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CVE-2026-80995
net: mctp: hold a reference to the route device in mctp_route_lookup()
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem net/mctp. Debian urgency: unimportant.
Debian does not build this code. The per-release build detail is under "Where it lives" below.
What to do, per Debian release
Debian's own status for CVE-2026-80995 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
mctp_route_lookup() uses rt->dev without holding a reference on it. mctp_route_lookup_single() returns the route under RCU only, so the route's device can be torn down concurrently: mctp_dev_put() drops the last reference and synchronously kfree()s mdev->addrs. mctp_dev_saddr() then reads rt->dev->addrs[0], giving a use-after-free reachable by an unprivileged local AF_MCTP user on the receive/forwarding path (no CAP_NET_RAW required): BUG: KASAN: slab-use-after-free in mctp_route_lookup Read of size 1 at addr ... by task mctp_uaf/... mctp_route_lookup mctp_pkttype_receive Freed by task ...: kfree mctp_dev_put mctp_dev_notify In the same window mctp_dst_from_route() -> mctp_dev_hold() also increments a refcount that has already reached zero ("refcount_t: addition on 0 ... mctp_dev_hold"). This reintroduces the use-after-free class of CVE-2023-3439: the source address lookup was moved ahead of the point where the destination takes its device reference. Take a reference with refcount_inc_not_zero() before touching rt->dev, skip a device that is already dead, and drop the reference once the destination has taken its own.
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.
net/mctp/route.c
- What this is
- MANAGEMENT COMPONENT TRANSPORT PROTOCOL (MCTP)MAINTAINERS section matched on net/mctp/ · netdev@vger.kernel.org · Maintained
- Kernel module
- none to look for. The file would have gone into mctp, and Debian does not compile it into that module, so finding mctp in lsmod would say nothing about this CVE.
Check it on the machine
grep -w CONFIG_MCTP /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 4 releases below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.
- bookworm, trixie, forky, sidn
- n
- not enabled on any flavour - this release does not build the code
- Build switch
- CONFIG_MCTP
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 5.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- net/mctp
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 7.1 | 7.2.4 | cc561f8af255 |
| 7.1 | 7.3 | 408da1df1811 |
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 UAF is reached when mctp_pkttype_receive() calls mctp_route_lookup() while the route device is destroyed via mctp_dev_notify()/NETDEV_UNREGISTER. An unprivileged local user can create a TUN (ARPHRD_NONE auto-attaches mctp_dev), inject ETH_P_MCTP frames, and delete that netdev; this is a local syscall/netlink path, not a remote IP service.
- AC:LAttack complexity, low
- The attacker controls both sides of the race by injecting MCTP packets on one thread and unregistering the TUN/MCTP netdev on another, and can retry until mctp_dev_saddr() runs after mctp_dev_put() has synchronously kfree'd mdev->addrs.
- PR:LPrivileges required, low
- TUN creation, MCTP address/route setup, and netdev teardown require CAP_NET_ADMIN, which an unprivileged user obtains in a user+net namespace. The receive/forwarding path has no CAP_NET_RAW check, unlike mctp_sendmsg().
- UI:NUser interaction, none
- Exploitation requires no victim action; the attacker alone creates the interface, injects frames, and tears it down.
- S:UScope, unchanged
- Impact is in-kernel use-after-free and local privilege escalation within the same kernel security authority; no VM escape, IOMMU bypass, or sandbox boundary is crossed.
- C:HConfidentiality impact, high
- This is a use-after-free of mdev->addrs (and a dangling mctp_dev after refcount-add-on-0); UAF of a kmalloc object enables heap reuse and arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- After the last reference is dropped, mctp_dst_from_route() still calls mctp_dev_hold() and later dst.output() uses the freed device; reclaiming that object yields an arbitrary write and control-flow hijack primitive.
- A:HAvailability impact, high
- KASAN reports a slab-use-after-free in mctp_route_lookup and a refcount_t addition-on-0 in mctp_dev_hold; the UAF reliably oopses or panics the kernel even when not fully exploited.