CVE-2026-97876
Description
A flaw was found in GRUB2. The bootloader insufficiently validates memory addresses passed to the serial configuration command, allowing arbitrary system memory to be targeted instead of a legitimate serial communication device. A local attacker with control over GRUB's boot configuration can exploit this issue to overwrite internal verification structures. This vulnerability allows the attacker to bypass Secure Boot lockdown restrictions and load arbitrary unsigned modules during system boot.
Mitigation
There is no complete mitigation for this issue other than applying a fixed GRUB build; the underlying fix requires validating the UART/MMIO resource used by the serial command and making the module-verification path fail closed when the verifier list is empty under lockdown.
Until a fixed build is available, exposure can be reduced by:
- Restricting who can modify or supply GRUB boot configuration (grub.cfg) and disallowing untrusted or attacker-controlled removable boot media.
- Avoiding use of the serial console/terminal_input during boot on systems relying on Secure Boot lockdown, where serial input is not otherwise required.
- Treating administrator-level control over boot configuration as equivalent to the ability to bypass lockdown module verification on affected GRUB builds, and applying the same access controls accordingly.
These steps reduce the attack surface but do not close the underlying validation flaw; they do not help if the attacker already controls boot configuration or removable boot media.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert: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 Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.4 | N/A | 6.4 |
| Attack Vector | Local | N/A | Local |
| Attack Complexity | High | N/A | High |
| Privileges Required | High | N/A | High |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | High | N/A | High |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
If the dereferencing operation is for a read, then the attack might allow reading of sensitive data, cause a crash, or set a variable to an unexpected value (since the value will be read from an unexpected memory location).
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If the untrusted pointer references a memory location that is not accessible to the product, or points to a location that is "malformed" or larger than expected by a read or write operation, the application may terminate unexpectedly.
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands; Modify Memory
If the pointer is dereferenced for a write operation, the attack might allow modification of critical state variables, cause a crash, or execute code. If the untrusted pointer is used in a function call, then the attacker might be able to call arbitrary functions.
Acknowledgements
Red Hat would like to thank luppa for reporting this issue.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
