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Fencer Vulns
critical 9.8

CVE-2026-68388 in the critical feed json

smb/client: handle overlapping allocated ranges in fallocate

published 2026-08-10 2 mo ago modified 2026-10-19 20 d ago also EUVD-2026-55574

cvss
9.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 44%
public exploits
0
none known

Summary

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

smb/client: handle overlapping allocated ranges in fallocate

smb3_simple_fallocate_range() can skip holes when an allocated range returned by the server starts before the current fallocate offset. The skipped hole is not zero-filled, but fallocate still returns success. A later write to that hole may therefore fail with ENOSPC.

The function queries allocated ranges so that it can preserve existing contents and write zeroes only into holes. However, the server may return a range that starts before the current fallocate offset.

For example, assume the fallocate request is [100, 400) and the only allocated range returned by the server is [0, 200):

Request: [100, 400) Server range: [ 0, 200) allocated

Correct: [100, 200) allocated data, skip [200, 400) hole, zero-fill

Current: [100, 300) skipped [300, 400) zero-filled afterwards

The current code adds the full server range length, 200, to the current offset 100 and moves to 300. As a result, the hole in [200, 300) is skipped without being zero-filled.

Fix this by advancing only over the part of the allocated range that overlaps the current fallocate offset. Ignore ranges that end before the current offset and reject ranges whose end offset overflows.

This also prevents a malformed range length from causing an out-of-bounds zero-buffer read.

Patch / fix

  • Linux Linux 5.10.265, 5.13, 5.14, 5.15.216, 6.1.183, 6.6.148, 6.12.101, 6.18.42, 7.1.6, 7.2
  • linux Debian 12 6.1.187-1
  • linux Debian 13 6.12.101-1
  • linux Debian 14 7.1.6-1
  • linux-6.12 Debian 12 6.12.101-1~deb12u1

debian advisories DEBIAN-CVE-2026-68388

  • linux Ubuntu 22.04 LTS 5.15.0-198.208
  • linux Ubuntu 24.04 LTS 6.8.0-147.147
  • linux Ubuntu 26.04 LTS 7.0.0-38.38
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1117.124
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1067.70
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1014.14
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1118.128
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1071.79

ubuntu advisories UBUNTU-CVE-2026-68388

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 8 4.18.0-553.157.1.el8_10
  • perf RHEL 8 4.18.0-553.157.1.el8_10
  • bpftool RHEL 8 4.18.0-553.157.1.el8_10
  • kernel-core RHEL 8 4.18.0-553.157.1.el8_10
  • kernel-tools RHEL 8 4.18.0-553.157.1.el8_10
  • python3-perf RHEL 8 4.18.0-553.157.1.el8_10
  • kernel-modules RHEL 8 4.18.0-553.157.1.el8_10
  • kernel-zfcpdump RHEL 8 4.18.0-553.157.1.el8_10

red hat advisories RHSA-2026:57253RHSA-2026:57254RHSA-2026:57252RHSA-2026:57251

  • kernel-source Linux Micro 6.0 6.4.0-159998.55.1
  • kernel-default Linux Micro 6.0 6.4.0-159998.55.1
  • kernel-kvmsmall Linux Micro 6.0 6.4.0-159998.55.1
  • kernel-default-base Linux Micro 6.0 6.4.0-159998.55.1.159998.21.42
  • kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.90.1
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.90.1
  • kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.53.90.1
  • kernel-source SLE Module for Development Tools 15 SP7, SLE Module for Basesystem 15 SP7 6.4.0-150700.53.90.1

suse advisories SUSE-SU-2026:5121-1SUSE-SU-2026:24550-1SUSE-SU-2026:5091-1

  • kernel AlmaLinux 10 6.12.0-211.49.1.el10_2
  • rv AlmaLinux 10 6.12.0-211.49.1.el10_2
  • perf AlmaLinux 10 6.12.0-211.49.1.el10_2
  • rtla AlmaLinux 10 6.12.0-211.49.1.el10_2
  • libperf AlmaLinux 10 6.12.0-211.49.1.el10_2
  • kernel-rt AlmaLinux 10 6.12.0-211.49.1.el10_2
  • kernel-64k AlmaLinux 10 6.12.0-211.49.1.el10_2
  • kernel-core AlmaLinux 10 6.12.0-211.49.1.el10_2

almalinux advisories ALSA-2026:57251ALSA-2026:57252ALSA-2026:57253ALSA-2026:57254

  • kernel Rocky Linux 10 6.12.0-211.49.1.el10_2
  • kernel Rocky Linux 9 5.14.0-687.41.1.el9_8
  • kernel-rt Rocky Linux 8 4.18.0-553.157.1.rt7.498.el8_10
  • kernel Rocky Linux 8 4.18.0-553.157.1.el8_10

rocky linux advisories RLSA-2026:57251RLSA-2026:57252RLSA-2026:57254RLSA-2026:57253

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-2026-68388 updated cvss 7.0

kernel: smb/client: handle overlapping allocated ranges in fallocate

  • 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
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-687.41.1.el9_8, perf 5.14.0-687.41.1.el9_8, rtla 5.14.0-687.41.1.el9_8, python3-perf 5.14.0-687.41.1.el9_8, kernel-devel-matched 5.14.0-687.41.1.el9_8, kernel-64k-devel-matched 5.14.0-687.41.1.el9_8, +7 more
    fixed: vendor fix RHSA-2026:57252
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-211.49.1.el10_2, perf 6.12.0-211.49.1.el10_2, rtla 6.12.0-211.49.1.el10_2, python3-perf 6.12.0-211.49.1.el10_2, kernel-devel-matched 6.12.0-211.49.1.el10_2, kernel-64k-devel-matched 6.12.0-211.49.1.el10_2, +7 more
    fixed: vendor fix RHSA-2026:57251
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.157.1.el8_10, kernel 4.18.0-553.157.1.el8_10, bpftool 4.18.0-553.157.1.el8_10, kernel-core 4.18.0-553.157.1.el8_10, kernel-tools 4.18.0-553.157.1.el8_10, python3-perf 4.18.0-553.157.1.el8_10, +15 more
    fixed: vendor fix RHSA-2026:57253
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-687.41.1.el9_8, kernel-64k 5.14.0-687.41.1.el9_8, kernel-core 5.14.0-687.41.1.el9_8, kernel-tools 5.14.0-687.41.1.el9_8, kernel-modules 5.14.0-687.41.1.el9_8, kernel-64k-core 5.14.0-687.41.1.el9_8, +27 more
    fixed: vendor fix RHSA-2026:57252
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-211.49.1.el10_2, kernel-64k 6.12.0-211.49.1.el10_2, kernel-core 6.12.0-211.49.1.el10_2, kernel-tools 6.12.0-211.49.1.el10_2, kernel-modules 6.12.0-211.49.1.el10_2, kernel-64k-core 6.12.0-211.49.1.el10_2, +28 more
    fixed: vendor fix RHSA-2026:57251
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-687.41.1.el9_8, kernel-debuginfo-common-s390x 5.14.0-687.41.1.el9_8, kernel-debuginfo-common-x86_64 5.14.0-687.41.1.el9_8, kernel-debuginfo-common-aarch64 5.14.0-687.41.1.el9_8, kernel-debuginfo-common-ppc64le 5.14.0-687.41.1.el9_8
    fixed: vendor fix RHSA-2026:57252
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-211.49.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.49.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.49.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.49.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.49.1.el10_2
    fixed: vendor fix RHSA-2026:57251
show 8 more
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.157.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.157.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.157.1.el8_10
    fixed: vendor fix RHSA-2026:57253
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.157.1.rt7.498.el8_10, kernel-rt-kvm 4.18.0-553.157.1.rt7.498.el8_10, kernel-rt-core 4.18.0-553.157.1.rt7.498.el8_10, kernel-rt-modules 4.18.0-553.157.1.rt7.498.el8_10, kernel-rt-debug-kvm 4.18.0-553.157.1.rt7.498.el8_10, kernel-rt-debug-core 4.18.0-553.157.1.rt7.498.el8_10, +4 more
    fixed: vendor fix RHSA-2026:57254
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-687.41.1.el9_8, kernel-rt-64k 5.14.0-687.41.1.el9_8, kernel-rt-core 5.14.0-687.41.1.el9_8, kernel-rt-modules 5.14.0-687.41.1.el9_8, kernel-rt-64k-core 5.14.0-687.41.1.el9_8, kernel-rt-debug-core 5.14.0-687.41.1.el9_8, +14 more
    fixed: vendor fix RHSA-2026:57252
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-211.49.1.el10_2, kernel-rt-64k 6.12.0-211.49.1.el10_2, kernel-rt-core 6.12.0-211.49.1.el10_2, kernel-rt-modules 6.12.0-211.49.1.el10_2, kernel-rt-64k-core 6.12.0-211.49.1.el10_2, kernel-rt-debug-core 6.12.0-211.49.1.el10_2, +14 more
    fixed: vendor fix RHSA-2026:57251
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-687.41.1.el9_8, kernel-rt-core 5.14.0-687.41.1.el9_8, kernel-rt-modules 5.14.0-687.41.1.el9_8, kernel-rt-debug-core 5.14.0-687.41.1.el9_8, kernel-rt-modules-core 5.14.0-687.41.1.el9_8, kernel-rt-debug-modules 5.14.0-687.41.1.el9_8, +4 more
    fixed: vendor fix RHSA-2026:57252
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-211.49.1.el10_2, kernel-rt-core 6.12.0-211.49.1.el10_2, kernel-rt-modules 6.12.0-211.49.1.el10_2, kernel-rt-debug-core 6.12.0-211.49.1.el10_2, kernel-rt-modules-core 6.12.0-211.49.1.el10_2, kernel-rt-debug-modules 6.12.0-211.49.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:57251
  • Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.157.1.rt7.498.el8_10, kernel-rt-core 4.18.0-553.157.1.rt7.498.el8_10, kernel-rt-modules 4.18.0-553.157.1.rt7.498.el8_10, kernel-rt-debug-core 4.18.0-553.157.1.rt7.498.el8_10, kernel-rt-debug-modules 4.18.0-553.157.1.rt7.498.el8_10, kernel-rt-modules-extra 4.18.0-553.157.1.rt7.498.el8_10, +2 more
    fixed: vendor fix RHSA-2026:57254
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 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
yes
Technical impact
total
Assessed
23 d ago

Exploit prediction

0.51% chance of exploitation in the next 30 days, higher than 44% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Linux Linux

Classification

Weakness
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.