Critical security flaw found in server firmware

A critical security vulnerability, labeled CVE-2026-97631, has been identified in the network boot function of most UEFI firmwares used in servers. This function, known as PXE, is part of the EDK II open-source codebase managed by the TianoCore project, which is widely used by firmware publishers like AMI, Insyde, and Phoenix, including Microsoft's hardened version called Project Mu.

Vulnerability involves memory overflow

The vulnerability stems from a memory overflow issue in the PXE driver, specifically in components called NetworkPkg or UefiPxeBcDxe. During the network boot process, the PXE driver receives error messages via ICMP. It copies these messages into a fixed-size memory space of 504 bytes, but continues copying even if the message is longer, leading to a potential overflow.

High risk with specific conditions

The vulnerability has a CVSS 4.0 score of 9.5, indicating a very high risk. However, exploitation requires specific conditions: the use of PXE booting, which is common in servers but not in general consumer devices, and knowledge of the exact firmware version being targeted. Once these conditions are met, an attacker can inject commands without needing authentication.

Discovery and patching timeline

The flaw was discovered by Alex Matrosov from Anthropic and Dan Holmes-Mitra from Google, who also provided a recommended fix. The TianoCore team reserved the CVE identifier on September 24. However, an error in the disclosure process occurred when AMI published a public pull request in late September that described the vulnerability and included the patch.

Impact and response from vendors

The patch was proposed, but the parties involved had agreed to delay public details until January to allow firmware publishers time to release updates. AMI's early disclosure accelerated this timeline. Now, companies like Dell, Lenovo, SuperMicro, and HPE must release updates, which may require server downtime. Intel and Arm stated their products are not affected, but others like AMD, Microsoft, and Amazon have not confirmed their status.

Mitigation and recommendations

Users are advised to inventory their PXE-enabled machines and disable the feature if not needed. If PXE is essential, it should be confined to an isolated network segment. Monitoring manufacturer support pages and filtering unexpected ICMP messages are also recommended to reduce the risk of exploitation.