CVE-2021-27138

Secure-boot bypass via ambiguous FIT node lookup

Published Feb 17, 2021 · Updated Nov 3, 2025

Secure-boot bypass in Das U-Boot before 2021.04-rc2 allows attackers to load an unintended FIT image through a crafted node name. libfdt treats a node's unit-address suffix as optional during lookup, so a reference such as kernel can resolve to a different kernel@1 node. Exploitation requires a crafted FIT to reach local boot processing and user interaction, after which signature checks can apply to the wrong image.

CVSS severity7.8
High
EPSS probability1.10%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Secure-boot bypass in Das U-Boot before 2021.04-rc2 allows attackers to load an unintended FIT image through a crafted node name. libfdt treats a node's unit-address suffix as optional during lookup, so a reference such as kernel can resolve to a different kernel@1 node. Exploitation requires a crafted FIT to reach local boot processing and user interaction, after which signature checks can apply to the wrong image.

The record

CVE
CVE-2021-27138
Published
Feb 17, 2021
Updated
Nov 3, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1553.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 17, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.8MITRECVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P

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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1553.002Subvert Trust Controls: Code Signing

Public exploit references

No public exploit references are available in this record.

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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