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
| Author | Note |
|---|---|
| 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
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 |
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 |
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 |