CVE-2026-80793
Description
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.
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Affected products
1Patches
Vulnerability mechanics
References
9- git.kernel.org/stable/c/3556beb8ca86677af2aca5bfbed6f8e790fccc83nvd
- git.kernel.org/stable/c/36e0741833bd823866f8cb9f112f37cea1a70b60nvd
- git.kernel.org/stable/c/515b6816ba0c12d8415c88e5f41e6ec029e35cfanvd
- git.kernel.org/stable/c/74ce7389f8f562d39015f59a00ef7ad6acd37803nvd
- git.kernel.org/stable/c/a716a64a4ba68cd46f2745fba2b1099fe8e0aa59nvd
- git.kernel.org/stable/c/b0ea911453ce7210e8200a07a94d2458bd1e6430nvd
- git.kernel.org/stable/c/c0726f0caf8c6b3208552949e17d23634a2f3129nvd
- git.kernel.org/stable/c/c8a74adccaf028223054633b532593101dfcc581nvd
- git.kernel.org/stable/c/d9d1a676b033acabf8e5645f730486d1f8204a3fnvd
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