VulnerabilityPublished 25 Jul 2026

CVE-2026-64514: Linux kernel · userfaultfd: gate must_wait writability check on pte_present()

Source GCVE Database

Not known to be exploited.

Data as of 26 Oct 2026, 12:55 UTC

Severity

Medium

Rated by Threat Radar · No CVSS score from NVD or the CNA

EPSS: 0.1% chance of exploitation in 30 days – higher than 7% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-r2gx-xm5r-33f5

What to do

AI-suggested

Since this is a Linux kernel vulnerability, monitor official Linux kernel security advisories for patches addressing CVE-2026-64514. Apply the official kernel updates once available to resolve the issue.

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.

Impact

The vulnerability can cause threads to stall indefinitely by waiting on a write protection block that is incorrectly detected due to misinterpreted PTE bits. This may lead to denial of service conditions where userfaultfd-related threads do not progress as expected. There is no indication of code execution or privilege escalation from the provided data.

Summary

The Linux kernel vulnerability CVE-2026-64514 concerns the userfaultfd interface's must_wait writability check on page table entries (PTEs). The affected functions read PTEs without acquiring the page table lock and apply write checks that only decode bits valid for present entries. When encountering swap or migration entries, these functions misinterpret offset bits as write bits, resulting in undefined behavior. This can cause a thread to remain asleep indefinitely, waiting for a wake event that may never occur. The fix involves gating the writability check on the presence of the PTE, ensuring that only present entries are checked for writability, and non-present entries return a 'don't wait' result to allow fault path retries.

References

Community reviews

Loading reviews…