CVE-2023-40546: Shim: out-of-bounds read printing error messages

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-01-29 · updated 2026-06-17
Weakness: CWE-476

Description

A flaw was found in Shim when an error happened while creating a new ESL variable. If Shim fails to create the new variable, it tries to print an error message to the user; however, the number of parameters used by the logging function doesn't match the format string used by it, leading to a crash under certain circumstances.

Affected products

Fedoraproject Fedora: 39
Red Hat Enterprise Linux: 8.0, 9.0
Red Hat Bootloader Team shim: before 15.8 — fixed in 15.8

How to fix

Upgrade to a fixed version: Red Hat Bootloader Team shim 15.8. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2023-40546 or the next vulnerability affects your stack