CVE-2021-3418: Medium severity GNU GRUB2 vulnerability
If certificates that signed grub are installed into db, grub can be booted directly. It will then boot any kernel without signature validation. The booted kernel will think it was booted in secureboot mode and will implement lockdown, yet it could have been tampered. This flaw is a reintroduction of CVE-2020-15705 and only affects grub2 versions prior to 2.06 and upstream and distributions using the shimlock mechanism.
Other sources
The GRUB2 upstream version reintroduced the CVE-2020-15705. This refers to a distro specific flaw which made upstream in the mentioned version.
If certificates that signed grub are installed into db, grub can be booted directly. It will then boot any kernel without signature validation. The booted kernel will think it was booted in secureboot mode and will implement lockdown, yet it could have been tampered.
This flaw only affects upstream and distributions using the shimlock mechanism.
— Red Hat
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
redhat/grubto a version that resolves this vulnerability.Fixed in 2.06 - Upgrade
Upgrade
GRUB2 (upstream)to a version that resolves this vulnerability.Fixed in 2.06 - Compensating control
Ensure GRUB2 is not bootable without signature validation by avoiding installing certificates that signed GRUB into db (i.e., do not place GRUB-signer certificates in UEFI db).
- Operational
Reboot/verify the system boot chain after upgrading to GRUB2 2.06 to ensure the kernel is not booted without signature validation and that lockdown behavior corresponds to an untampered boot state.
Event History
Frequently Asked Questions
What is CVE-2021-3418?
CVE-2021-3418 is a vulnerability that allows grub to be booted directly without signature validation, potentially leading to tampered kernels being loaded.
What is the severity of CVE-2021-3418?
CVE-2021-3418 has a severity value of 6.4, which is considered medium.
Which software is affected by CVE-2021-3418?
Grub versions up to and excluding 2.06 are affected by CVE-2021-3418.
How can I fix CVE-2021-3418?
You can fix CVE-2021-3418 by updating Grub to version 2.06 or above.
Where can I find more information about CVE-2021-3418?
You can find more information about CVE-2021-3418 on the Red Hat Bugzilla and Red Hat Security Advisories websites.