CVE-2021-33627

An issue was discovered in Insyde InsydeH2O Kernel 5.0 before 05.09.11, 5.1 before 05.17.11, 5.2 before 05.27.11, 5.3 before 05.36.11, 5.4 before 05.44.11, and 5.5 before 05.52.11 affecting FwBlockServiceSmm. Software SMI services that use the Communicate() function of the EFI_SMM_COMMUNICATION_PROTOCOL do not check whether the address of the buffer is valid, which allows use of SMRAM, MMIO, or OS kernel addresses.

Published: 2022-02-02 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-33627 is rated Moderate Risk (41.3/100): CVSS High severity, with low exploitation likelihood (EPSS 0.32%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-33627

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.15% 0.32% +0.17%
2 2026-02-08 0.15% 0.15% -0.01%
3 2025-11-21 — 0.15% —

Full EPSS history (16 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-33627

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.2 3.1 HIGH
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:H)
They need powerful rights—admin, root, or similar—before this pays off.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.5 6.0 [email protected]
7.2 2.0 HIGH
AV:L/AC:L/Au:N/C:C/I:C/A:C Click to expand
Access vector (AV:L)
Requires local access to the target system.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:C)
Complete confidentiality impact.
Integrity impact (I:C)
Complete integrity impact.
Availability impact (A:C)
Complete availability impact.
 3.9 10.0 [email protected]

Weakness enumeration for CVE-2021-33627

Affected software / configurations for CVE-2021-33627

Vendor Product Version Raw CPE
insyde insydeh2o >= 5.0, < 5.08.29 cpe:2.3:a:insyde:insydeh2o:*:*:*:*:*:*:*:*
insyde insydeh2o >= 5.1, < 5.16.29 cpe:2.3:a:insyde:insydeh2o:*:*:*:*:*:*:*:*
insyde insydeh2o >= 5.2, < 5.26.29 cpe:2.3:a:insyde:insydeh2o:*:*:*:*:*:*:*:*
insyde insydeh2o >= 5.3, < 5.35.29 cpe:2.3:a:insyde:insydeh2o:*:*:*:*:*:*:*:*
siemens simatic_field_pg_m5_firmware — cpe:2.3:o:siemens:simatic_field_pg_m5_firmware:*:*:*:*:*:*:*:*
siemens simatic_field_pg_m6_firmware — cpe:2.3:o:siemens:simatic_field_pg_m6_firmware:*:*:*:*:*:*:*:*
siemens simatic_ipc127e_firmware — cpe:2.3:o:siemens:simatic_ipc127e_firmware:*:*:*:*:*:*:*:*
siemens simatic_ipc227g_firmware — cpe:2.3:o:siemens:simatic_ipc227g_firmware:*:*:*:*:*:*:*:*
siemens simatic_ipc277g_firmware — cpe:2.3:o:siemens:simatic_ipc277g_firmware:*:*:*:*:*:*:*:*
siemens simatic_ipc327g_firmware — cpe:2.3:o:siemens:simatic_ipc327g_firmware:*:*:*:*:*:*:*:*
siemens simatic_ipc377g_firmware — cpe:2.3:o:siemens:simatic_ipc377g_firmware:*:*:*:*:*:*:*:*
siemens simatic_ipc427e_firmware — cpe:2.3:o:siemens:simatic_ipc427e_firmware:*:*:*:*:*:*:*:*
siemens simatic_ipc477e_firmware — cpe:2.3:o:siemens:simatic_ipc477e_firmware:*:*:*:*:*:*:*:*
siemens simatic_ipc627e_firmware — cpe:2.3:o:siemens:simatic_ipc627e_firmware:*:*:*:*:*:*:*:*
siemens simatic_ipc647e_firmware — cpe:2.3:o:siemens:simatic_ipc647e_firmware:*:*:*:*:*:*:*:*
siemens simatic_ipc677e_firmware — cpe:2.3:o:siemens:simatic_ipc677e_firmware:*:*:*:*:*:*:*:*
siemens simatic_ipc847e_firmware — cpe:2.3:o:siemens:simatic_ipc847e_firmware:*:*:*:*:*:*:*:*
siemens simatic_itp1000_firmware — cpe:2.3:o:siemens:simatic_itp1000_firmware:*:*:*:*:*:*:*:*

References for CVE-2021-33627

cvelogic Threat Intelligence