CVE-2021-21556
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 · uneditedDell PowerEdge R640, R740, R740XD, R840, R940, R940xa, MX740c, MX840c, and T640 Server BIOS contain a stack-based buffer overflow vulnerability in systems with NVDIMM-N installed. A local malicious user with high privileges may potentially exploit this vulnerability, leading to a denial of Service, arbitrary code execution, or information disclosure in UEFI or BIOS Preboot Environment.
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 confidenceStack-based buffer overflow vulnerability in Dell PowerEdge BIOS (R640, R740, R740XD, R840, R940, R940xa, MX740c, MX840c, T640) specifically triggered when NVDIMM-N memory modules are installed. Local high-privileged attacker can exploit this to execute arbitrary code, cause DoS, or disclose information within the UEFI/BIOS Preboot Environment.
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< 2.11.2< 2.11.2< 2.11.2< 2.11.2< 2.11.2< 2.11.2< 2.11.2< 2.11.2CVSS 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
- Local
- Complexity
- Low
- Privileges
- High
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:H/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 checksWork through these to decide whether this CVE applies to you.
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Identify your PowerEdge server modelUse iDRAC web interface, iDRAC command line (racadm), or check the system service tag label on the chassis to confirm the exact model (R640, R740, R740xd, R840, R940, R940xa, T640, MX740c, or MX840c)Affected if The server model is one of the affected models listed in the CVE (R640, R740, R740xd, R840, R940, R940xa, T640, MX740c, MX840c)
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Check the installed BIOS/firmware versionAccess iDRAC web interface under Firmware Inventory, or run 'racadm get BIOS.BiosBootSettings' via iDRAC command line, or view firmware version displayed during POST or in BIOS setup under Firmware RevisionAffected if The firmware version is lower than 2.11.2 (for example, 2.8.0, 2.10.1, etc.)
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Verify if NVDIMM-N memory modules are installedCheck physical DIMM slots for NVDIMM-N modules (look for NVDIMM-N branded modules), or query via iDRAC under Memory Inventory, or run 'racadm get Memory' to list all memory devices and their typesAffected if NVDIMM-N modules are physically present in the server (the vulnerability only triggers when these specific NVDIMM-N modules are installed)
You are affected if your server is one of the listed PowerEdge models, has NVDIMM-N memory installed, and runs BIOS firmware version below 2.11.2; all three conditions must be true.
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 data2.11.2
Apply Dell-provided BIOS/firmware updates for affected PowerEdge models. Organizations should identify systems with NVDIMM-N installed and prioritize patching, as this is a firmware-level vulnerability requiring BIOS update rather than software patching.
- Consultation2.0 h
- Implementation4.0 h
- Testing4.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-21556 — 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-2021-21556 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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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.
- 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