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CVE-2026-98239
net: lan743x: fix RX checksum use-after-free
Published 2026-10-06 (13 days ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-98239 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 | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6568-1 · 2026-10-16 · text | 6.12.113-1 | Update the kernel and reboot. DSA-6568-1 shipped the fix on 2026-10-16, in 6.12.113-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.8-1 | Update the kernel and reboot. Fixed in 7.2.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.8-1 | Update the kernel and reboot. Fixed in 7.2.8-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
lan743x_rx_process_buffer() adds each non-first receive buffer to the head skb's frag_list. On the last descriptor, lan743x_rx_trim_skb() linearizes the head and frees the fragment skb metadata. The checksum-success path then writes ip_summed through the local skb pointer, which still points to the final fragment. This causes a use-after-free write when a packet spans more than one receive buffer. Set ip_summed on the surviving head skb instead. Multi-buffer receive can occur after a live MTU increase because existing ring entries keep their old buffer size until they are replenished. A KUnit test invoking lan743x_rx_process_buffer() with a two-buffer packet produced a one-byte KASAN use-after-free write before this change. The same test passed after the change. The driver object also builds with W=1. This was not tested on physical LAN743x hardware.
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/ethernet/microchip/lan743x_main.c
- What this is
- MICROCHIP LAN743X ETHERNET DRIVERMAINTAINERS section matched on drivers/net/ethernet/microchip/lan743x_* · netdev@vger.kernel.org · Maintained
- Kernel module
- lan743x
Check it on the machine
grep -wE 'CONFIG_ETHERNET|CONFIG_LAN743X|CONFIG_NET_VENDOR_MICROCHIP' /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 lan743xPrints 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.
- bookwormMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- trixieMnot built on amd64/cloud-amd64, arm64/cloud-arm64, armel/rpi
- forky, sidMnot 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_ETHERNET, CONFIG_LAN743X, CONFIG_NET_VENDOR_MICROCHIP
- 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
- 2026-10-06 (13 days ago)source
- CVSS
- 8.1 high
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.47%, higher than 39.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- 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 |
|---|---|---|
| 6.1 | 6.1.189 | 0e52886c4324 |
| 6.1 | 6.6.158 | a58024835c70 |
| 6.1 | 6.12.112 | 6fe5c3a25039 |
| 6.1 | 6.18.54 | 5c216bfa9fb7 |
| 6.1 | 7.2.8 | 161a403c8625 |
| 6.1 | 7.3 | a9ce4053dc94 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DSA-6568-1 | 2026-10-16 | trixie 6.12.113-1 | 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:NAttack vector, network
- The UAF write runs in lan743x_rx_process_buffer() (NAPI RX) while it handles an ordinary received Ethernet/IP frame from a remote sender. The sender's frame must be larger than the pre-change buffer size so the chip spreads it across several ring descriptors, which a routed jumbo-MTU path can deliver.
- AC:HAttack complexity, high
- Buffers are sized mtu+ETH_HLEN+FCS+2 and the MAC caps frames at mtu+18 (MAC_RX_FSE_), so multi-buffer frames only occur after an admin raises the MTU on a live interface, while stale ring entries remain, or through the chip's occasional extra-buffer quirk. The remote attacker cannot produce either condition.
- PR:NPrivileges required, none
- The trigger is a received frame with a valid checksum handled in the NAPI poll path, lan743x_rx_napi_poll -> lan743x_rx_process_buffer. The sender needs no authentication or credentials on the host.
- UI:NUser interaction, none
- Once the ring holds stale smaller buffers, no user on the victim needs to do anything; sending the oversized frame triggers the stale write. The admin's MTU change is already counted in AC:H.
- S:UScope, unchanged
- The freed sk_buff and the corrupted slab memory are inside the kernel itself; no VM, IOMMU or sandbox boundary is crossed.
- C:HConfidentiality impact, high
- After skb_linearize() in lan743x_rx_trim_skb() frees the frag_list skb, its skbuff_head_cache slot can be reused by another skb. The stale write then hits a live object the attacker can steer with packet timing, which counts as a use-after-free per the scoring guidance.
- I:HIntegrity impact, high
- skb->ip_summed = CHECKSUM_UNNECESSARY is written into a freed sk_buff. If the slot has been reallocated, this corrupts another live skb and can make the stack accept forged or corrupted packets without checking their checksums. It is heap memory corruption.
- A:HAvailability impact, high
- Writing into a freed and possibly reused sk_buff from the RX softirq can corrupt slab state and oops or panic the kernel; KASAN flagged the write in the author's KUnit reproducer.