CVE-2021-33626
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 · uneditedA vulnerability exists in SMM (System Management Mode) branch that registers a SWSMI handler that does not sufficiently check or validate the allocated buffer pointer(QWORD values for CommBuffer). This can be used by an attacker to corrupt data in SMRAM memory and even lead to arbitrary code execution.
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 confidenceA vulnerability exists in the System Management Mode (SMM) branch where a SWSMI handler fails to sufficiently validate or check allocated buffer pointers (QWORD values for CommBuffer). This insufficient input validation allows an attacker to corrupt data in SMRAM (System Management RAM) and potentially achieve arbitrary code execution at the highest CPU privilege level.
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>= 5.3, < 5.34.44>= 5.2, < 5.25.44>= 5.1, < 5.16.25>= 5.4, < 5.42.44>= 5.3, < 5.35.25>= 5.2, < 5.26.25>= 5.4, < 5.43.25all versionsall versionsall versionsall versionsall versionsall versionsall versionsCVSS 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
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/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 system firmware vendor and versionRun 'dmidecode -s bios-version' or check UEFI/BIOS setup screen for version information. For Insyde systems, note the exact version string (e.g., 5.3.x, 5.4.x).Affected if The system uses Insyde Insydeh2o firmware and the version falls within: 5.3 to <5.34.44, 5.2 to <5.25.44, 5.1 to <5.16.25, 5.4 to <5.42.44, 5.3 to <5.35.25, 5.2 to <5.26.25, or 5.4 to <5.43.25
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Check if running on a Siemens industrial deviceIdentify the device model via product labeling, boot screen, or 'dmidecode -s system-product-name'. Affected models include: Ruggedcom Apr1808, Simatic Field Pg M5/M6, Simatic Ipc127e, Ipc227g, Ipc277g, Ipc327g.Affected if The device is any of the listed Siemens models running any firmware version (all versions are affected)
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Verify SMM SWSMI handler is activeCheck UEFI/BIOS setup for 'SMM Security' or 'SWSMI' settings. On Linux, 'cat /sys/firmware/efi/systab' or check 'dmesg | grep -i smm' may indicate SMM activity. The vulnerability exists in the SWSMI handler that manages CommBuffer.Affected if The system has an active SWSMI handler processing CommBuffer (QWORD pointer validation is insufficient in the handler)
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Confirm SMRAM accessibilityCheck if SMRAM region is exposed or debuggable. On some systems, 'cat /proc/ioports' or 'cat /proc/iomem' may show SMRAM regions. Also check UEFI setup for 'Lock SMRAM' or similar security settings.Affected if SMRAM can be accessed or modified (SWSMI handler allows corrupting data in SMRAM due to insufficient pointer validation)
You are affected if you run Insyde Insydeh2o firmware at any version below the patched thresholds, or any Siemens Ruggedcom/Simatic device at any firmware version, with an active SWSMI handler managing CommBuffer in SMM.
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 · scoped5.16.255.25.445.26.25
Apply vendor-provided BIOS/UEFI firmware updates that address this SMM vulnerability. Organizations should verify their current firmware version and coordinate with system/board manufacturers for patched releases.
InsydeH2O: upgrade to 5.34.44 (for 5.3.x), 5.25.44 (for 5.2.x), 5.16.25 (for 5.1.x), or 5.42.44 (for 5.4.x); Siemens devices: contact vendor for patches
- 1. Identify the current InsydeH2O firmware version installed on the affected device by checking the UEFI BIOS setup or system information.
- 2. For InsydeH2O version 5.3.x, upgrade to version 5.34.44 or later.
- 3. For InsydeH2O version 5.2.x, upgrade to version 5.25.44 or later.
- 4. For InsydeH2O version 5.1.x, upgrade to version 5.16.25 or later.
- 5. For InsydeH2O version 5.4.x, upgrade to version 5.42.44 or later.
- 6. Obtain the firmware update from the device manufacturer (OEM) as they package InsydeH2O updates specific to their hardware.
- 7. Apply the firmware update following the OEM's recommended update procedure, which typically involves flashing the UEFI BIOS through a vendor-provided tool or recovery process.
- 8. For Siemens/Ruggedcom devices (Ruggedcom Apr1808, Simatic Field Pg M5/M6, Simatic Ipc127e, Ipc227g, Ipc277g, Ipc327g), contact Siemens Product CERT and Siemens PSIRT for specific firmware updates as the reference sources indicate no public fixed versions for these devices.
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation6.0 h
- Implementation2.0 h
- Testing12.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-33626 — 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-2021-33626 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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