CVE-2026-43057 net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback
A flaw in Linux kernel networking causes incorrect handling of tunneled IPv6 traffic, potentially leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-43057?
CVE-2026-43057 is a high-severity denial of service vulnerability in Linux kernel, published on 1 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback
NETIF_F_IPV6_CSUM only advertises support for checksum offload of packets without IPv6 extension headers. Packets with extension headers must fall back onto software checksumming. Since TSO depends on checksum offload, those must revert to GSO.
The below commit introduces that fallback. It always checks network header length. For tunneled packets, the inner header length must be checked instead. Extend the check accordingly.
A special case is tunneled packets without inner IP protocol. Such as RFC 6951 SCTP in UDP. Those are not standard IPv6 followed by transport header either, so also must revert to the software GSO path.
Which versions are affected by CVE-2026-43057?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-43057?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-43057 being exploited?
There is no known exploitation of CVE-2026-43057 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-43057, DEBIAN-CVE-2026-43057, GHSA-rfm2-xxcf-h65g, ROOT-OS-UBUNTU-2404-CVE-2026-43057, UBUNTU-CVE-2026-43057.