dbcve.org
Insydeh2oApplication · Insyde

CVE-2020-5956

HIGH · 7.5 CVSS v3.1 Published 2022-01-05
Fix available
A fix is available. Upgrade to 05.15.11 / 5.25.11 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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 · unedited
An issue was discovered in SdLegacySmm in Insyde InsydeH2O with kernel 5.1 before 05.15.11, 5.2 before 05.25.11, 5.3 before 05.34.11, and 5.4 before 05.42.11. The software SMI handler allows untrusted external input because it does not verify CommBuffer.

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 confidence

A vulnerability exists in the SdLegacySmm SMI handler within Insyde InsydeH2O UEFI firmware. The handler fails to validate the Communication Buffer (CommBuffer) before processing input, allowing untrusted external input to be accepted. This affects kernel 5.1 versions before 05.15.11, 5.2 before 05.25.11, 5.3 before 05.34.11, and 5.4 before 05.42.11. As an SMM vulnerability, it operates at the highest privilege level on the system.

MitigationApply the vendor-supplied firmware update corresponding to the kernel version (05.15.11, 05.25.11, 05.34.11, or 05.42.11) to patch the CommBuffer validation issue in the SdLegacySmm handler.

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
Insydeh2oApplication
Affected:>= 5.2, < 5.25.11>= 5.1, < 05.15.11>= 5.3, < 05.34.11>= 5.4, < 05.42.11

CVSS 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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify the firmware vendor
    Use system tools to retrieve UEFI/BIOS vendor information. On Linux, run 'dmidecode -s bios-vendor' or check /sys/class/dmi/id/bios_vendor. On Windows, run 'wmic bios get Manufacturer' or check System Information.
    Affected if The vendor is not Insyde (or InsydeH2O is not used), as this CVE specifically affects Insyde InsydeH2O firmware.
  2. Retrieve the Insyde kernel version
    On Linux, run 'dmidecode -s bios-version' to get the firmware version string, which contains the kernel version (e.g., 05.10, 05.20, 05.30). On Windows, run 'wmic bios get Version'. The version format typically shows the kernel as the first two digits (05.xx).
    Affected if The version string cannot be retrieved or does not match Insyde's version format.
  3. Compare against affected version ranges
    Parse the retrieved kernel version from step 2 and compare to: Kernel 5.1: < 05.15.11; Kernel 5.2: >= 5.2, < 05.25.11; Kernel 5.3: >= 5.3, < 05.34.11; Kernel 5.4: >= 5.4, < 05.42.11. Determine which kernel branch (5.1, 5.2, 5.3, or 5.4) your version belongs to by examining the major version number.
    Affected if The installed version falls within any of the vulnerable ranges (e.g., 05.10.11, 05.20.20, 05.31.05, or 05.40.20 would all be affected).
  4. Confirm the SdLegacySmm handler presence (optional)
    This is a static analysis of the firmware image. Extract the UEFI firmware (if tools like uefi-firmware-parser are available) and search for the SdLegacySmm module or SMI handler. This step typically requires advanced firmware analysis tools and is not practical for most defenders.
    Affected if The SdLegacySmm handler is present in the firmware image, which is the case for all systems using the affected InsydeH2O versions.

A system is affected if it runs Insyde InsydeH2O UEFI firmware with a kernel version in any of the vulnerable ranges (5.1 < 05.15.11, 5.2 < 05.25.11, 5.3 < 05.34.11, or 5.4 < 05.42.11), as the unvalidated CommBuffer in the SdLegacySmm SMI handler can be exploited.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 05.15.11 / 5.25.11 / 05.34.11 or later
Fixed in 05.15.115.25.1105.34.11
Interim mitigation

Apply the vendor-supplied firmware update corresponding to the kernel version (05.15.11, 05.25.11, 05.34.11, or 05.42.11) to patch the CommBuffer validation issue in the SdLegacySmm handler.

Recommended fix High confidence

InsydeH2O kernel 5.1 to 05.15.11+; kernel 5.2 to 05.25.11+; kernel 5.3 to 05.34.11+; kernel 5.4 to 05.42.11+

  1. Identify the current InsydeH2O kernel version installed on the affected system
  2. Obtain the appropriate firmware update from the system vendor (OEM) that includes the fixed InsydeH2O version
  3. For kernel 5.1.x: upgrade to version 05.15.11 or later
  4. For kernel 5.2.x: upgrade to version 05.25.11 or later
  5. For kernel 5.3.x: upgrade to version 05.34.11 or later
  6. For kernel 5.4.x: upgrade to version 05.42.11 or later
  7. Apply the firmware update following the OEM's recommended procedure, which typically involves flashing the UEFI firmware via vendor-provided tools or BIOS update utilities
  8. Verify the updated firmware version matches the target fixed version after applying the update
Caveat UEFI firmware updates carry inherent risk and should be performed carefully following vendor instructions; improper flashing can render the system unbootable

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Insydeh2o Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing4.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,900
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,040.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2020-5956 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-5956 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

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.

What belongs here
  • 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