CVE-2026-29008

High

Description

U-Boot through 2026.04-rc3 contains an integer underflow vulnerability in the tcp_rx_state_machine() function (net/tcp.c) that allows a network-adjacent attacker to crash the bootloader by sending a malformed TCP SYN+ACK packet with a manipulated data offset field causing payload_len to become negative. When the TCP_SYN_SENT handler calls tcp_rx_user_data() without invoking tcp_seg_in_wnd() validation, the negative payload_len is implicitly converted to a large unsigned integer (e.g., 0xFFFFFFD8) and passed to memcpy() in store_block(), causing an immediate crash that prevents device boot and may enable memory corruption when CONFIG_LMB is disabled.

SeverityHigh

CVSS7.5

Exploit probability—

ProductDenx U-boot

PublishedJul 8, 2026

First seenJul 8, 2026

Weakness typeCWE-191CWE-191

How to fix

Update

denx u-boot2026.04 or later

Affected products

Product	Affected versions	Fixed in
denx u-boot	v < 2026.04, 2026.04	2026.04

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