CVE-2026-29008Public exploit

Bootloader crash via TCP payload length underflow

Published Jul 8, 2026 · Updated Jul 8, 2026

Integer underflow in U-Boot through 2026.04-rc3 allows remote attackers to crash the bootloader with a malformed TCP SYN+ACK reply. The TCP_SYN_SENT handler forwards a negative payload_len without tcp_seg_in_wnd() validation, and store_block() converts it into a large memcpy() length. Reachability requires network boot and attackers on the same local network able to answer the outbound SYN; the out-of-bounds read crashes startup.

CVSS severity8.7
High
EPSS probability0.71%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer underflow in U-Boot through 2026.04-rc3 allows remote attackers to crash the bootloader with a malformed TCP SYN+ACK reply. The TCP_SYN_SENT handler forwards a negative payload_len without tcp_seg_in_wnd() validation, and store_block() converts it into a large memcpy() length. Reachability requires network boot and attackers on the same local network able to answer the outbound SYN; the out-of-bounds read crashes startup.

The record

CVE
CVE-2026-29008
Published
Jul 8, 2026
Updated
Jul 8, 2026
Vendor
DENX Software Engineering GmbH
Product
U-Boot
Classifications
CWE-191, T1499.004
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=2026.04-rc3

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

DENX Software Engineering GmbH · U-Bootversion=0 <=2026.04-rc3

Published CVSS scores

7.5VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-191Integer Underflow (Wrap or Wraparound)
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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