CVE-2026-29008
U-Boot 2026.04-rc3 Integer Underflow DoS via tcp_rx_state_machine()
HIGH 8.7EPSS 0.7%
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
- u-boot
- CVSS v4.0 VULNCHECK
- 8.7 HIGH
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - CVSS v3.1 VULNCHECK
- 7.5 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - EPSS
- 0.71% chance of exploitation in the next 30 days, 53rd percentile
- Published
- 2026-07-08
- Updated
- 2026-07-14
Proof-of-concept exploits (1)
Security advisories
- https://lists.denx.de/pipermail/u-boot/2026-May/617853.html
- https://www.vulncheck.com/advisories/u-boot-rc3-integer-underflow-dos-via-tcp-rx-state-ma…
- https://y637f9qq2x.com/posts/u-boot-tcp-nfs-vulns
- https://u-boot.org