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U BootApplication · Denx

CVE-2026-29009

CRITICAL · 9.8 CVSS v3.1 Published 2026-07-08
Fix available
A fix is available. Upgrade to 2026.04 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click 6 weeks old

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 · unedited
U-Boot before 2026.07-rc2 contains a buffer overflow vulnerability in nfs_readlink_reply() (net/nfs-common.c) when CONFIG_CMD_NFS is enabled, allowing a malicious or compromised NFS server to overflow the 2048-byte nfs_path_buff buffer by returning multiple relative symlink targets that are appended without cumulative length validation. Attackers can send two or more READLINK responses containing relative symlink targets of approximately 1100 bytes each to corrupt adjacent BSS variables including nfs_server_ip, nfs_server_mount_port, nfs_server_port, nfs_our_port, nfs_state, and rpc_id, potentially achieving memory corruption and control over the NFS client state machine.

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 confidence

U-Boot before 2026.07-rc2 has a buffer overflow in nfs_readlink_reply() (net/nfs-common.c) when CONFIG_CMD_NFS is enabled. A malicious NFS server can send multiple relative symlink targets (~1100 bytes each) that overflow the 2048-byte nfs_path_buff buffer without cumulative length validation, corrupting adjacent BSS variables including nfs_server_ip, nfs_server_port, and nfs_state, allowing control of the NFS client state machine.

MitigationUpdate U-Boot to version 2026.07-rc2 or later which includes bounds checking in nfs_readlink_reply(). Additionally, ensure only trusted NFS servers are used and consider network segmentation to limit exposure to malicious NFS servers.

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
U BootApplication
Affected:< 2026.04= 2026.04

CVSS 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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 checks

Work through these to decide whether this CVE applies to you.

  1. Confirm CONFIG_CMD_NFS is enabled in the U-Boot build
    Inspect the U-Boot configuration file (.config) or binary for the presence of CONFIG_CMD_NFS. This can be done by running 'grep CONFIG_CMD_NFS .config' in the build directory or using 'strings u-boot.bin | grep CONFIG_CMD_NFS' on the compiled binary.
    Affected if CONFIG_CMD_NFS is defined/enabled in the build configuration (the vulnerability only exists when NFS command support is compiled in)
  2. Determine if NFS client functionality is actively used
    Check if the target system uses NFS for boot, file loading, or filesystem mounting. Review boot scripts, environment variables (e.g., 'bootargs'), or device tree configuration that reference NFS mounts or the 'nfs' command.
    Affected if The system uses NFS booting, loads files from NFS shares, or otherwise invokes NFS client operations (the overflow occurs during NFS server communication)
  3. Verify network exposure to untrusted NFS servers
    Assess whether the U-Boot device can communicate with NFS servers that are not fully trusted. Check network configuration, DHCP/bootp responses, or NFS server IP settings to determine if the device may receive responses from arbitrary NFS servers.
    Affected if The device can receive NFS responses from untrusted or publicly accessible network sources (a malicious server is required to trigger the overflow)
  4. Check U-Boot version against fixed releases
    Run 'version' or 'bdinfo' in the U-Boot shell, or inspect the U-Boot binary metadata to obtain the installed version. Compare against any available security advisories or release notes addressing CVE-2026-29009.
    Affected if The installed U-Boot version predates the security fix for this vulnerability (the exact version varies by downstream maintainer)

The system is affected if CONFIG_CMD_NFS is enabled in the build, NFS client functionality is used, and the device can receive NFS responses from potentially untrusted servers.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

dbcve · scoped
Upgrade available Upgrade to 2026.04 or later
Fixed in 2026.04
Interim mitigation

Update U-Boot to version 2026.07-rc2 or later which includes bounds checking in nfs_readlink_reply(). Additionally, ensure only trusted NFS servers are used and consider network segmentation to limit exposure to malicious NFS servers.

Recommended fix Moderate confidence
  1. Disable CONFIG_CMD_NFS in the U-Boot configuration (e.g., via make menuconfig or by modifying the defconfig) to prevent the vulnerable code from being compiled and included.
  2. If NFS functionality is required, monitor the official U-Boot project resources (e.g., lists.denx.de or u-boot.org) for a security release addressing this vulnerability and upgrade to a version newer than 2026.04-rc3 once available.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in U Boot Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-29009 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data