CVE-2023-20521
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 · uneditedTOCTOU in the ASP Bootloader may allow an attacker with physical access to tamper with SPI ROM records after memory content verification, potentially leading to loss of confidentiality or a denial of service.
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 confidenceThis is a Time-of-Check-Time-of-Use (TOCTOU) vulnerability in the ASP Bootloader where an attacker with physical access can tamper with SPI ROM records after the bootloader has verified memory content but before that verified content is used. The race condition between verification and usage allows modification of SPI ROM contents post-verification, potentially leading to confidentiality breaches or denial of service.
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< naplespi_1.0.0.h< naplespi_1.0.0.h< naplespi_1.0.0.h< naplespi_1.0.0.h< naplespi_1.0.0.h< naplespi_1.0.0.h< naplespi_1.0.0.h< naplespi_1.0.0.hCVSS 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
- Physical
- Complexity
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:P/AC:H/PR:N/UI:N/S:U/C:H/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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Identify the exact AMD Epyc processor modelRun 'dmidecode -t processor' or check system inventory to confirm the specific CPU model (e.g., Epyc 7251, 7261, 7281, 7301, 7351, 7351p, 7371)Affected if The processor model is one of the affected Epyc 7001 series variants listed in the CVE
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Check the current firmware versionUse 'dmidecode -s bios-version' or access the BIOS/UEFI setup to retrieve the system firmware version stringAffected if The firmware version string cannot be determined or is not visible to the operating system (bootloader-level vulnerability)
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Determine the ASP Bootloader SPI ROM handling versionInspect system firmware dump or contact AMD support to identify the naplespi component version used by the ASP BootloaderAffected if The naplespi version is earlier than naplespi_1.0.0.h or cannot be verified from available system tools
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Verify if SPI ROM integrity checks occur immediately before each accessExamine bootloader configuration or firmware behavior through security assessment tools that can inspect the ASP Bootloader timing and verification logicAffected if The bootloader performs a one-time verification of SPI ROM contents rather than verifying immediately before each SPI ROM read operation
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Assess physical access controls to the systemReview physical security measures in place for the server or device hosting the affected Epyc processorAffected if Physical access to the SPI ROM is not restricted, allowing an attacker to exploit the TOCTOU window
You are affected if you run any of the listed AMD Epyc 7001 series processors (7251, 7261, 7281, 7301, 7351, 7351p, 7371) and the ASP Bootloader naplespi component version is earlier than naplespi_1.0.0.h, combined with insufficient physical access controls to the SPI ROM.
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.
dbcve · scopedImplement physical security controls to restrict access to the device; redesign the bootloader to perform cryptographic integrity verification immediately before each SPI ROM access rather than relying on a one-time verification, eliminating the TOCTOU window.
naplespi_1.0.0.h or later
- Obtain the AMD Epyc 7001 series firmware update (naplespi_1.0.0.h or later) from the official AMD support website
- Locate the specific firmware update package for your Epyc model (7251, 7261, 7281, 7301, 7351, 7351p, or 7371)
- Follow AMD's standard firmware update procedure for the Epyc processor, which typically involves using the AMD firmware update utility or BMC interface
- Reboot the system after applying the firmware update
- Verify the installed firmware version matches naplespi_1.0.0.h or later using system inventory tools
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation6.0 h
- Implementation20.0 h
- Testing12.0 h
- Review / QA6.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $12,288.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2023-20521 — 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-2023-20521 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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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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