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CVE-2023-40551

Published: 23 January 2024

A flaw was found in the MZ binary format in Shim. An out-of-bounds read may occur, leading to a crash or possible exposure of sensitive data during the system's boot phase.

From the Ubuntu Security Team

[pe-relocate: Fix bounds check for MZ binaries In read_header(), we attempt to parse the PE binary headers. In doing so, if there is an MZ (i.e. MS-DOS) header, we locate the PE header by finding the offset in that header. Unfortunately that is not correctly bounds checked, and carefully chosen values can cause an out-of-bounds ready beyond the end of the loaded binary. Unfortunately the trivial fix (bounds check that value) also makes it clear that the way we were determining if an image is loadable on this platform and distinguishing between PE32 and PE32+ binaries has the exact same issue going on, and so the fix includes reworking that logic to correctly bounds check all of those tests as well. 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
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)

Priority

Medium

Cvss 3 Severity Score

5.1

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/5a5147d1e19cf90ec280990c84061ac3f67ea1ab
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 5.1
Attack vector Local
Attack complexity Low
Privileges required High
User interaction None
Scope Unchanged
Confidentiality Low
Integrity impact None
Availability impact High
Vector CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H