# CVE-2025-61661: GNU GRUB2 out-of-bounds write in grub_usb_get_string

Source: https://junglewise.ai/threats/cve-2025-61661-gnu-grub2-out-of-bounds-write-in-grub-usb-get-string  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-11-18. Updated: 2026-06-25  
License: CC BY 4.0 with a link back

CVE-2025-61661 · Severity: medium · CVSS 4.8 · Published 2025-11-18

A vulnerability in the GRUB bootloader, which is used to start many Linux-based operating systems, could allow an attacker with physical access to crash a system. By plugging in a specially crafted USB device during the boot process, an attacker can trigger a memory error that causes the computer to stop responding or potentially corrupt data. This issue primarily impacts system availability during the startup phase.

## Quick answers

**Is CVE-2025-61661 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-61661 being exploited in the wild.

**How severe is CVE-2025-61661?** Medium severity, with a CVSS score of 4.8, published 18 November 2025.

**Which products and versions are affected?** GNU Project GRUB2 All versions prior to November 2025 patches.

**Is there a fix for CVE-2025-61661?** A patch was published on 2025-11-18: Security patches submitted to GRUB development list Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2025-61661 attacked?** It is attacked with physical access, in an operating system.

**Am I affected by CVE-2025-61661?** Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A heap-based buffer overflow exists in GRUB2's 'grub_usb_get_string()' function within 'grub-core/commands/usbtest.c'. The vulnerability is caused by a time-of-check to time-of-use (TOCTOU) style inconsistency where the bootloader uses an initial length value from a USB descriptor for memory allocation, but subsequently uses a different length value from a second read during the UTF-16 to UTF-8 conversion. A local, physical attacker can connect a malicious USB device that provides inconsistent length descriptors to trigger an out-of-bounds write. This can result in a system crash (Denial of Service) or potentially limited data corruption. Patches have been developed to ensure the allocation and conversion use the same validated length field.

## Affected products

- GNU Project GRUB2 All versions prior to November 2025 patches

## Timeline

- 2025-11-10: other: Issue reported to Red Hat Bugzilla
- 2025-11-18: disclosed: Public disclosure and CVE assignment
- 2025-11-18: patched: Security patches submitted to GRUB development list

## References

- [https://git.savannah.gnu.org/git/grub.git](https://git.savannah.gnu.org/git/grub.git)
- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)
- [https://access.redhat.com/security/cve/CVE-2025-61661](https://access.redhat.com/security/cve/CVE-2025-61661)
- [https://bugzilla.redhat.com/show_bug.cgi?id=2413827](https://bugzilla.redhat.com/show_bug.cgi?id=2413827)
- [http://www.openwall.com/lists/oss-security/2025/11/18/8](http://www.openwall.com/lists/oss-security/2025/11/18/8)