CVE-2026-29008

Name	CVE-2026-29008
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.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
Debian Bugs	1142070

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
u-boot (PTS)	bullseye	2021.01+dfsg-5	vulnerable
	bullseye (security)	2021.01+dfsg-5+deb11u3	vulnerable
	bookworm, bookworm (security)	2023.01+dfsg-2+deb12u3	vulnerable
	trixie	2025.01-3	vulnerable
	forky, sid	2025.01-3.2	vulnerable

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
u-boot	source	(unstable)	(unfixed)			1142070

https://y637f9qq2x.com/posts/u-boot-tcp-nfs-vulns/
https://lists.denx.de/pipermail/u-boot/2026-May/617853.html