Integer overflow in Denx U-Boot
CVE-2026-29008
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.007 (51.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 52nd percentile — 51.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.007 · newest: 0.007 · change: 0.000
Affected products
- Denx U-Boot — versions 2026.04
- U-Boot — versions 0
Weakness classification (CWE)
References
- lists.denx.de/pipermail/u-boot/2026-May/617853.html (issue-tracking, Mailing List, Third Party Advisory)
- u-boot.org/ (Product, product)
- www.vulncheck.com/advisories/u-boot-rc3-integer-underflow-dos-via-tcp-rx-state-… (Exploit, Third Party Advisory, third-party-advisory)
- y637f9qq2x.com/posts/u-boot-tcp-nfs-vulns/ (Exploit, technical-description, Third Party Advisory, exploit)
Frequently asked questions
- What is CVE-2026-29008?
- CVE-2026-29008 is a high-severity vulnerability in Denx U-Boot, classified under Integer Underflow. CVSS score: 7.5/10. Published 2026-07-08.
- How severe is CVE-2026-29008?
- High severity. CVSS v3 base score is 7.5 out of 10.