CVE-2024-52877: Insyde InsydeH2O Buffer Overflow Flaw

CVE-2024-52877 Overview

CVE-2024-52877 is a buffer over-read vulnerability [CWE-126] in the Insyde InsydeH2O UEFI firmware. The flaw resides in the VariableRuntimeDxe driver, where the CreateVariableLockListInSmm() function uses StrSize() to determine variable name size. Improper boundary handling allows the function to read memory beyond the intended buffer. The issue affects multiple Insyde kernel branches from 5.2 through 5.7 prior to the fixed releases. Insyde published Security Advisory SA-2024016 documenting the affected versions and remediation guidance.

Critical Impact

An attacker who can influence UEFI variable data may trigger an out-of-bounds read in System Management Mode (SMM), exposing sensitive firmware memory contents.

Affected Products

• Insyde InsydeH2O kernel 5.2 before 05.29.50
• Insyde InsydeH2O kernel 5.3 before 05.38.50, kernel 5.4 before 05.46.50, kernel 5.5 before 05.54.50
• Insyde InsydeH2O kernel 5.6 before 05.61.50 and kernel 5.7 before 05.70.50

Discovery Timeline

• 2025-05-15 - CVE-2024-52877 published to NVD
• 2025-08-15 - Last updated in NVD database

Technical Details for CVE-2024-52877

Vulnerability Analysis

The vulnerability exists in the VariableRuntimeDxe driver, which manages UEFI variable services during runtime. The callback function SmmCreateVariableLockList() invokes CreateVariableLockListInSmm() inside System Management Mode. Within that handler, StrSize() is called against a variable name buffer to compute its size. Because StrSize() walks the string until it finds a null terminator, an attacker-supplied or malformed variable name without a proper terminator forces the routine to read past the allocated buffer. The resulting out-of-bounds read [CWE-126] occurs in SMM context, one of the most privileged execution environments on the platform.

Root Cause

The root cause is missing length validation before calling StrSize(). The driver trusts that the variable name buffer contains a properly null-terminated Unicode string within known bounds. When that assumption fails, StrSize() traverses adjacent memory regions until it either encounters a null word or triggers a fault. This pattern is a classic boundary handling defect in firmware code that accepts data crossing trust boundaries.

Attack Vector

The CVSS vector identifies a network-reachable attack surface with confidentiality impact only. Exploitation requires the attacker to deliver crafted UEFI variable data that reaches the vulnerable SMM handler. Successful exploitation discloses adjacent firmware memory, which may include keys, configuration data, or pointers useful for chaining further firmware attacks. There is no integrity or availability impact recorded, and no public proof-of-concept or in-the-wild exploitation has been confirmed.

No verified public exploit code is available. See the Insyde Security Advisory SA-2024016 for vendor technical details.

Detection Methods for CVE-2024-52877

Indicators of Compromise

• No public indicators of compromise have been published for CVE-2024-52877.
• Unexpected SMM faults, machine check exceptions, or firmware logs referencing VariableRuntimeDxe should be treated as suspicious.

Detection Strategies

• Inventory firmware versions across the fleet and flag systems running Insyde InsydeH2O kernel branches 5.2 through 5.7 below the fixed releases listed in SA-2024016.
• Correlate vendor firmware advisories with platform identifiers reported by management tools to identify exposed OEM devices that integrate the Insyde reference code.
• Monitor for abnormal UEFI variable write activity from operating system tooling that could be used to stage malformed variable names.

Monitoring Recommendations

• Collect SMBIOS and firmware version telemetry through endpoint management agents and forward it to a centralized data lake for version drift analysis.
• Track Insyde and OEM advisory feeds for downstream firmware updates that incorporate the SA-2024016 fix.
• Audit usage of SetVariable runtime services from userland to detect tooling capable of supplying crafted variable payloads.

How to Mitigate CVE-2024-52877

Immediate Actions Required

• Identify systems running affected Insyde InsydeH2O kernel branches and prioritize firmware updates issued by the OEM that integrates the Insyde codebase.
• Restrict administrative access to tooling capable of writing UEFI variables from the operating system.
• Enable platform firmware integrity measurement, such as TPM-backed measured boot, to detect anomalous SMM behavior.

Patch Information

Insyde has released fixed kernel versions: 5.2 at 05.29.50, 5.3 at 05.38.50, 5.4 at 05.46.50, 5.5 at 05.54.50, 5.6 at 05.61.50, and 5.7 at 05.70.50. Apply OEM-provided BIOS or UEFI updates that include these Insyde kernel revisions. Refer to the Insyde Security Pledge and Insyde Security Advisory SA-2024016 for vendor guidance.

Workarounds

• No vendor workaround replaces the firmware update; apply the OEM BIOS release that includes the fixed Insyde kernel.
• Limit local administrative privileges to reduce the population of accounts able to invoke UEFI variable write APIs.
• Where supported, enforce signed UEFI variable policies and Secure Boot to constrain attacker influence over runtime variables.

# Linux: enumerate firmware vendor and version for triage
sudo dmidecode -s bios-vendor
sudo dmidecode -s bios-version
sudo dmidecode -s bios-release-date