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Fencer Intel
high 7.8

CVE-2025-39966 json

iommufd: Fix race during abort for file descriptors

published last yr. modified 21d ago also EUVD-2025-34606

cvss
7.8
version 3.1, CNA
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:

iommufd: Fix race during abort for file descriptors

fput() doesn't actually call file_operations release() synchronously, it puts the file on a work queue and it will be released eventually.

This is normally fine, except for iommufd the file and the iommufd_object are tied to gether. The file has the object as it's private_data and holds a users refcount, while the object is expected to remain alive as long as the file is.

When the allocation of a new object aborts before installing the file it will fput() the file and then go on to immediately kfree() the obj. This causes a UAF once the workqueue completes the fput() and tries to decrement the users refcount.

Fix this by putting the core code in charge of the file lifetime, and call __fput_sync() during abort to ensure that release() is called before kfree. __fput_sync() is a bit too tricky to open code in all the object implementations. Instead the objects tell the core code where the file pointer is and the core will take care of the life cycle.

If the object is successfully allocated then the file will hold a users refcount and the iommufd_object cannot be destroyed.

It is worth noting that close(); ioctl(IOMMU_DESTROY); doesn't have an issue because close() is already using a synchronous version of fput().

The UAF looks like this:

BUG: KASAN: slab-use-after-free in iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376 Write of size 4 at addr ffff888059c97804 by task syz.0.46/6164

CPU: 0 UID: 0 PID: 6164 Comm: syz.0.46 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline] print_report+0xcd/0x630 mm/kasan/report.c:482 kasan_report+0xe0/0x110 mm/kasan/report.c:595 check_region_inline mm/kasan/generic.c:183 [inline] kasan_check_range+0x100/0x1b0 mm/kasan/generic.c:189 instrument_atomic_read_write include/linux/instrumented.h:96 [inline] atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline] __refcount_dec include/linux/refcount.h:455 [inline] refcount_dec include/linux/refcount.h:476 [inline] iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376 __fput+0x402/0xb70 fs/file_table.c:468 task_work_run+0x14d/0x240 kernel/task_work.c:227 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] exit_to_user_mode_loop+0xeb/0x110 kernel/entry/common.c:43 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline] syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline] do_syscall_64+0x41c/0x4c0 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Patch / fix

  • Linux Linux 6.12.50, 6.16.10, 6.17
  • linux Debian 13 6.12.57-1
  • linux Debian 14 6.16.10-1

debian advisories DEBIAN-CVE-2025-39966

  • linux Ubuntu 25.10 6.17.0-6.6
  • linux-aws Ubuntu 25.10 6.17.0-1003.3
  • linux-gcp Ubuntu 25.10 6.17.0-1003.3
  • linux-azure Ubuntu 25.10 6.17.0-1006.6
  • linux-raspi Ubuntu 25.10 6.17.0-1004.4
  • linux-riscv Ubuntu 25.10 6.17.0-6.6.1
  • linux-oracle Ubuntu 25.10 6.17.0-1003.3
  • linux-realtime Ubuntu 25.10 6.17.0-1002.3

ubuntu advisories UBUNTU-CVE-2025-39966

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 10.1 6.12.0-124.27.1.el10_1
  • rv RHEL 10.1 6.12.0-124.27.1.el10_1
  • perf RHEL 10.1 6.12.0-124.27.1.el10_1
  • rtla RHEL 10.1 6.12.0-124.27.1.el10_1
  • libperf RHEL 10.1 6.12.0-124.27.1.el10_1
  • kernel-rt RHEL 10.1 6.12.0-124.27.1.el10_1
  • kernel-64k RHEL 10.1 6.12.0-124.27.1.el10_1
  • kernel-core RHEL 10.1 6.12.0-124.27.1.el10_1

red hat advisories RHSA-2026:0453RHSA-2025:23250RHSA-2025:23241RHSA-2025:22802

  • kernel-abi-stablelists AlmaLinux 10 6.12.0-124.27.1.el10_1
  • kernel AlmaLinux 9 5.14.0-611.16.1.el9_7
  • rv AlmaLinux 9 5.14.0-611.16.1.el9_7
  • perf AlmaLinux 9 5.14.0-611.16.1.el9_7
  • rtla AlmaLinux 9 5.14.0-611.16.1.el9_7
  • libperf AlmaLinux 9 5.14.0-611.16.1.el9_7
  • kernel-rt AlmaLinux 9 5.14.0-611.16.1.el9_7
  • kernel-64k AlmaLinux 9 5.14.0-611.16.1.el9_7

almalinux advisories ALSA-2026:0453ALSA-2025:23241

  • kernel Rocky Linux 10 6.12.0-124.27.1.el10_1
  • kernel Rocky Linux 9 5.14.0-611.16.1.el9_7

rocky linux advisories RLSA-2026:0453RLSA-2025:23241

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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-2025-39966 updated cvss 7.4

kernel: iommufd: Fix race during abort for file descriptors

  • 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: workaround, no fix available
  • Red Hat CodeReady Linux Builder EUS (v.9.6) libperf 5.14.0-570.72.1.el9_6, kernel-debuginfo-common-s390x 5.14.0-570.72.1.el9_6, kernel-debuginfo-common-x86_64 5.14.0-570.72.1.el9_6, kernel-debuginfo-common-aarch64 5.14.0-570.72.1.el9_6, kernel-debuginfo-common-ppc64le 5.14.0-570.72.1.el9_6
    fixed: vendor fix RHSA-2025:22802
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-611.16.1.el9_7, perf 5.14.0-611.16.1.el9_7, rtla 5.14.0-611.16.1.el9_7, python3-perf 5.14.0-611.16.1.el9_7, kernel-devel-matched 5.14.0-611.16.1.el9_7, kernel-64k-devel-matched 5.14.0-611.16.1.el9_7, +7 more
    fixed: vendor fix RHSA-2025:23241
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-124.27.1.el10_1, perf 6.12.0-124.27.1.el10_1, rtla 6.12.0-124.27.1.el10_1, python3-perf 6.12.0-124.27.1.el10_1, kernel-devel-matched 6.12.0-124.27.1.el10_1, kernel-64k-devel-matched 6.12.0-124.27.1.el10_1, +7 more
    fixed: vendor fix RHSA-2026:0453
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) rv 6.12.0-55.50.1.el10_0, perf 6.12.0-55.50.1.el10_0, rtla 6.12.0-55.50.1.el10_0, python3-perf 6.12.0-55.50.1.el10_0, kernel-devel-matched 6.12.0-55.50.1.el10_0, kernel-64k-devel-matched 6.12.0-55.50.1.el10_0, +7 more
    fixed: vendor fix RHSA-2025:23250
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) rv 5.14.0-570.72.1.el9_6, perf 5.14.0-570.72.1.el9_6, rtla 5.14.0-570.72.1.el9_6, python3-perf 5.14.0-570.72.1.el9_6, kernel-devel-matched 5.14.0-570.72.1.el9_6, kernel-64k-devel-matched 5.14.0-570.72.1.el9_6, +7 more
    fixed: vendor fix RHSA-2025:22802
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-611.16.1.el9_7, kernel-64k 5.14.0-611.16.1.el9_7, kernel-core 5.14.0-611.16.1.el9_7, kernel-tools 5.14.0-611.16.1.el9_7, kernel-modules 5.14.0-611.16.1.el9_7, kernel-64k-core 5.14.0-611.16.1.el9_7, +27 more
    fixed: vendor fix RHSA-2025:23241
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-124.27.1.el10_1, kernel-64k 6.12.0-124.27.1.el10_1, kernel-core 6.12.0-124.27.1.el10_1, kernel-tools 6.12.0-124.27.1.el10_1, kernel-modules 6.12.0-124.27.1.el10_1, kernel-64k-core 6.12.0-124.27.1.el10_1, +28 more
    fixed: vendor fix RHSA-2026:0453
show 14 more
  • Red Hat Enterprise Linux BaseOS EUS (v. 10.0) kernel 6.12.0-55.50.1.el10_0, kernel-64k 6.12.0-55.50.1.el10_0, kernel-core 6.12.0-55.50.1.el10_0, kernel-tools 6.12.0-55.50.1.el10_0, kernel-modules 6.12.0-55.50.1.el10_0, kernel-64k-core 6.12.0-55.50.1.el10_0, +27 more
    fixed: vendor fix RHSA-2025:23250
  • Red Hat Enterprise Linux BaseOS EUS (v.9.6) kernel 5.14.0-570.72.1.el9_6, kernel-64k 5.14.0-570.72.1.el9_6, kernel-core 5.14.0-570.72.1.el9_6, kernel-tools 5.14.0-570.72.1.el9_6, kernel-modules 5.14.0-570.72.1.el9_6, kernel-64k-core 5.14.0-570.72.1.el9_6, +27 more
    fixed: vendor fix RHSA-2025:22802
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-611.16.1.el9_7, kernel-debuginfo-common-s390x 5.14.0-611.16.1.el9_7, kernel-debuginfo-common-x86_64 5.14.0-611.16.1.el9_7, kernel-debuginfo-common-aarch64 5.14.0-611.16.1.el9_7, kernel-debuginfo-common-ppc64le 5.14.0-611.16.1.el9_7
    fixed: vendor fix RHSA-2025:23241
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-124.27.1.el10_1, kernel-debuginfo-common-s390x 6.12.0-124.27.1.el10_1, kernel-debuginfo-common-x86_64 6.12.0-124.27.1.el10_1, kernel-debuginfo-common-aarch64 6.12.0-124.27.1.el10_1, kernel-debuginfo-common-ppc64le 6.12.0-124.27.1.el10_1
    fixed: vendor fix RHSA-2026:0453
  • Red Hat Enterprise Linux CodeReady Linux Builder EUS (v. 10.0) libperf 6.12.0-55.50.1.el10_0, kernel-debuginfo-common-s390x 6.12.0-55.50.1.el10_0, kernel-debuginfo-common-x86_64 6.12.0-55.50.1.el10_0, kernel-debuginfo-common-aarch64 6.12.0-55.50.1.el10_0, kernel-debuginfo-common-ppc64le 6.12.0-55.50.1.el10_0
    fixed: vendor fix RHSA-2025:23250
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-611.16.1.el9_7, kernel-rt-64k 5.14.0-611.16.1.el9_7, kernel-rt-core 5.14.0-611.16.1.el9_7, kernel-rt-modules 5.14.0-611.16.1.el9_7, kernel-rt-64k-core 5.14.0-611.16.1.el9_7, kernel-rt-debug-core 5.14.0-611.16.1.el9_7, +14 more
    fixed: vendor fix RHSA-2025:23241
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-124.27.1.el10_1, kernel-rt-64k 6.12.0-124.27.1.el10_1, kernel-rt-core 6.12.0-124.27.1.el10_1, kernel-rt-modules 6.12.0-124.27.1.el10_1, kernel-rt-64k-core 6.12.0-124.27.1.el10_1, kernel-rt-debug-core 6.12.0-124.27.1.el10_1, +14 more
    fixed: vendor fix RHSA-2026:0453
  • Red Hat Enterprise Linux Real Time EUS (v. 10.0) kernel-rt 6.12.0-55.50.1.el10_0, kernel-rt-64k 6.12.0-55.50.1.el10_0, kernel-rt-core 6.12.0-55.50.1.el10_0, kernel-rt-modules 6.12.0-55.50.1.el10_0, kernel-rt-64k-core 6.12.0-55.50.1.el10_0, kernel-rt-debug-core 6.12.0-55.50.1.el10_0, +14 more
    fixed: vendor fix RHSA-2025:23250
  • Red Hat Enterprise Linux Real Time EUS (v.9.6) kernel-rt 5.14.0-570.72.1.el9_6, kernel-rt-64k 5.14.0-570.72.1.el9_6, kernel-rt-core 5.14.0-570.72.1.el9_6, kernel-rt-modules 5.14.0-570.72.1.el9_6, kernel-rt-64k-core 5.14.0-570.72.1.el9_6, kernel-rt-debug-core 5.14.0-570.72.1.el9_6, +14 more
    fixed: vendor fix RHSA-2025:22802
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-611.16.1.el9_7, kernel-rt-core 5.14.0-611.16.1.el9_7, kernel-rt-modules 5.14.0-611.16.1.el9_7, kernel-rt-debug-core 5.14.0-611.16.1.el9_7, kernel-rt-modules-core 5.14.0-611.16.1.el9_7, kernel-rt-debug-modules 5.14.0-611.16.1.el9_7, +4 more
    fixed: vendor fix RHSA-2025:23241
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-124.27.1.el10_1, kernel-rt-core 6.12.0-124.27.1.el10_1, kernel-rt-modules 6.12.0-124.27.1.el10_1, kernel-rt-debug-core 6.12.0-124.27.1.el10_1, kernel-rt-modules-core 6.12.0-124.27.1.el10_1, kernel-rt-debug-modules 6.12.0-124.27.1.el10_1, +4 more
    fixed: vendor fix RHSA-2026:0453
  • Red Hat Enterprise Linux Real Time for NFV EUS (v. 10.0) kernel-rt 6.12.0-55.50.1.el10_0, kernel-rt-kvm 6.12.0-55.50.1.el10_0, kernel-rt-core 6.12.0-55.50.1.el10_0, kernel-rt-modules 6.12.0-55.50.1.el10_0, kernel-rt-debug-kvm 6.12.0-55.50.1.el10_0, kernel-rt-debug-core 6.12.0-55.50.1.el10_0, +6 more
    fixed: vendor fix RHSA-2025:23250
  • Red Hat Enterprise Linux Real Time for NFV EUS (v.9.6) kernel-rt 5.14.0-570.72.1.el9_6, kernel-rt-kvm 5.14.0-570.72.1.el9_6, kernel-rt-core 5.14.0-570.72.1.el9_6, kernel-rt-modules 5.14.0-570.72.1.el9_6, kernel-rt-debug-kvm 5.14.0-570.72.1.el9_6, kernel-rt-debug-core 5.14.0-570.72.1.el9_6, +6 more
    fixed: vendor fix RHSA-2025:22802
  • 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
    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

0.11% chance of exploitation in the next 30 days, higher than 1% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 7.0 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Linux Linux

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization
Technology feeds

References

Sources

Fencer Intel 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.