CVE-2021-45971
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 · uneditedAn issue was discovered in SdHostDriver in Insyde InsydeH2O with kernel 5.1 before 05.16.25, 5.2 before 05.26.25, 5.3 before 05.35.25, 5.4 before 05.43.25, and 5.5 before 05.51.25. A vulnerability exists in the SMM (System Management Mode) branch that registers a SWSMI handler that does not sufficiently check or validate the allocated buffer pointer (CommBufferData).
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 · moderate confidenceA vulnerability in the SdHostDriver component of Insyde InsydeH2O UEFI firmware allows a SWSMI handler in SMM (System Management Mode) to be exploited due to insufficient validation of the CommBufferData pointer before use. This enables code execution in SMM, the highest privilege level on x86 processors.
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>= 5.1, < 5.16.25>= 5.2, < 5.26.25>= 5.3, < 5.35.25>= 5.4, < 5.43.25>= 5.5, < 05.51.25CVSS 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
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/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 the UEFI firmware vendorRun 'dmidecode -s bios-vendor' or check BIOS setup information screen. This vulnerability only affects Insyde InsydeH2O UEFI firmware.Affected if The BIOS vendor is not Insyde or the firmware is not InsydeH2O
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Determine the firmware versionRun 'dmidecode -s bios-version' or check the BIOS setup information screen. Note the full version string.Affected if The firmware version falls within any of these ranges: >= 5.1 and < 5.16.25, >= 5.2 and < 5.26.25, >= 5.3 and < 5.35.25, >= 5.4 and < 5.43.25, or >= 5.5 and < 05.51.25
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Verify the kernel/bootloader versionCheck Insyde documentation or the detailed firmware revision (sometimes shown as 'Kernel version' or 'Build ID' in BIOS). Some systems display this via 'dmidecode -s bios-release-date' or by extracting the firmware ROM.Affected if The kernel version shown matches the affected version ranges in step 2 (the kernel version corresponds to the 5.x numbering in the affected ranges)
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Confirm SMM is enabledCheck if System Management Mode is active or if SWSMI (Software System Management Interrupt) handlers are registered. On Linux, tools like 'msr' tools or checking /dev/mem (with root) can reveal SMM state. The vulnerability requires SMM to be accessible.Affected if SMM is enabled and the SdHostDriver SWSMI handler is present in the firmware
You are affected if your system uses Insyde InsydeH2O UEFI firmware with a version in the affected ranges and the SdHostDriver component with SMM is present and enabled.
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 · scoped5.16.255.26.255.35.25
Apply the vendor firmware update from Insyde (kernel 5.1: 05.16.25+, 5.2: 05.26.25+, 5.3: 05.35.25+, 5.4: 05.43.25+, 5.5: 05.51.25+). This is a SMM vulnerability requiring BIOS/firmware-level remediation; no workarounds exist.
InsydeH2O firmware version 05.16.25 (for 5.1 branch), 05.26.25 (for 5.2 branch), 05.35.25 (for 5.3 branch), 05.43.25 (for 5.4 branch), or 05.51.25 (for 5.5 branch)
- 1. Identify the current InsydeH2O firmware version installed on the system (typically viewable in BIOS/UEFI setup or via system information tools)
- 2. Determine which firmware branch (5.1, 5.2, 5.3, 5.4, or 5.5) corresponds to the current installed version
- 3. Download the updated InsydeH2O firmware package from the system manufacturer's support website for the specific model
- 4. Verify the firmware file matches the appropriate fixed version: 05.16.25 or later for 5.1 branch, 05.26.25 or later for 5.2 branch, 05.35.25 or later for 5.3 branch, 05.43.25 or later for 5.4 branch, or 05.51.25 or later for 5.5 branch
- 5. Follow the manufacturer's standard firmware update process (typically via BIOS flash utility, Windows Update, or bootable USB)
- 6. Ensure the system has stable power during the firmware update process to prevent corruption
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation8.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-45971 — 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-2021-45971 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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