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Fencer Vulns
high 7.5

CVE-2025-38523 json

cifs: Fix the smbd_response slab to allow usercopy

published 2025-08-16 14 mo ago modified 2026-08-05 3 mo ago also EUVD-2025-27882

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 33%
public exploits
0
none known

Summary

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

cifs: Fix the smbd_response slab to allow usercopy

The handling of received data in the smbdirect client code involves using copy_to_iter() to copy data from the smbd_reponse struct's packet trailer to a folioq buffer provided by netfslib that encapsulates a chunk of pagecache.

If, however, CONFIG_HARDENED_USERCOPY=y, this will result in the checks then performed in copy_to_iter() oopsing with something like the following:

CIFS: Attempting to mount //172.31.9.1/test CIFS: VFS: RDMA transport established usercopy: Kernel memory exposure attempt detected from SLUB object 'smbd_response_0000000091e24ea1' (offset 81, size 63)! ------------[ cut here ]------------ kernel BUG at mm/usercopy.c:102! ... RIP: 0010:usercopy_abort+0x6c/0x80 ... Call Trace: <TASK> __check_heap_object+0xe3/0x120 __check_object_size+0x4dc/0x6d0 smbd_recv+0x77f/0xfe0 [cifs] cifs_readv_from_socket+0x276/0x8f0 [cifs] cifs_read_from_socket+0xcd/0x120 [cifs] cifs_demultiplex_thread+0x7e9/0x2d50 [cifs] kthread+0x396/0x830 ret_from_fork+0x2b8/0x3b0 ret_from_fork_asm+0x1a/0x30

The problem is that the smbd_response slab's packet field isn't marked as being permitted for usercopy.

Fix this by passing parameters to kmem_slab_create() to indicate that copy_to_iter() is permitted from the packet region of the smbd_response slab objects, less the header space.

Patch / fix

  • Linux Linux 6.12.36, 6.15.8, 6.16
  • linux Debian 14, Debian 13 6.12.37-1

debian advisories DEBIAN-CVE-2025-38523

  • linux-aws-6.14 Ubuntu 24.04 LTS 6.14.0-1015.15~24.04.1
  • linux-gcp-6.14 Ubuntu 24.04 LTS 6.14.0-1018.19~24.04.1
  • linux-oem-6.14 Ubuntu 24.04 LTS 6.14.0-1014.14
  • linux-azure-6.14 Ubuntu 24.04 LTS 6.14.0-1014.14~24.04.1
  • linux-riscv-6.14 Ubuntu 24.04 LTS 6.14.0-34.34.1~24.04.1
  • linux-oracle-6.14 Ubuntu 24.04 LTS 6.14.0-1015.15~24.04.1
  • linux-azure-nvidia-6.14 Ubuntu 24.04 LTS 6.14.0-1007.7
  • linux-realtime-6.14 Ubuntu Pro Realtime 24.04 LTS 6.14.0-1014.14~24.04.1

ubuntu advisories UBUNTU-CVE-2025-38523

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 10.0 6.12.0-55.37.1.el10_0
  • rv RHEL 10.0 6.12.0-55.37.1.el10_0
  • perf RHEL 10.0 6.12.0-55.37.1.el10_0
  • rtla RHEL 10.0 6.12.0-55.37.1.el10_0
  • libperf RHEL 10.0 6.12.0-55.37.1.el10_0
  • kernel-rt RHEL 10.0 6.12.0-55.37.1.el10_0
  • kernel-64k RHEL 10.0 6.12.0-55.37.1.el10_0
  • kernel-core RHEL 10.0 6.12.0-55.37.1.el10_0

red hat advisories RHSA-2025:16904

  • kernel-abi-stablelists AlmaLinux 10 6.12.0-55.37.1.el10_0

almalinux advisories ALSA-2025:16904

  • kernel Rocky Linux 10 6.12.0-55.37.1.el10_0

rocky linux advisories RLSA-2025:16904

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-2025-38523 updated cvss 7.0

kernel: cifs: Fix the smbd_response slab to allow usercopy

  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-55.37.1.el10_0, perf 6.12.0-55.37.1.el10_0, rtla 6.12.0-55.37.1.el10_0, python3-perf 6.12.0-55.37.1.el10_0, kernel-devel-matched 6.12.0-55.37.1.el10_0, kernel-64k-devel-matched 6.12.0-55.37.1.el10_0, +7 more Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-55.37.1.el10_0, kernel-64k 6.12.0-55.37.1.el10_0, kernel-core 6.12.0-55.37.1.el10_0, kernel-tools 6.12.0-55.37.1.el10_0, kernel-modules 6.12.0-55.37.1.el10_0, kernel-64k-core 6.12.0-55.37.1.el10_0, +27 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-55.37.1.el10_0, kernel-debuginfo-common-s390x 6.12.0-55.37.1.el10_0, kernel-debuginfo-common-x86_64 6.12.0-55.37.1.el10_0, kernel-debuginfo-common-aarch64 6.12.0-55.37.1.el10_0, kernel-debuginfo-common-ppc64le 6.12.0-55.37.1.el10_0 Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-55.37.1.el10_0, kernel-rt-64k 6.12.0-55.37.1.el10_0, kernel-rt-core 6.12.0-55.37.1.el10_0, kernel-rt-modules 6.12.0-55.37.1.el10_0, kernel-rt-64k-core 6.12.0-55.37.1.el10_0, kernel-rt-debug-core 6.12.0-55.37.1.el10_0, +14 more Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-55.37.1.el10_0, kernel-rt-kvm 6.12.0-55.37.1.el10_0, kernel-rt-core 6.12.0-55.37.1.el10_0, kernel-rt-modules 6.12.0-55.37.1.el10_0, kernel-rt-debug-kvm 6.12.0-55.37.1.el10_0, kernel-rt-debug-core 6.12.0-55.37.1.el10_0, +6 more
    fixed: vendor fix RHSA-2025:16904
  • 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
    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

0.39% chance of exploitation in the next 30 days, higher than 33% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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

Weakness
  • CWE-1188 Initialization of a Resource with an Insecure Default
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.