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

> A network-adjacent attacker can crash the U-Boot bootloader or potentially execute code by sending a malformed TCP packet that triggers an integer underflow.

- **Severity:** High 8.7 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 8 Jul 2026
- **Updated:** 14 Jul 2026
- **Also known as:** DEBIAN-CVE-2026-29008, GHSA-3qwj-q697-4ppr, UBUNTU-CVE-2026-29008

## What is CVE-2026-29008?

CVE-2026-29008 is a high-severity vulnerability in u-boot, published on 8 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2026-29008?

It affects 1 product.


Products: Denx U-Boot.

## How do I fix CVE-2026-29008?

No fix has been published for CVE-2026-29008 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-29008 being exploited?

There is no known exploitation of CVE-2026-29008 in the wild and no public exploit code.

## Other vulnerabilities in u-boot

- [CVE-2022-34835](https://insights.sbomify.com/CVE-2022-34835/): Integer overflow in n/a (critical 9.8)
- [CVE-2022-30767](https://insights.sbomify.com/CVE-2022-30767/): Memory corruption in n/a (critical 9.8)
- [CVE-2020-8432](https://insights.sbomify.com/CVE-2020-8432/): Use after free in n/a (critical 9.8)
- [CVE-2019-14192](https://insights.sbomify.com/CVE-2019-14192/): Integer overflow in n/a (critical 9.8)
- [CVE-2019-14193](https://insights.sbomify.com/CVE-2019-14193/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-29008 and fix it if it is affected.

What it is: CVE-2026-29008 is a high-severity vulnerability in u-boot, published on 8 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-29008 in the wild and no public exploit code.

Affected product: u-boot. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-29008/ (Markdown: https://insights.sbomify.com/CVE-2026-29008/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-29008
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-29008
- OSV: https://osv.dev/vulnerability/CVE-2026-29008

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-29008/
Summaries are generated and may contain mistakes; the official description above is the record.