#uefi
27 posts · Last used Sep 26
Fix Secure Boot FOREVER with Mosby
RE: https://infosec.exchange/@ESETresearch/116917582564392811
Thank you @ESETresearch@infosec.exchange for working with us to responsibly disclose this UEFI vulnerability.
Read the corresponding CERT/CC vul note
Interested in doing more #UEFI vulnerability discovery work? Check out the cert-uefi-parser on GitHub and PyPI.
#ESETresearch discovered and reported to @certcc@infosec.exchange 11 old Microsoft-signed UEFI shim bootloaders that allow bypassing UEFI Secure Boot on most UEFI systems. Read about it at https://www.welivesecurity.com/en/eset-research/forgotten-uefi-shims-undermining-secure-boot/
Tracked by #CVE-2026-8863 and #CVE-2026-10797, all these vulnerable shims were revoked in Microsoft’s June Patch Tuesday updates.
https://www.cve.org/CVERecord?id=CVE-2026-8863
https://www.cve.org/CVERecord?id=CVE-2026-10797
Exploiting these vulnerable shims allows execution of untrusted code at system boot by using the Bring Your Own Vulnerable Driver (#BYOVD) technique, enabling deployment of malicious UEFI bootkits on systems that trust the Microsoft Corporation UEFI CA 2011 certificate.
What makes these old shims dangerous is not a novel vulnerability, it’s that no new vulnerability is needed to bypass Secure Boot. Just an old, still-trusted, unrevoked shim and basic knowledge of how UEFI works is enough to bypass UEFI Secure Boot and deploy a UEFI bootkit.
For more details and instructions on how to verify that the dbx patches were properly applied on your system, read our blogpost:
https://www.welivesecurity.com/en/eset-research/forgotten-uefi-shims-undermining-secure-boot/
Reminder: Bleibt entspannt bezüglich der ablaufenden Zertifikate für #UEFI #SecureBoot, eure bestehenden #Linux-Installationen sollten alle weiterhin booten.
Vereinfacht gesagt stört sich nämlich kaum eine Firmware daran, wenn der Boot-Loader eine Signatur eines mittlerweile abgelaufenen Zertifikats trägt – anders als ein Webbrowser, der in so einem Fall den Besuch einer Webseite blockiert.
Im Detail gibt es naturgemäß doch einige Tücken, die euch über kurz oder lang ereilen könnten. Siehe dazu folgende Texte:
- https://fedoramagazine.org/expiration-of-microsoft-secure-boot-keys/
- https://wiki.debian.org/SecureBoot/CAChanges
- https://www.redhat.com/en/blog/expiration-secure-boot-signing-certificates-2026
- https://discourse.ubuntu.com/t/microsoft-uefi-ca-rotation-what-it-means-for-ubuntu-users-and-vendors/82652
- https://mjg59.dreamwidth.org/72892.html







