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Fencer Vulns
medium 5.5

CVE-2026-52944 json

ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE

published 2026-06-24 4 mo ago modified 2026-09-14 56 d ago also EUVD-2026-38734

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:

ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE

FSCTL_SET_SPARSE in fsctl_set_sparse() modifies the file's sparse attribute and saves it through xattr without any permission checks.

This exposes two issues:

1) A client on a read-only share can change the sparse attribute on files it opened, even though the share is read-only. Other FSCTL write operations already check test_tree_conn_flag(work->tcon, KSMBD_TREE_CONN_FLAG_WRITABLE), but FSCTL_SET_SPARSE does not.

2) Even on writable shares, clients without FILE_WRITE_DATA or FILE_WRITE_ATTRIBUTES access should not modify the sparse attribute. Similar handle-level checks exist in other functions but are missing here.

Add both share-level writable check and per-handle access check. Use goto out on error to avoid leaking file references.

Patch / fix

  • Linux Linux 5.15.221, 6.1.188, 6.6.143, 6.12.110, 6.18.35, 7.0.12, 7.1
  • linux Debian 12 6.1.190-1
  • linux Debian 13 6.12.111-1
  • linux Debian 14 7.0.12-1
  • linux-6.12 Debian 12 6.12.111-1~deb12u1

debian advisories DEBIAN-CVE-2026-52944

  • linux Ubuntu 22.04 LTS 5.15.0-202.212
  • linux Ubuntu 24.04 LTS 6.8.0-146.146
  • linux Ubuntu 26.04 LTS 7.0.0-28.28
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1119.126
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1066.69
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1009.9
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1120.130
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1070.78

ubuntu advisories UBUNTU-CVE-2026-52944

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

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-2026-52944 updated

kernel: ksmbd: fix FSCTL permission bypass by adding a permission check for FSCTL_SET_SPARSE

  • 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 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
    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

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.