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

• Severity: high (CVSS 7.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-02-27 · updated 2026-06-17
• Weakness: CWE-125

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.

Affected products

• Linux kernel: from 6.7 before 6.12.14; from 6.13 before 6.13.3 — fixed in 6.12.14, 6.13.3

How to fix

Upgrade to a fixed version: Linux kernel 6.12.14, 6.13.3. Check the vendor advisory for mitigations.

References

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

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