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Fencer Vulns
medium 5.5

CVE-2026-31575 json

mm/userfaultfd: fix hugetlb fault mutex hash calculation

published 2026-04-24 6 mo ago modified 2026-11-05 3 d ago also EUVD-2026-25468

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 1%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

mm/userfaultfd: fix hugetlb fault mutex hash calculation

In mfill_atomic_hugetlb(), linear_page_index() is used to calculate the page index for hugetlb_fault_mutex_hash(). However, linear_page_index() returns the index in PAGE_SIZE units, while hugetlb_fault_mutex_hash() expects the index in huge page units. This mismatch means that different addresses within the same huge page can produce different hash values, leading to the use of different mutexes for the same huge page. This can cause races between faulting threads, which can corrupt the reservation map and trigger the BUG_ON in resv_map_release().

Fix this by introducing hugetlb_linear_page_index(), which returns the page index in huge page granularity, and using it in place of linear_page_index().

Patch / fix

  • Linux Linux 6.12.84, 6.18.24, 6.19.14, 7.0.1, 7.1
  • linux Debian 13 6.12.85-1
  • linux Debian 14 6.19.14-1

debian advisories DEBIAN-CVE-2026-31575

  • linux Ubuntu 24.04 LTS 6.8.0-136.136
  • linux Ubuntu 26.04 LTS 7.0.0-27.27
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1061.64
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1008.8
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1064.72
  • linux-gcp Ubuntu 26.04 LTS 7.0.0-1007.7
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1059.67
  • linux-ibm Ubuntu 24.04 LTS 6.8.0-1061.62

ubuntu advisories UBUNTU-CVE-2026-31575

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-rt Linux Micro 6.2 6.12.0-160000.34.1
  • kernel-64kb SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.34.1
  • kernel-source SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.34.1
  • kernel-default SLES 16.0, SLE High Availability Extension 16.0, Linux Micro 6.2 +1 more 6.12.0-160000.34.1
  • kernel-default-base SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.34.1.160000.2.15
  • kernel-syms SLES 16.0, Linux Micro Extras 6.2, SLES for SAP applications 16.0 6.12.0-160000.34.1
  • kernel-azure SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.34.1
  • kernel-obs-qa SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.34.1

suse advisories SUSE-SU-2026:22048-1SUSE-SU-2026:22087-1SUSE-SU-2026:22076-1SUSE-SU-2026:22043-1

  • kernel-source openSUSE Tumbleweed 7.0.3-1.1

opensuse advisories openSUSE-SU-2026:10703-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-31575 updated cvss 5.5

kernel: mm/userfaultfd: fix hugetlb fault mutex hash calculation

  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
3 d ago

Exploit prediction

0.12% chance of exploitation in the next 30 days, higher than 1% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.