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.
Metrics
CVSS 3.1 7.5/10
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HWeakness enumeration
Affected software
| Vendor | Product | Versions |
|---|---|---|
| u-boot | u-boot | <= 2026.04-rc3 |
References
- https://lists.denx.de/pipermail/u-boot/2026-May/617853.htmlMailing List, Third Party Advisory
- https://u-boot.org/Product
- https://www.vulncheck.com/advisories/u-boot-rc3-integer-underflow-dos-via-tcp-rx-state-machineThird Party Advisory, Exploit
- https://y637f9qq2x.com/posts/u-boot-tcp-nfs-vulns/Third Party Advisory, Exploit
Timeline
- Published
- Jul 8, 2026
- Last modified
- Jul 22, 2026
- NVD status
- Analyzed