CVE-2026-20753: Slim Bootloader Privilege Escalation

CVE-2026-20753 Overview

CVE-2026-20753 is an integer overflow vulnerability [CWE-190] in the Unified Extensible Firmware Interface (UEFI) firmware for the Intel Slim Bootloader. The flaw enables a privileged local attacker to trigger local code execution and escalate privileges within the firmware boundary. Successful exploitation impacts confidentiality, integrity, and availability of the affected system, with cascading impact to subsequent system components. The issue is tracked under Intel Security Advisory SA-01425 and requires local access combined with elevated privileges to exploit.

Critical Impact
An authenticated local attacker with high privileges can trigger an integer overflow in the Slim Bootloader UEFI firmware to achieve local code execution at the firmware level, undermining platform trust below the operating system.

Affected Products

Intel Slim Bootloader UEFI firmware (refer to Intel Security Advisory SA-01425 for affected versions)
Platforms shipping Slim Bootloader as the boot firmware component
Downstream OEM firmware builds derived from vulnerable Slim Bootloader releases

Discovery Timeline

2026-05-12 - CVE-2026-20753 published to NVD
2026-05-13 - Last updated in NVD database

Technical Details for CVE-2026-20753

Vulnerability Analysis

The vulnerability resides in the UEFI firmware for the Intel Slim Bootloader, an open-source boot firmware used on Intel platforms. An integer overflow condition occurs during firmware processing, allowing an attacker with high privileges on the local system to corrupt firmware-level state. Because the defect executes in the pre-boot or firmware execution environment, code execution gained here operates below the operating system boundary. This undermines protections such as Secure Boot, kernel integrity, and OS-level access controls. The flaw is locally exploitable with low attack complexity and requires no user interaction, but it does require existing privileged access on the target system. EPSS data indicates a low near-term probability of opportunistic exploitation, consistent with the local privileged precondition.

Root Cause

The root cause is an integer overflow [CWE-190] in the Slim Bootloader UEFI firmware. Arithmetic on attacker-influenced values wraps past the representable range of the integer type. The overflowed result is then used in downstream operations, such as length calculations or buffer sizing, leading to memory corruption and a path to firmware-level code execution.

Attack Vector

An adversary with high privileges and local access supplies crafted inputs to the firmware interface that performs the vulnerable arithmetic. The overflow propagates through subsequent firmware logic, enabling escalation of privilege within the firmware execution context. No user interaction is required, and attack complexity is low when the prerequisite privileged access is present. Refer to the Intel Security Advisory SA-01425 for vendor-supplied technical details.

// No verified proof-of-concept is publicly available.
// The vulnerability manifests as an integer overflow in Slim Bootloader
// firmware arithmetic. See Intel Security Advisory SA-01425 for details.

Detection Methods for CVE-2026-20753

Indicators of Compromise

No public indicators of compromise have been published for CVE-2026-20753 at the time of this writing.
Unexpected firmware version mismatches between platform inventory and OEM-published builds may warrant investigation.
Boot integrity measurement deviations recorded by TPM PCR values can indicate firmware tampering.

Detection Strategies

Inventory firmware versions across the fleet and compare against fixed releases identified in Intel Security Advisory SA-01425.
Monitor for privileged process activity that interacts with firmware update interfaces or UEFI runtime services.
Correlate local privilege escalation events with subsequent firmware update or boot configuration changes.

Monitoring Recommendations

Enable and centrally collect platform measured-boot logs and TPM event logs for anomaly review.
Track administrative access on systems running Slim Bootloader-derived firmware, since exploitation requires privileged local access.
Alert on unauthorized firmware flashing operations or changes to boot configuration data.

How to Mitigate CVE-2026-20753

Immediate Actions Required

Identify systems and OEM platforms that incorporate Intel Slim Bootloader firmware and prioritize them for patching.
Apply the firmware updates referenced in Intel Security Advisory SA-01425 as soon as OEM builds are available.
Restrict and audit local administrative access, since exploitation requires high privileges on the target system.

Patch Information

Intel has published guidance and fixed firmware information in Intel Security Advisory SA-01425. Platform owners should obtain updated Slim Bootloader builds from the relevant OEM or platform vendor, since downstream firmware images must be rebuilt against the patched upstream source.

Workarounds

Enforce least privilege so that only essential accounts hold the administrative rights required to reach the vulnerable firmware interface.
Enable platform protections such as Secure Boot, BIOS write protection, and TPM-based measured boot to raise the cost of firmware tampering.
Where supported, require signed firmware updates and disable unauthenticated firmware flashing paths until a patched build is deployed.

bash

# Example: verify current firmware/BIOS version on Linux to compare against fixed releases
sudo dmidecode -s bios-version
sudo dmidecode -s bios-release-date
sudo dmidecode -s bios-vendor