CVE-2023-40547

A remote code execution vulnerability was found in Shim. The Shim boot support trusts attacker-controlled values when parsing an HTTP response. This flaw allows an attacker to craft a specific malicious HTTP request, leading to a completely controlled out-of-bounds write primitive and complete system compromise. This flaw is only exploitable during the early boot phase, an attacker needs to perform a Man-in-the-Middle or compromise the boot server to be able to exploit this vulnerability successfully.

This flaw is only exploitable when the machine is booting UEFI through the network. During startup, before loading a local boot image, Shim checks whether the system is configured to support network booting. If the check succeeds, Shim attempts to load the bootable image from the boot's previously configured server using the HTTP protocol, which exposes the system to the vulnerability described by this CVE.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

If a system isn’t required to boot from the network, configure the server’s boot order to disable entirely or skip the network boot.