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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
bionic
Released (2.04-1ubuntu44.1.2)
focal
Released (2.04-1ubuntu44.2)
groovy
Released (2.04-1ubuntu44.2)
trusty Does not exist

upstream Needs triage

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)
mantic Not vulnerable
(2.06-2ubuntu17)
xenial
Released (2.04-1ubuntu42)
grub2-signed
Launchpad, Ubuntu, Debian
trusty Needed

upstream Needs triage

bionic
Released (1.167~18.04.5)
focal
Released (1.167.2)
groovy
Released (1.167.2)
hirsute
Released (1.164)
jammy Not vulnerable
(1.180)
kinetic Not vulnerable
(1.185)
lunar Not vulnerable
(1.192)
impish
Released (1.169)
mantic Not vulnerable
(1.193)
xenial
Released (1.164)
grub2
Launchpad, Ubuntu, Debian
upstream Needs triage

bionic Not vulnerable
(does not affect Secure Boot)
focal Not vulnerable
(does not affect Secure Boot)
jammy Not vulnerable
(does not affect Secure Boot)
kinetic Not vulnerable
(does not affect Secure Boot)
lunar Not vulnerable
(does not affect Secure Boot)
mantic Not vulnerable
(does not affect Secure Boot)
trusty Not vulnerable
(does not affect Secure Boot)
xenial Not vulnerable
(does not affect Secure Boot)

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