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Alert meAnalysisCVE.org
In the Linux kernel, the following vulnerability has been resolved:
net: ipv4: Fix UDP length overflow with PMTU discover and big MTU
This commit bounds cork->base.fragsize to IP_MAX_MTU to avoid a possible overflow of UDP length that triggers a WARN in udp_set_len_short when setsockopt IP_MTU_DISCOVER is set to IP_PMTUDISC_PROBE, and a large packet is sent over a netdev with an unusually large MTU.
Steps to reproduce:
- Set device MTU bigger than IP_MAX_MTU + 20. cork->base.fragsize will
be set to that MTU in ip_setup_cork.
- Set IP_MTU_DISCOVER to IP_PMTUDISC_PROBE. It lets maxnonfragsize be
set to device MTU (cork->fragsize) in __ip_append_data, rather than to IP_MAX_MTU.
- Send 65528 bytes of payload (+8 bytes of UDP header, +20 bytes of
IPv4 header). Device MTU allows it (it's only one byte bigger than IP_MAX_MTU + IPv4 header, and the device MTU is bigger than that).
- The UDP length in the built packet is 65536, which overflows the
16-bit length field and triggers the WARN in udp_set_len_short.
Note: IP_PMTUDISC_DO with IPv4 is safe, because ip_dst_mtu_maybe_forward always clamps at IP_MAX_MTU, unlike ip6_dst_mtu_maybe_forward.
The Fixes tag points at the first commit where I could reproduce the overflow with IPv4 and IP_PMTUDISC_PROBE.
Affected VersionsENISA
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 1 package in euvd
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Attack Technique
A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.
EUVD-2026-101042
GHSA-m5wc-gf88-8h7m
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