retrying timing until the window between `stopped=true` and `cancel_delayed_work_sync()` is won.
- PR:LPrivileges required, low
- Triggering `ndo_stop` through RTNETLINK requires `CAP_NET_ADMIN`, which is obtainable in an unprivileged user namespace; a physical USB disconnect path needs no software privileges, but PR:L is the higher-severity choice when uncertain.
- UI:NUser interaction, none
- Exploitation does not require any victim user action beyond the attacker’s own interface teardown/disconnect and memory-pressure timing.
- S:UScope, unchanged
- Impact is kernel memory corruption/UAF within the same kernel security boundary, not a cross-boundary escape such as guest-to-host or sandbox breakout.
- C:HConfidentiality impact, high
- Winning the race leaves RX URBs/completions running after `usb_free_urb()` and `free_netdev()`, producing a use-after-free on `net_device`, `urb`, and `sk_buff` objects that can be turned into arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- The post-teardown UAF on heap-allocated driver/netdev/USB objects provides exploitable write primitives (re-submitted URBs, corrupted completion handlers) suitable for control-flow hijack and privilege escalation.
- A:HAvailability impact, high
- The bug reliably causes kernel crashes (oops/panic) when freed URBs/netdevs are touched by completion handlers or rescheduled `rx_retry_work`, even before full exploitation.