U-Boot Out-of-Bounds Write in IP Defragmentation

Executive Summary

This vulnerability is an out-of-bounds write issue in U-Boot versions before 2026.10-rc3 when the CONFIG_IP_DEFRAG option is enabled. It occurs in the __net_defragment() function in net/net.c. Attackers can exploit it by sending a specially crafted IP fragment with a non-zero offset and the More-Fragments flag set during netboot. This corrupts adjacent memory in the bootloader, potentially causing crashes.

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Detection Guidance

This vulnerability affects U-Boot versions before 2026.10-rc3 with CONFIG_IP_DEFRAG enabled. Detection requires checking the U-Boot version and configuration. Use 'strings' or 'grep' on the U-Boot binary to verify CONFIG_IP_DEFRAG is enabled. Monitor network traffic for fragmented IP packets with non-zero offset and More-Fragments flag during netboot.

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Impact Analysis

If exploited, this vulnerability could allow remote attackers to crash the U-Boot bootloader during system startup. This may prevent the device from booting properly, leading to denial of service. Systems relying on U-Boot for netboot operations are particularly at risk if they use vulnerable versions.

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Compliance Impact

This vulnerability could potentially impact compliance with GDPR or HIPAA if exploited in systems handling sensitive data during boot processes. A crash in the bootloader may disrupt secure boot mechanisms or data integrity checks required by these regulations.

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Mitigation Strategies

Upgrade U-Boot to version 2026.10-rc3 or later. Disable CONFIG_IP_DEFRAG in U-Boot configuration if upgrading is not possible. Restrict network access to U-Boot netboot services to trusted sources only. Monitor for crashes during netboot operations.

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