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CVE-2023-40550

Publication date 23 January 2024

Last updated 24 July 2024

Ubuntu priority

Medium

Why this priority?

Cvss 3 Severity Score

5.5 · Medium

Score breakdown

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.]

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

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")

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 5.5 · Medium
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