In the Linux kernel, the following vulnerability has been resolved:
ipv4: reject undersized MTUs in ip_do_fragment()
ip_do_fragment() subtracts the IPv4 header length from the effective MTU and passes the resulting payload MTU to ip_frag_next().
If the effective MTU is smaller than hlen + 8, ip_frag_next() rounds the fragment payload length down to zero. The fragmentation state then never makes forward progress: state->left, state->ptr and state->offset stay unchanged while ip_do_fragment() keeps allocating and transmitting header-only fragments until the softlockup detector fires.
This is reproducible with a route installed using "mtu lock 20", but it is also reproducible without route MTU lock, for example by forwarding a packet to a device whose MTU is 20.
Fix it in ip_do_fragment() by rejecting mtu < hlen + 8 with -EMSGSIZE, matching the existing IPv6 fragmentation check.
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Amazon Linux Ami 2 | — | Upgrade perf-debuginfoUpgrade kernel-debuginfo-common-aarch64Upgrade perfUpgrade kernel-develUpgrade kernel-livepatch-5.15.220-153.252Upgrade bpftool-debuginfoUpgrade kernel-livepatch-5.10.268-266.1092Upgrade python-perfUpgrade kernel-toolsUpgrade kernel-tools-debuginfoUpgrade kernel-debuginfoUpgrade kernel-headersUpgrade kernel-debuginfo-common-x86_64Upgrade kernel-tools-develUpgrade bpftoolUpgrade kernelUpgrade python-perf-debuginfo | Oct 19, 2026 | Oct 19, 2026 |
| Amazon_linux_2023 | — | Upgrade kernel6.18-debuginfo-common-x86_64Upgrade kernel-livepatch-6.18.48-107.148Upgrade kernel6.18-develUpgrade perf6.18Upgrade kernel6.18-tools-develUpgrade kernel6.18Upgrade kernel6.18-debuginfoUpgrade kernel6.18-modules-extraUpgrade kernel6.18-toolsUpgrade kernel6.18-modules-extra-commonUpgrade kernel6.18-debuginfo-common-aarch64Upgrade perf6.18-debuginfoUpgrade python3-perf6.18-debuginfoUpgrade python3-perf6.18Upgrade bpftool6.18-debuginfoUpgrade kernel6.18-tools-debuginfoUpgrade microvm-kernel6.18Upgrade kernel6.18-headersUpgrade bpftool6.18 | Oct 20, 2026 | Sep 4, 2026 |
| Debian | — | Upgrade linuxUpgrade linux-6.12 | Sep 21, 2026 | Sep 4, 2026 |
| Redhat_linux | — | No solution exists | Oct 19, 2026 | Sep 4, 2026 |
| Vmware Photon_os | — | Use 'tdnf update' to upgrade all packages to the latest version. | Sep 21, 2026 | Sep 4, 2026 |
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