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CVE-2020-27749

Published: 2 March 2021

A flaw was found in grub2 in versions prior to 2.06. Variable names present are expanded in the supplied command line into their corresponding variable contents, using a 1kB stack buffer for temporary storage, without sufficient bounds checking. If the function is called with a command line that references a variable with a sufficiently large payload, it is possible to overflow the stack buffer, corrupt the stack frame and control execution which could also circumvent Secure Boot protections. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.

From the Ubuntu Security Team

Chris Coulson discovered that a buffer overflow existed in the command line parser in GRUB 2. A local attacker could use this to execute arbitrary code and bypass UEFI Secure Boot restrictions.

Notes

AuthorNote
sbeattie
grub2-unsigned will contain fixes and supersede grub2, which will contain only BIOS grub bits.

Priority

Medium

Cvss 3 Severity Score

7.5

Score breakdown

Status

Package Release Status
grub2-unsigned
Launchpad, Ubuntu, Debian
xenial Pending
(2.04-1ubuntu42)
bionic
Released (2.04-1ubuntu44.1.2)
focal
Released (2.04-1ubuntu44.2)
groovy
Released (2.04-1ubuntu44.2)
upstream Needs triage

trusty Does not exist

hirsute
Released (2.04-1ubuntu42)
jammy Not vulnerable
(2.06-2ubuntu7)
kinetic Not vulnerable
(2.06-2ubuntu12)
lunar Not vulnerable
(2.06-2ubuntu16)
impish
Released (2.04-1ubuntu45)
grub2-signed
Launchpad, Ubuntu, Debian
upstream Needs triage

trusty Needed

hirsute
Released (1.164)
bionic
Released (1.167~18.04.5)
focal
Released (1.167.2)
groovy
Released (1.167.2)
jammy Not vulnerable
(1.180)
xenial Pending
(1.164)
kinetic Not vulnerable
(1.185)
lunar Not vulnerable
(1.192)
impish
Released (1.169)
grub2
Launchpad, Ubuntu, Debian
trusty Needed

xenial Needed

bionic Needed

focal Needed

jammy Not vulnerable
(2.06-2ubuntu7)
kinetic Not vulnerable
(2.06-2ubuntu12)
lunar Not vulnerable
(2.06-2ubuntu16)
upstream Needs triage

Severity score breakdown

Parameter Value
Base score 7.5
Attack vector Local
Attack complexity High
Privileges required High
User interaction None
Scope Changed
Confidentiality High
Integrity impact High
Availability impact High
Vector CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H