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

Vulnerability summary

CVE-2026-29008 is a high (CVSS 8.7) Integer Underflow (Wrap or Wraparound) vulnerability in denx u-boot. EPSS estimates a 0.71% chance of exploitation in the next 30 days, higher than 52.8% of scored vulnerabilities. 2 public exploits are recorded.

Timeline

1. 08-07-2026
   PublishedVulnerability first disclosed.
2. 14-07-2026
   Last modifiedVulnerability information updated.

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.

• CWE-191Integer Underflow (Wrap or Wraparound)The product subtracts one value from another, such that the result is less than the minimum allowable integer value, which produces a value that is not equal to the correct result.