CVE-2026-19398 in FA507NV
Summary
by MITRE • 08/27/2026
“unsupported-when-assigned.” An out-of-bounds write in the SmiFlash SMM module of ASUS FA507NU and FA507NV BIOS allows a local administrator to cause a system crash (BSOD) or BIOS corruption via a crafted software SMI (SW SMI) request with an oversized length value.Refer to the ' Security Update for ASUS FA507NV / FA507NU BIOS ' section on the ASUS Security Advisory for more information.
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Analysis
by VulDB Data Team • 08/27/2026
The vulnerability identified as unsupported-when-assigned represents a critical out-of-bounds write flaw located within the System Management Mode (SMM) module of SmiFlash, specifically affecting ASUS FA507NU and FA507NV BIOS implementations. This defect arises from insufficient validation of input parameters during the processing of software-generated system management interrupts, commonly referred to as SW SMIs. When a local administrator issues a crafted request containing an oversized length value, the underlying code fails to perform adequate boundary checks before writing data to memory buffers allocated within the SMM environment. Because System Management Mode operates at a higher privilege level than standard operating systems and has direct access to physical memory and hardware registers, this out-of-bounds write can overwrite critical system structures or firmware variables that are essential for stable boot processes and runtime operations.
From an operational perspective, the immediate impact of exploiting this vulnerability is severe system instability leading to a Blue Screen of Death (BSOD) due to kernel-level corruption triggered by the SMM handler executing invalid memory writes. More critically, if the overwritten data includes firmware configuration variables or critical bootloader components stored in non-volatile storage accessible via the BIOS interface, it can result in permanent BIOS corruption. This type of damage may render the system unbootable, requiring specialized hardware tools to reflash the SPI flash chip manually, thereby causing significant downtime and potential loss of sensitive data if backups are not available. The vulnerability allows a local administrator to escalate their impact from standard user privileges to compromising the entire firmware integrity layer, which is typically considered a trusted boundary in modern computing architectures.
This flaw aligns with Common Weakness Enumeration (CWE) categories such as CWE-787: Out-of-bounds Write and CWE-120: Buffer Overflow, reflecting the fundamental failure to validate array indices or buffer lengths before memory operations. In terms of tactical classification under the MITRE ATT&CK framework, this vulnerability facilitates privilege escalation through local access, potentially enabling an attacker to bypass security controls enforced by UEFI Secure Boot if the firmware state is compromised. The attack vector involves crafting a specific SW SMI request, which requires knowledge of the internal interfaces exposed by the SmiFlash module, indicating that while it targets administrative privileges, it relies on precise exploitation techniques rather than broad network-based attacks.
Mitigation strategies primarily involve applying the official security update provided by ASUS for the FA507NV and FA507NU BIOS models as detailed in their specific Security Advisory. Administrators should ensure that firmware is updated to versions where input validation logic has been strengthened to reject oversized length values during SW SMI processing. Additionally, implementing strict access controls on physical ports and restricting local administrative privileges can reduce the attack surface for such exploits. For environments where immediate patching is not feasible, monitoring system logs for unusual SMM activity or unexpected reboots may provide early detection indicators, although prevention through firmware updates remains the most effective defense against this class of out-of-bounds write vulnerabilities in BIOS modules.