# CVE-2025-21815: mm/compaction: fix UBSAN shift-out-of-bounds warning

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2025-02-27 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 6.7

## Description

In the Linux kernel, the following vulnerability has been resolved: mm/compaction: fix UBSAN shift-out-of-bounds warning syzkaller reported a UBSAN shift-out-of-bounds warning of (1UL << order) in isolate_freepages_block(). The bogus compound_order can be any value because it is union with flags. Add back the MAX_PAGE_ORDER check to fix the warning.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
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## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/4491159774d973a9e2e998d25d8fbb20fada6dfa
- https://git.kernel.org/stable/c/10b7d3eb535098ccd4c82a182a33655d8a0e5c88
- https://git.kernel.org/stable/c/d1366e74342e75555af2648a2964deb2d5c92200

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Page: https://cve.now/CVE-2025-21815
JSON: https://cve.now/api/v1/entries/CVE-2025-21815
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