CVE-2026-29008: Denx U-Boot

High severity, CVSS 7.5. EPSS: 0.7% chance of exploitation in the next 30 days.

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.

Affected products

• Denx U-Boot: before 2026.04 (fixed in 2026.04); version 2026.04 only

Published 2026-07-08. Last modified 2026-07-22.