CVE-2026-29008 Details
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.
A denial-of-service vulnerability has been identified in U-Boot versions through 2026.04-rc3. The issue arises from an integer underflow in the tcp_rx_state_machine() function within the TCP handling code. A network-adjacent attacker can exploit this vulnerability by sending a malformed TCP SYN+ACK packet with a manipulated data offset. This manipulation causes the payload length to become negative, which is then incorrectly interpreted as a large unsigned integer. The erroneous payload length is passed to a memory copy function, leading to an immediate crash of the bootloader. This crash prevents the device from booting and may cause memory corruption if a specific configuration option is disabled.
Metrics
CVSS 4.0 Severity and Vector Strings:
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Jul 9, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://lists.denx.de/pipermail/u-boot/2026-May/617853.html | [email protected] | Mailing ListThird Party Advisory |
| https://u-boot.org/ | [email protected] | Product |
| https://www.vulncheck.com/advisories/u-boot-rc3-integer-underflow-dos-via-tcp-rx-state-machine | [email protected] | Third Party AdvisoryExploit |
| https://y637f9qq2x.com/posts/u-boot-tcp-nfs-vulns/ | [email protected] | Third Party AdvisoryExploit |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-191 | Integer Underflow (Wrap or Wraparound) | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| denx u-boot | < 2026.04 2026.04 rc1 2026.04 rc2 2026.04 rc3 |
CPE
Remediation
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Change History
5 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 22, 2026 | Initial Analysis | [email protected] |
| Jul 14, 2026 | CVE Modified | [email protected] |
| Jul 13, 2026 | CVE Modified | [email protected] |
| Jul 9, 2026 | CVE Modified | CISA-ADP |
| Jul 8, 2026 | New CVE Received | [email protected] |