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CriticalVulnerabilityCVE-2026-97631updated 2 Nov 2026, 04:46 UTC

Server boot firmware flaw lets network attackers run code

A flaw in the software that starts a server before its operating system can let an attacker on the network take control of the machine. The attacker does not need a password.

Official, 4 sources
SeverityCriticalCVSS 9.5 of 10
Being exploited?UnclearNo reports either way yet
Fix available?UnclearNo fixed version published in the sources yet
How sure is this?Official, 4 sourcesBacked by an official source

How the attack works simplified

  1. 1Attacker on networkSends crafted ICMP error messages
  2. 2Server PXE bootsBoot firmware is waiting for network setup
  3. 3Buffer overflowOut-of-bounds write in PXE driver
  4. 4Code runs at bootRuns before the operating system loads
  5. ResultAttacker controls the server

What happened

A out-of-bounds write and buffer overflow in the EDK II PXE network boot driver can be triggered remotely during IPv4 or IPv6 PXE boot, leading to arbitrary code execution.

Why it is dangerous: Successful exploitation can lead to arbitrary code execution and affects confidentiality, integrity, and availability. Servers that network-boot are the most exposed, and one source says the flaw affects most servers.

Are you affected?

You are affected if your server uses EDK II UEFI firmware with PXE network boot enabled over IPv4 or IPv6, and an attacker can reach it on the network during boot.

EDK II PXE driver (exact affected versions not stated in the provided material; see advisory GHSA-99cj-7hg9-mp4m).

What to do

  1. Check the advisory GHSA-99cj-7hg9-mp4m for affected and fixed versions.
  2. Ask your server or hardware vendor for UEFI/EDK2 firmware updates that address CVE-2026-97631, and apply them.
  3. Limit untrusted network access to machines while they PXE-boot.

Timeline

  1. 22 Oct 2026, 17:17 UTC
    Publicly disclosed
  2. 22 Oct 2026, 17:17 UTC
    Reported by NVD · NVD
  3. 28 Oct 2026, 14:01 UTC
    oss-security reported on it · oss-security
  4. 28 Oct 2026, 15:46 UTC
    r/netsec reported on it · r/netsec
  5. 2 Nov 2026, 04:46 UTC
    SecurityWeek reported on it · SecurityWeek

Sources 4 reports, oldest first

Official vendor, government CERT or advisory database

  • NVD22 Oct 2026, 17:17 UTC

Security researchers research teams and mailing lists

Security press established security newsrooms

Community discussion sites, treat with care

Technical details

ID
CVE-2026-97631 · ZR-5e82c4f3
CVSS
9.5 / 10
EPSS
0.6% chance of exploitation within 30 days
Disclosed
22 Oct 2026, 17:17 UTC
On Zero Radar
before the radar started
Last change
2 Nov 2026, 04:46 UTC

The plain-language parts and the attack diagram were written by an AI model (claude-haiku-5-5) from the sources above. Facts like versions, exploitation and dates come from the sources themselves. How Zero Radar works

Server boot firmware flaw lets network attackers run code · Zero Radar