CVE-2026-64514: In the Linux kernel, the following vulnerability has been resolved: userfaultfd: gate must_wait writability check on pte_present() userfaultfd_must_...

Description

In the Linux kernel, the following vulnerability has been resolved: userfaultfd: gate must_wait writability check on pte_present() userfaultfd_must_wait() and userfaultfd_huge_must_wait() read the PTE without taking the page table lock and then apply pte_write() / huge_pte_write() to it. Those accessors decode bits from the present encoding only; on a swap or migration entry they read the offset bits that happen to share the same position and return an undefined result. The intent of the check is "is this fault still WP-blocked?". A non-marker swap entry means the page is in transit -- the userfault context the original fault delivered against is no longer the same, and the swap-in or migration completion path will re-deliver a fresh fault if userspace still needs to handle it. Worst case under the current code the garbage write bit says "wait", and the thread stays asleep until a UFFDIO_WAKE that may never arrive. Gate the writability check on pte_present() so the lockless re-check only inspects present-PTE bits when the entry is actually present. The non-present, non-marker case returns "don't wait" and lets the fault path retry.

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 369cd2121be440543280b91056de187f625d0dbb, < a5700a4c1c9099ac2ac73fe8a09cf059972e0d2f; >= 369cd2121be440543280b91056de187f625d0dbb, < d4026417e8184d13850a0bad4d96ceb6ed9f7152; >= 369cd2121be440543280b91056de187f625d0dbb, < 29e6f952c5fb7dc1d6b90fe5b7f36063d44ddae0; >= 369cd2121be440543280b91056de187f625d0dbb, < 5f4dbdb0a87596214076b20b94f2b71b522170b3; >= 369cd2121be440543280b91056de187f625d0dbb, < a6e9a4939e359599701b1da351e84f72e021443a; >= 369cd2121be440543280b91056de187f625d0dbb, < 60d696a037eeeedfb57756dfe7ec08a1587c8631; >= 369cd2121be440543280b91056de187f625d0dbb, < 710183888174639a15fcec16cd1af766b8480bb7; >= 369cd2121be440543280b91056de187f625d0dbb, < 8e80af52db652fbc41320eee45a4f73bc029faf2
Linux	Linux	4.11

References

Timeline

Published: Jul 25, 2026
Last Modified: Jul 25, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-64514?

In the Linux kernel, the following vulnerability has been resolved: userfaultfd: gate must_wait writability check on pte_present() userfaultfd_must_wait() and userfaultfd_huge_must_wait() read the PTE without taking the page table lock and then apply pte_write() / huge_pte_write() to it. Those accessors decode bits from the present encoding only; on a swap or migration entry they read the offset bits that happen to share the same position and return an undefined result. The intent of the check is "is this fault still WP-blocked?". A non-marker swap entry means the page is in transit -- the userfault context the original fault delivered against is no longer the same, and the swap-in or migration completion path will re-deliver a fresh fault if userspace still needs to handle it. Worst case under the current code the garbage write bit says "wait", and the thread stays asleep until a UFFDIO_WAKE that may never arrive. Gate the writability check on pte_present() so the lockless re-check only inspects present-PTE bits when the entry is actually present. The non-present, non-marker case returns "don't wait" and lets the fault path retry.

How severe is CVE-2026-64514?

Severity scoring for CVE-2026-64514 is pending analysis.

How do I fix CVE-2026-64514?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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