CVE-2026-80793
Received Received - Intake

Fragmentation Failure in Linux Kernel

Publication date: 2026-09-04

Last updated on: 2026-09-04

Assigner: kernel.org

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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Meta Information

Published
2026-09-04
Last Modified
2026-09-04
Generated
2026-09-04
AI Q&A
2026-09-04
EPSS Evaluated
N/A
NVD
CVE-2026-80793
EUVD
EUVD-2026-71436

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel occurs in the IPv4 fragmentation process. When the effective MTU is smaller than the IPv4 header length plus 8 bytes, the fragmentation logic fails to progress. This causes the system to repeatedly send empty fragments, leading to a softlockup where the kernel becomes unresponsive.

Detection Guidance

This vulnerability is specific to the Linux kernel's IPv4 fragmentation logic and may not have direct detection commands. Monitor for softlockups or excessive fragmentation attempts in kernel logs. Check for routes with unusually small MTUs using commands like 'ip route' or 'route -n'.

Impact Analysis

This vulnerability can cause system hangs or crashes due to softlockups, disrupting network services and potentially leading to denial-of-service conditions. Systems performing IPv4 packet fragmentation may become unresponsive.

Mitigation Strategies

Apply the Linux kernel patch that fixes this issue. Avoid using routes with MTUs smaller than the header length plus 8 bytes. Monitor system logs for fragmentation-related errors or softlockups.

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