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Fencer Vulns
medium 5.5

CVE-2025-68211 json

ksm: use range-walk function to jump over holes in scan_get_next_rmap_item

published 2025-12-16 10 mo ago modified 2026-10-14 25 d ago also EUVD-2025-203685

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 3%
public exploits
0
none known

Summary

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

ksm: use range-walk function to jump over holes in scan_get_next_rmap_item

Currently, scan_get_next_rmap_item() walks every page address in a VMA to locate mergeable pages. This becomes highly inefficient when scanning large virtual memory areas that contain mostly unmapped regions, causing ksmd to use large amount of cpu without deduplicating much pages.

This patch replaces the per-address lookup with a range walk using walk_page_range(). The range walker allows KSM to skip over entire unmapped holes in a VMA, avoiding unnecessary lookups. This problem was previously discussed in [1].

Consider the following test program which creates a 32 TiB mapping in the virtual address space but only populates a single page:

#include <unistd.h> #include <stdio.h> #include <sys/mman.h>

/* 32 TiB */ const size_t size = 32ul * 1024 * 1024 * 1024 * 1024;

int main() { char *area = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_NORESERVE | MAP_PRIVATE | MAP_ANON, -1, 0);

if (area == MAP_FAILED) { perror("mmap() failed\n"); return -1; }

/* Populate a single page such that we get an anon_vma. */ *area = 0;

/* Enable KSM. */ madvise(area, size, MADV_MERGEABLE); pause(); return 0; }

$ ./ksm-sparse & $ echo 1 > /sys/kernel/mm/ksm/run

Without this patch ksmd uses 100% of the cpu for a long time (more then 1 hour in my test machine) scanning all the 32 TiB virtual address space that contain only one mapped page. This makes ksmd essentially deadlocked not able to deduplicate anything of value. With this patch ksmd walks only the one mapped page and skips the rest of the 32 TiB virtual address space, making the scan fast using little cpu.

Patch / fix

  • Linux Linux 5.10.249, 5.15.199, 6.1.161, 6.6.121, 6.12.59, 6.17.9, 6.18
  • linux Debian 12 6.1.162-1
  • linux Debian 13 6.12.63-1
  • linux Debian 14 6.17.9-1

debian advisories DEBIAN-CVE-2025-68211

  • linux Ubuntu 22.04 LTS 5.15.0-176.186
  • linux Ubuntu 25.10 6.17.0-14.14
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1105.112
  • linux-aws Ubuntu 25.10 6.17.0-1007.7
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1105.114
  • linux-gcp Ubuntu 25.10 6.17.0-1007.7
  • linux-gke Ubuntu 22.04 LTS 5.15.0-1101.107
  • linux-ibm Ubuntu 22.04 LTS 5.15.0-1099.102

ubuntu advisories UBUNTU-CVE-2025-68211

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 RHEL 9 5.14.0-687.42.1.el9_8
  • rv RHEL 9 5.14.0-687.42.1.el9_8
  • perf RHEL 9 5.14.0-687.42.1.el9_8
  • rtla RHEL 9 5.14.0-687.42.1.el9_8
  • libperf RHEL 9 5.14.0-687.42.1.el9_8
  • kernel-rt RHEL 9 5.14.0-687.42.1.el9_8
  • kernel-64k RHEL 9 5.14.0-687.42.1.el9_8
  • kernel-core RHEL 9 5.14.0-687.42.1.el9_8

red hat advisories RHSA-2026:62568RHSA-2026:59723RHSA-2026:49211

  • kernel-rt Linux Micro 6.2 6.12.0-160000.26.1
  • kernel-64kb SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.26.1
  • kernel-source SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.26.1
  • kernel-default SLES 16.0, SLE High Availability Extension 16.0, Linux Micro 6.2 +1 more 6.12.0-160000.26.1
  • kernel-default-base SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.26.1.160000.2.7
  • kernel-syms SLES 16.0, Linux Micro Extras 6.2, SLES for SAP applications 16.0 6.12.0-160000.26.1
  • kernel-azure SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.26.1
  • kernel-obs-qa SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.26.1

suse advisories SUSE-SU-2026:20555-1SUSE-SU-2026:20599-1SUSE-SU-2026:20615-1SUSE-SU-2026:20570-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.26.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.26.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.26.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.26.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.26.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.26.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.26.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.26.1

opensuse advisories openSUSE-SU-2026:20287-1

  • kernel AlmaLinux 9 5.14.0-687.42.1.el9_8
  • rv AlmaLinux 9 5.14.0-687.42.1.el9_8
  • perf AlmaLinux 9 5.14.0-687.42.1.el9_8
  • rtla AlmaLinux 9 5.14.0-687.42.1.el9_8
  • libperf AlmaLinux 9 5.14.0-687.42.1.el9_8
  • kernel-rt AlmaLinux 9 5.14.0-687.42.1.el9_8
  • kernel-64k AlmaLinux 9 5.14.0-687.42.1.el9_8
  • kernel-core AlmaLinux 9 5.14.0-687.42.1.el9_8

almalinux advisories ALSA-2026:59723ALSA-2026:49211

  • kernel Rocky Linux 9 5.14.0-687.42.1.el9_8
  • kernel Rocky Linux 10 6.12.0-211.42.1.el10_2

rocky linux advisories RLSA-2026:59723RLSA-2026:49211

  • kernel Azure Linux 3.0 6.6.121.1-1
  • kernel CBL-Mariner 2.0 5.15.200.1-1

azure linux advisories AZL-72419AZL-78398

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

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-2025-68211 updated cvss 5.5

kernel: ksm: use range-walk function to jump over holes in scan_get_next_rmap_item

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: no fix planned “Out of support scope”
  • 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 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 more
    affected: no fix available “Fix deferred”
  • Red Hat CodeReady Linux Builder EUS (v.9.6) libperf 5.14.0-570.138.1.el9_6, kernel-debuginfo-common-s390x 5.14.0-570.138.1.el9_6, kernel-debuginfo-common-x86_64 5.14.0-570.138.1.el9_6, kernel-debuginfo-common-aarch64 5.14.0-570.138.1.el9_6, kernel-debuginfo-common-ppc64le 5.14.0-570.138.1.el9_6
    fixed: vendor fix RHSA-2026:62568
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-687.42.1.el9_8, perf 5.14.0-687.42.1.el9_8, rtla 5.14.0-687.42.1.el9_8, python3-perf 5.14.0-687.42.1.el9_8, kernel-devel-matched 5.14.0-687.42.1.el9_8, kernel-64k-devel-matched 5.14.0-687.42.1.el9_8, +7 more
    fixed: vendor fix RHSA-2026:59723
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-211.42.1.el10_2, perf 6.12.0-211.42.1.el10_2, rtla 6.12.0-211.42.1.el10_2, python3-perf 6.12.0-211.42.1.el10_2, kernel-devel-matched 6.12.0-211.42.1.el10_2, kernel-64k-devel-matched 6.12.0-211.42.1.el10_2, +7 more
    fixed: vendor fix RHSA-2026:49211
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) rv 5.14.0-570.138.1.el9_6, perf 5.14.0-570.138.1.el9_6, rtla 5.14.0-570.138.1.el9_6, python3-perf 5.14.0-570.138.1.el9_6, kernel-devel-matched 5.14.0-570.138.1.el9_6, kernel-64k-devel-matched 5.14.0-570.138.1.el9_6, +7 more
    fixed: vendor fix RHSA-2026:62568
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-687.42.1.el9_8, kernel-64k 5.14.0-687.42.1.el9_8, kernel-core 5.14.0-687.42.1.el9_8, kernel-tools 5.14.0-687.42.1.el9_8, kernel-modules 5.14.0-687.42.1.el9_8, kernel-64k-core 5.14.0-687.42.1.el9_8, +27 more
    fixed: vendor fix RHSA-2026:59723
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-211.42.1.el10_2, kernel-64k 6.12.0-211.42.1.el10_2, kernel-core 6.12.0-211.42.1.el10_2, kernel-tools 6.12.0-211.42.1.el10_2, kernel-modules 6.12.0-211.42.1.el10_2, kernel-64k-core 6.12.0-211.42.1.el10_2, +28 more
    fixed: vendor fix RHSA-2026:49211
show 9 more
  • Red Hat Enterprise Linux BaseOS EUS (v.9.6) kernel 5.14.0-570.138.1.el9_6, kernel-64k 5.14.0-570.138.1.el9_6, kernel-core 5.14.0-570.138.1.el9_6, kernel-tools 5.14.0-570.138.1.el9_6, kernel-modules 5.14.0-570.138.1.el9_6, kernel-64k-core 5.14.0-570.138.1.el9_6, +27 more
    fixed: vendor fix RHSA-2026:62568
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-687.42.1.el9_8, kernel-debuginfo-common-s390x 5.14.0-687.42.1.el9_8, kernel-debuginfo-common-x86_64 5.14.0-687.42.1.el9_8, kernel-debuginfo-common-aarch64 5.14.0-687.42.1.el9_8, kernel-debuginfo-common-ppc64le 5.14.0-687.42.1.el9_8
    fixed: vendor fix RHSA-2026:59723
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-211.42.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.42.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.42.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.42.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.42.1.el10_2
    fixed: vendor fix RHSA-2026:49211
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-687.42.1.el9_8, kernel-rt-64k 5.14.0-687.42.1.el9_8, kernel-rt-core 5.14.0-687.42.1.el9_8, kernel-rt-modules 5.14.0-687.42.1.el9_8, kernel-rt-64k-core 5.14.0-687.42.1.el9_8, kernel-rt-debug-core 5.14.0-687.42.1.el9_8, +14 more
    fixed: vendor fix RHSA-2026:59723
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-211.42.1.el10_2, kernel-rt-64k 6.12.0-211.42.1.el10_2, kernel-rt-core 6.12.0-211.42.1.el10_2, kernel-rt-modules 6.12.0-211.42.1.el10_2, kernel-rt-64k-core 6.12.0-211.42.1.el10_2, kernel-rt-debug-core 6.12.0-211.42.1.el10_2, +14 more
    fixed: vendor fix RHSA-2026:49211
  • Red Hat Enterprise Linux Real Time EUS (v.9.6) kernel-rt 5.14.0-570.138.1.el9_6, kernel-rt-64k 5.14.0-570.138.1.el9_6, kernel-rt-core 5.14.0-570.138.1.el9_6, kernel-rt-modules 5.14.0-570.138.1.el9_6, kernel-rt-64k-core 5.14.0-570.138.1.el9_6, kernel-rt-debug-core 5.14.0-570.138.1.el9_6, +14 more
    fixed: vendor fix RHSA-2026:62568
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-687.42.1.el9_8, kernel-rt-core 5.14.0-687.42.1.el9_8, kernel-rt-modules 5.14.0-687.42.1.el9_8, kernel-rt-debug-core 5.14.0-687.42.1.el9_8, kernel-rt-modules-core 5.14.0-687.42.1.el9_8, kernel-rt-debug-modules 5.14.0-687.42.1.el9_8, +4 more
    fixed: vendor fix RHSA-2026:59723
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-211.42.1.el10_2, kernel-rt-core 6.12.0-211.42.1.el10_2, kernel-rt-modules 6.12.0-211.42.1.el10_2, kernel-rt-debug-core 6.12.0-211.42.1.el10_2, kernel-rt-modules-core 6.12.0-211.42.1.el10_2, kernel-rt-debug-modules 6.12.0-211.42.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:49211
  • Red Hat Enterprise Linux Real Time for NFV EUS (v.9.6) kernel-rt 5.14.0-570.138.1.el9_6, kernel-rt-kvm 5.14.0-570.138.1.el9_6, kernel-rt-core 5.14.0-570.138.1.el9_6, kernel-rt-modules 5.14.0-570.138.1.el9_6, kernel-rt-debug-kvm 5.14.0-570.138.1.el9_6, kernel-rt-debug-core 5.14.0-570.138.1.el9_6, +6 more
    fixed: vendor fix RHSA-2026:62568

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
4 mo ago

Exploit prediction

0.15% chance of exploitation in the next 30 days, higher than 3% 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.