Linux kernel lan743x driver: Use-after-free in RX checksum handling
Summary
The Microchip LAN743x Ethernet driver in the Linux kernel writes to a freed socket buffer when a received packet is split across multiple receive buffers. A remote attacker who can send suitable network traffic to an affected host may trigger a memory corruption, which can lead to a denial of service. Exploitation requires a host with a LAN743x network card, and the attack complexity is high.
Affected
- Linux kernel versions with the lan743x driver from commit cd6910501cfd9a3bdff2f5fc33c9f3cf165ca54a until the fixed stable commits
- Ubuntu 24.04 LTS and 26.04 LTS: vulnerable; Ubuntu 22.04 LTS: not affected
- Exact fixed versions per distribution: unknown from the available sources
Fixed in
- Upstream stable commits: 0e52886c4324c9897c2c62f92be3dc8316cee67e, 161a403c8625e152de03d1da22bbf9cda6dc9f9f, 5c216bfa9fb7b36804485e67975e9c98055b31ef, 6fe5c3a2503983abb431d93faeadfc7f5e6a7e33, a58024835c704419bb46d2a34e5223f65605f958, a9ce4053dc945c5372dedba5017ee675b30dc0c5
- Upstream stable kernel versions with the fix: 6.1.189, 6.6.158, 6.12.112, 6.18.54, 7.2.8 (per OSV)
- Distribution kernel packages: unknown, check the vendor advisory
Workaround
- If the LAN743x network card is not used, unload the lan743x driver or disable the interface until the kernel is patched.
- Avoid live MTU changes on hosts with this card until patched, as multi-buffer receive can occur after an MTU increase. This is a recommendation, not a vendor workaround.
Exploitation
- No evidence of active exploitation known.
- No CISA KEV entry and no public proof of concept found.
- EPSS score: 0.00435 (very low).
Our recommendation
- Check whether any host uses a Microchip LAN743x network device (for example with lspci -nn or by checking for the lan743x module).
- Install the kernel update from your distribution that includes the fix, with priority for internet-facing or edge devices.
- Until patched, avoid live MTU changes on affected hosts and unload the driver if the interface is unused.
- Monitor the vendor advisories for the exact fixed version.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Linux kernel stable commit 0e52886c4324c9897c2c62f92be3dc8316cee67e git.kernel.org
- Linux kernel stable commit a9ce4053dc945c5372dedba5017ee675b30dc0c5 git.kernel.org
- Ubuntu security notice CVE-2026-98239 ubuntu.com
- OSV entry UBUNTU-CVE-2026-98239 osv.dev
- OpenCVE CVE-2026-98239 app.opencve.io
- NVIDIA NV-Kernels pull request 657 github.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 20:51.
Original description (NVD)
In the Linux kernel, the following vulnerability has been resolved: net: lan743x: fix RX checksum use-after-free 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.
NVD references (6)
- https://git.kernel.org/stable/c/0e52886c4324c9897c2c62f92be3dc8316cee67e
- https://git.kernel.org/stable/c/161a403c8625e152de03d1da22bbf9cda6dc9f9f
- https://git.kernel.org/stable/c/5c216bfa9fb7b36804485e67975e9c98055b31ef
- https://git.kernel.org/stable/c/6fe5c3a2503983abb431d93faeadfc7f5e6a7e33
- https://git.kernel.org/stable/c/a58024835c704419bb46d2a34e5223f65605f958
- https://git.kernel.org/stable/c/a9ce4053dc945c5372dedba5017ee675b30dc0c5
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.