EDK II PXE flaw enables remote code execution before boot

The article reports a critical pre-boot remote code execution vulnerability in the TianoCore EDK II PXE driver, tracked as CVE-2026-97631. Discovered by Alex Matrosov of Anthropic and Dan Holmes-Mitra of Google, the flaw scores 9.5 on CVSS v4.0. It affects NetworkPkg in the EDK II master branch as of 14 September 2026, with no official stable release yet marked as patched in the advisory metadata.

The issue allows unauthenticated network attackers to execute arbitrary code during network boot before the operating system loads, potentially granting ring-0 access in the DXE phase and bypassing Secure Boot or measured boot verification.

The vulnerability stems from an out-of-bounds write in the PXE Base Code driver (NetworkPkg/UefiPxeBcDxe). While handling ICMP error messages during IPv4 or IPv6 network boot, the driver maintains a fixed 504-byte buffer (Mode[.]IcmpError) and copies incoming packets without correct per-fragment length checks in the PxeBcIcmpErrorDpcHandle and PxeBcIcmp6ErrorDpcHandle paths.

When a unicast ICMP error message exceeds 504 bytes, data is copied past the buffer, allowing an attacker to plant a counterfeit event so CoreSignalEvent() dispatches arbitrary code in DXE. The article notes there is no public proof-of-concept exploit and no confirmed exploitation in the wild. Mitigations include applying the patch from GitHub pull request #13302 and, for administrators, disabling PXE on untrusted networks or isolating provisioning VLANs. The advisory maintains that there is no patched official stable release and that the impact is a pre-boot remote code execution in the PXE driver.