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CVE-2023-40550

Published: 23 January 2024

An out-of-bounds read flaw was found in Shim when it tried to validate the SBAT information. This issue may expose sensitive data during the system's boot phase.

From the Ubuntu Security Team

[Fix an out-of-bound read in verify_buffer_sbat() In verify_buffer_sbat(), we have a goal-seeking loop to find the .sbat section header. Unfortunately, while the actual contents of the section are checked for being inside the binary, no such check exists for the contents of the section table entry. As a result, a carefully constructed binary will cause an out-of-bounds read checking if the section name is ".sbat\0\0\0" or not. This patch adds a check that each section table entry is within the bounds of the binary. It's not currently known if this is actually exploitable beyond creating a denial of service, and an attacker who is in a position to use it for a denial of service attack must already be able to do so.]

Notes

AuthorNote
eslerm
UEFI Security Response Team states that dbx update is not needed
eslerm
secureboot-db should only ever be updated after shim secureboot-db is not updated on ESM releases as doing so would revoke install media keys Note that key revocation is required to protect against evil housekeeper attacks (such as BlackLotus) see also e7f5fdf ("pe-relocate: Ensure nothing else implements CVE-2023-40550")

Priority

Medium

Cvss 3 Severity Score

5.5

Score breakdown

Status

Package Release Status
secureboot-db
Launchpad, Ubuntu, Debian
bionic Not vulnerable
(sbat only update)
focal Not vulnerable
(sbat only update)
jammy Not vulnerable
(sbat only update)
lunar Ignored
(end of life, was needs-triage)
mantic Not vulnerable
(sbat only update)
noble Not vulnerable
(sbat only update)
trusty Not vulnerable
(sbat only update)
upstream Not vulnerable
(sbat only update)
xenial Not vulnerable
(sbat only update)
shim
Launchpad, Ubuntu, Debian
bionic Needs triage

focal Needed

jammy Needed

lunar Ignored
(end of life, was needs-triage)
mantic Ignored
(end of life, was needed)
noble
Released (15.8-0ubuntu1)
trusty Ignored
(install media keys will never be revoked)
upstream Needs triage

xenial Ignored
(install media keys will never be revoked)
Patches:
upstream: https://github.com/rhboot/shim/commit/93ce2552f3e9f71f888a672913bfc0eef255c56d
shim-signed
Launchpad, Ubuntu, Debian
bionic Needs triage

focal Needed

jammy Needed

lunar Ignored
(end of life, was needs-triage)
mantic Ignored
(end of life, was needed)
noble
Released (15.8)
trusty Ignored
(install media keys will never be revoked)
upstream Needs triage

xenial Ignored
(install media keys will never be revoked)

Severity score breakdown

Parameter Value
Base score 5.5
Attack vector Local
Attack complexity Low
Privileges required Low
User interaction None
Scope Unchanged
Confidentiality High
Integrity impact None
Availability impact None
Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N