CVE-2023-40547Shim: rce in http boot support may lead to secure boot bypass

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.

Timeline

Scores

EPSS (exploitation in 30 days)

5.4% · top 7.2% of all CVEs (14 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: total

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.3.

Affected products

• Red Hat · Red Hat Enterprise Linux 7

  • unaffected 0:15.8-3.el7 – < *

• Red Hat · Red Hat Enterprise Linux 7

  • unaffected 0:15.8-1.el7 – < *

• Red Hat · Red Hat Enterprise Linux 8

  • unaffected 0:15.8-4.el8_9 – < *

• Red Hat · Red Hat Enterprise Linux 8.2 Advanced Update Support

  • unaffected 0:15.8-2.el8_2 – < *

• Red Hat · Red Hat Enterprise Linux 8.2 Telecommunications Update Service

  • unaffected 0:15.8-2.el8_2 – < *

• Red Hat · Red Hat Enterprise Linux 8.2 Update Services for SAP Solutions

  • unaffected 0:15.8-2.el8_2 – < *

• Red Hat · Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support

  • unaffected 0:15.8-2.el8_4 – < *

• Red Hat · Red Hat Enterprise Linux 8.4 Telecommunications Update Service

  • unaffected 0:15.8-2.el8_4 – < *

• Red Hat · Red Hat Enterprise Linux 8.4 Update Services for SAP Solutions

  • unaffected 0:15.8-2.el8_4 – < *

• Red Hat · Red Hat Enterprise Linux 8.6 Extended Update Support

  • unaffected 0:15.8-2.el8_6 – < *

• Red Hat · Red Hat Enterprise Linux 8.8 Extended Update Support

  • unaffected 0:15.8-2.el8 – < *

• Red Hat · Red Hat Enterprise Linux 8.8 Extended Update Support

  • unaffected 0:15.8-2.el8 – < *

• Red Hat · Red Hat Enterprise Linux 9

  • unaffected 0:15.8-4.el9_3 – < *

• Red Hat · Red Hat Enterprise Linux 9.0 Extended Update Support

  • unaffected 0:15.8-3.el9 – < *

• Red Hat · Red Hat Enterprise Linux 9.0 Extended Update Support

  • unaffected 0:15.8-2.el9 – < *

• Red Hat · Red Hat Enterprise Linux 9.0 Extended Update Support

  • unaffected 0:15.8-2.el9 – < *

• Red Hat · Red Hat Enterprise Linux 9.2 Extended Update Support

  • unaffected 0:15.8-3.el9_2 – < *

What to do

Workaround: 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.

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2023-45118 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2023-40547](https://cveledger.app/badge/CVE-2023-40547.svg)](https://cveledger.app/cve/CVE-2023-40547)

Record last updated 26 Jun 2026, 09:43 UTC.