CVE-2023-40547

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Important Important Impact What does this mean?
8.3 CVSS v3 Base Score

Description

A remote code execution vulnerability was found in Shim. The Shim boot support trusts attacker-controlled values when parsing an HTTP response. This flaw allows an attacker to craft a specific malicious HTTP request, leading to a completely controlled out-of-bounds write primitive and complete system compromise. This flaw is only exploitable during the early boot phase, an attacker needs to perform a Man-in-the-Middle or compromise the boot server to be able to exploit this vulnerability successfully.

Statement

This flaw is only exploitable when the machine is booting UEFI through the network. During startup, before loading a local boot image, Shim checks whether the system is configured to support network booting. If the check succeeds, Shim attempts to load the bootable image from the boot's previously configured server using the HTTP protocol, which exposes the system to the vulnerability described by this CVE.

Mitigation

If a system isn’t required to boot from the network, configure the server’s boot order to disable entirely or skip the network boot.

Additional Information

External References

Content from www.cve.org is not included.https://www.cve.org/CVERecord?id=CVE-2023-40547

Content from nvd.nist.gov is not included.https://nvd.nist.gov/vuln/detail/CVE-2023-40547

Affected Packages and Issued Red Hat Security Errata

Products / Services Components State Errata
Red Hat Enterprise Linux 7 shim Fixed RHSA-2024:1959
Red Hat Enterprise Linux 7 shim-signed Fixed RHSA-2024:1959
Red Hat Enterprise Linux 8 shim Fixed RHSA-2024:1902
Red Hat Enterprise Linux 8.2 Advanced Update Support shim Fixed RHSA-2024:1834
Red Hat Enterprise Linux 8.2 Telecommunications Update Service shim Fixed RHSA-2024:1834
Red Hat Enterprise Linux 8.2 Update Services for SAP Solutions shim Fixed RHSA-2024:1834
Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support shim Fixed RHSA-2024:1873
Red Hat Enterprise Linux 8.4 Telecommunications Update Service shim Fixed RHSA-2024:1873
Red Hat Enterprise Linux 8.4 Update Services for SAP Solutions shim Fixed RHSA-2024:1873
Red Hat Enterprise Linux 8.6 Extended Update Support shim Fixed RHSA-2024:2086
Unless explicitly stated as not affected, all previous versions of packages in any minor update stream of a product listed here should be assumed vulnerable, although may not have been subject to full analysis.

Common Vulnerability Scoring System (CVSS) Score Details

Important note

CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authorities (CNA) source for its products and services (see Red Hat classifications ).

CVSS v3 Score Breakdown Red Hat NVD
CVSS v3 Base Score 8.3 8.3
Attack Vector Adjacent Network Adjacent Network
Attack Complexity High High
Privileges Required None None
User Interaction None None
Scope Changed Changed
Confidentiality Impact High High
Integrity Impact High High
Availability Impact High High

CVSS v3 Vector

Red Hat CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

NVD CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Red Hat CVSS v3 Score Explanation

In our view, the Attack Vector is more accurately "Adjacent", as an attacker would need a way to intercept and interject traffic between a target system and a legitimate boot server; this traffic is typically restricted to local networks or networks protected by other means, such as virtual private networks. For that same reason, we consider the attack complexity "High". The attacker must already possess a means of intercepting legitimate boot-related network traffic, a situation that could itself be exploited in many other ways. Finally, regarding scope, while the flaw does not directly compromise neighboring components such as disk encryption, the potential for misdirecting users to harvest credentials or other information exists, as does the potential to use this flaw as one in a chain, with the intent to persist a compromise across boots.

Acknowledgements

Red Hat would like to thank Bill Demirkapi (Microsoft Security Response Center) for reporting this issue.

Frequently Asked Questions

Why is Red Hat's CVSS v3 score or Impact different from other vendors?

 For open source software shipped by multiple vendors, the CVSS base scores may vary for each vendor's version depending on the version they ship, how they ship it, the platform, and even how the software is compiled. This makes scoring of vulnerabilities difficult for third-party vulnerability databases such as NVD that only provide a single CVSS base score for each vulnerability. Red Hat scores reflect how a vulnerability affects our products specifically.

For more information, see https://access.redhat.com/solutions/762393.

My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?
  • "Under investigation" doesn't necessarily mean that the product is affected by this vulnerability. It only means that our Analysis Team is still working on determining whether the product is affected and how it is affected.
  • "Affected" means that our Analysis Team has determined that this product is affected by this vulnerability and might release a fix to address this in the near future.

What can I do if my product is listed as "Will not fix"?

 A "will not fix" status means that a fix for an affected product version is not planned or not possible due to complexity, which may create additional risk.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Upgrade to a supported product version that includes a fix for this vulnerability (recommended).
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.

What can I do if my product is listed as "Fix deferred"?

 A deferred status means that a fix for an affected product version is not guaranteed due to higher-priority development work.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.
  • Red Hat Engineering focuses on addressing high-priority issues based on their complexity or limited lifecycle support. Therefore, lower-priority issues will not receive immediate fixes.

What is a mitigation?

 A mitigation is an action that can be taken to reduce the impact of a security vulnerability, without deploying any fixes.

I have a Red Hat product but it is not in the above list, is it affected?

 The listed products were found to include one or more of the components that this vulnerability affects. These products underwent a thorough evaluation to determine their affectedness by this vulnerability. Note that layered products (such as container-based offerings) that consume affected components from any of the products listed in this table may be affected and are not represented.

Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?

 In order to maintain code stability and compatibility, Red Hat usually does not rebase packages to entirely new versions. Instead, we backport fixes and new features to an older version of the package we distribute. This can result in some security scanners that only consider the package version to report the package as vulnerable. To avoid this, we suggest that you use an approved vulnerability scanner from our This content is not included.Red Hat Vulnerability Scanner Certification program.