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CVE-2023-40551

Publication date 23 January 2024

Last updated 24 July 2024

Ubuntu priority

Medium

Why this priority?

Cvss 3 Severity Score

5.1 · Medium

Score breakdown

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.]

Read the notes from the security team

Status

Package Ubuntu Release Status
secureboot-db 24.10 oracular
Not affected
24.04 LTS noble
Not affected
23.10 mantic
Not affected
23.04 lunar Ignored end of life, was needs-triage
22.04 LTS jammy
Not affected
20.04 LTS focal
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty
Not affected
shim 24.10 oracular
Fixed 15.8-0ubuntu1
24.04 LTS noble
Fixed 15.8-0ubuntu1
23.10 mantic Ignored end of life, was needed
23.04 lunar Ignored end of life, was needs-triage
22.04 LTS jammy
Vulnerable
20.04 LTS focal
Vulnerable
18.04 LTS bionic
Needs evaluation
16.04 LTS xenial Ignored install media keys will never be revoked
14.04 LTS trusty Ignored install media keys will never be revoked
shim-signed 24.10 oracular
Fixed 1.58
24.04 LTS noble
Fixed 1.58
23.10 mantic Ignored end of life, was needed
23.04 lunar Ignored end of life, was needs-triage
22.04 LTS jammy
Vulnerable
20.04 LTS focal
Vulnerable
18.04 LTS bionic
Needs evaluation
16.04 LTS xenial Ignored install media keys will never be revoked
14.04 LTS trusty Ignored install media keys will never be revoked

Notes

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)

Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package Patch details
shim

Severity score breakdown

Parameter Value
Base score 5.1 · Medium
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