CVE-2026-29008
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedU-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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceU-Boot contains an integer underflow in the TCP receive state machine where a malformed TCP SYN+ACK packet with a manipulated data offset causes payload_len to become negative. The TCP_SYN_SENT handler bypasses the tcp_seg_in_wnd() validation check, allowing the negative value to be implicitly converted to a large unsigned integer (e.g., 0xFFFFFFD8) and passed to memcpy() in store_block(), triggering a crash and potential memory corruption.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 2026.04= 2026.04CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check U-Boot versionRun the 'version' command in the U-Boot prompt or examine the U-Boot binary/boot logs to identify the exact version string (e.g., 2026.04-rc3, 2026.01, etc.)Affected if The installed version is 2026.04-rc3 or any earlier version (e.g., 2026.01, 2025.x, etc.)
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Verify TCP support is compiled inCheck the U-Boot build configuration or binary for CONFIG_NET_TCP or CONFIG_CMD_NET symbols; in U-Boot, run 'bdinfo' or inspect the compiled defconfig file to see if TCP networking is enabledAffected if CONFIG_NET_TCP or TCP networking support is defined in the build configuration, meaning the vulnerable TCP code path is present in the binary
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Confirm TCP functionality is in useCheck U-Boot environment variables (printenv) or boot scripts for network-related configurations such as ipaddr, serverip, or netboot commands that utilize TCPAffected if TCP-based network operations (e.g., TFTP over TCP, network boot using TCP) are configured or expected to be used in the environment
A user is affected if their U-Boot version is 2026.04-rc3 or earlier AND TCP support is compiled into the build AND the device uses TCP networking functionality, allowing a malformed SYN+ACK packet to trigger the memcpy overflow.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor data2026.04
Implement bounds checking in tcp_rx_user_data() to validate payload_len before use in memcpy(), and ensure tcp_seg_in_wnd() is invoked in the TCP_SYN_SENT handler to reject out-of-window packets.
- Consultation3.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,408.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-29008 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-29008 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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