Vulnerability · Published Jul 8, 2026 · Assigned by VulnCheck

CVE-2026-29008U-Boot 2026.04-rc3 Integer Underflow DoS via tcp_rx_state_machine()

High 7.5

In plain English

A high-severity security flaw in u-boot from u-boot. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 54% of all known vulnerabilities).

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.7%top 46.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	u-boot	no fix listed	DEBIAN-CVE-2026-29008
Debian:13	u-boot	no fix listed	DEBIAN-CVE-2026-29008
Debian:14	u-boot	no fix listed	DEBIAN-CVE-2026-29008
Ubuntu:22.04:LTS	u-boot	no fix listed	UBUNTU-CVE-2026-29008
Ubuntu:24.04:LTS	u-boot	no fix listed	UBUNTU-CVE-2026-29008
Ubuntu:25.10	u-boot	no fix listed	UBUNTU-CVE-2026-29008
Ubuntu:26.04:LTS	u-boot	no fix listed	UBUNTU-CVE-2026-29008
Ubuntu:26.10	u-boot	no fix listed	UBUNTU-CVE-2026-29008
Ubuntu:22.04:LTS	u-boot-nezha	no fix listed	UBUNTU-CVE-2026-29008
Ubuntu:24.04:LTS	u-boot-nezha	no fix listed	UBUNTU-CVE-2026-29008

Affected products (as reported)

Vendor	Product	Versions
u-boot	u-boot	0 – through 2026.04-rc3

Weakness: CWE-191 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://y637f9qq2x.com/posts/u-boot-tcp-nfs-vulns/ technical-description, exploit
Mailing List Outreach issue-tracking
Project Webpage product
https://www.vulncheck.com/advisories/u-boot-rc3-integer-underflow-dos-via-tcp-rx-state-machine third-party-advisory