CVE-2021-21572 Overview
CVE-2021-21572 is a buffer overflow vulnerability in the Dell BIOSConnect feature, a pre-boot component used to recover or update the operating system over the network directly from BIOS. An authenticated administrator with local access can exploit the flaw to execute arbitrary code in the pre-boot environment and bypass UEFI restrictions. Because the vulnerability sits below the operating system, successful exploitation can undermine Secure Boot, firmware integrity, and OS-level security controls. The issue affects a broad set of Dell client platforms, including Latitude, Precision, OptiPlex, Inspiron, Vostro, XPS, Alienware, and G-series systems.
Critical Impact
Arbitrary code execution in the BIOS pre-boot environment, enabling UEFI restriction bypass and persistent firmware-level compromise on more than 100 Dell client models.
Affected Products
- Dell Latitude, Precision, OptiPlex, and XPS firmware (multiple models)
- Dell Inspiron, Vostro, G-series, and Alienware firmware (multiple models)
- Dell ChengMing 3990 and 3991 firmware
Discovery Timeline
- 2021-06-24 - CVE-2021-21572 published to NVD
- 2024-11-21 - Last updated in NVD database
Technical Details for CVE-2021-21572
Vulnerability Analysis
The vulnerability resides in Dell BIOSConnect, a feature that allows BIOS to reach Dell back-end services to recover or update firmware and the operating system. BIOSConnect runs in the UEFI pre-boot environment, before operating system security controls are loaded. A buffer overflow condition in BIOSConnect allows an authenticated administrator with local access to corrupt memory used by the firmware. The flaw maps to [CWE-122] heap-based buffer overflow and [CWE-787] out-of-bounds write. Because the affected code executes in System Management Mode and UEFI context, successful exploitation grants the attacker control beneath the operating system kernel.
Root Cause
The BIOSConnect code does not properly validate the size of attacker-influenced input before copying it into a fixed-size buffer. The resulting out-of-bounds write corrupts adjacent firmware memory structures. Attackers can leverage the corruption to alter execution flow within the UEFI runtime, bypassing the protections enforced by Secure Boot and signed firmware policies.
Attack Vector
Exploitation requires local access and administrator-level privileges on the target Dell system. The attacker triggers BIOSConnect operations and supplies oversized or malformed data that reaches the vulnerable copy routine. Once memory is corrupted, the attacker can pivot from operating system administrator to firmware-level execution. This crosses a trust boundary, escalating from a compromised OS to persistent control of the platform across reinstalls. No public proof-of-concept is listed in the enriched data and the CVE is not present on the CISA KEV list.
Detection Methods for CVE-2021-21572
Indicators of Compromise
- Unexpected BIOS or UEFI firmware version changes outside of approved maintenance windows.
- Unauthorized BIOSConnect activity, including unsanctioned firmware recovery or OS recovery attempts initiated from BIOS.
- Discrepancies between measured boot values reported by TPM event logs and the expected baseline.
Detection Strategies
- Compare firmware versions across the fleet to a known-good baseline and alert on deviations on Dell client models listed in the advisory.
- Monitor administrative actions that touch firmware update utilities, BIOS configuration tools, or Dell Command | Update.
- Use endpoint telemetry to correlate local administrator logons with subsequent reboot events and firmware modifications.
Monitoring Recommendations
- Ingest Windows Event Logs, Dell management agent logs, and TPM measured boot data into a centralized analytics platform.
- Track changes to UEFI variables and Secure Boot policy state on endpoints running affected Dell firmware.
- Flag any attempt to disable Secure Boot, modify boot order, or run unsigned pre-boot binaries.
How to Mitigate CVE-2021-21572
Immediate Actions Required
- Apply the BIOS updates published in the Dell Security Advisory DSA-2021-106 for every affected model.
- Restrict local administrator privileges on Dell endpoints to reduce the population of users who can trigger the vulnerable code path.
- Validate Secure Boot is enabled and enforced on all affected Dell systems after patching.
Patch Information
Dell released fixed BIOS versions for the affected platforms. Refer to the Dell Security Advisory for the minimum fixed BIOS version per model. Deploy the updates through Dell Command | Update, Dell Client Management Pack, or your standard firmware deployment tooling.
Workarounds
- Disable the BIOSConnect feature in BIOS setup until firmware updates are applied across the fleet.
- Disable the HTTPS Boot feature in BIOS configuration on affected platforms as an interim control.
- Enforce a BIOS administrator password to prevent unauthorized modification of pre-boot settings.
# Configuration example - disable BIOSConnect via Dell Command | Configure (cctk)
cctk.exe --BIOSConnect=Disabled
cctk.exe --HttpsBoot=Disabled
cctk.exe --SetupPwd=<strong-password>
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
