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Fencer Vulns
critical 9.8

CVE-2026-63808 in the critical feed json

exfat: fix potential use-after-free in exfat_find_dir_entry()

published 2026-07-19 3 mo ago modified 2026-10-22 17 d ago also EUVD-2026-45474

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:

exfat: fix potential use-after-free in exfat_find_dir_entry()

In exfat_find_dir_entry(), the buffer_head obtained from exfat_get_dentry() is released with brelse(bh) before the fall-through TYPE_EXTEND branch reads the directory entry through ep (which points into bh->b_data):

brelse(bh); if (entry_type == TYPE_EXTEND) { ... len = exfat_extract_uni_name(ep, entry_uniname); ... }

After brelse() drops our reference, nothing guarantees that the underlying page backing bh->b_data remains valid for the subsequent exfat_extract_uni_name() read. This is the same pattern fixed in commit fc961522ddbd ("exfat: Fix potential use after free in exfat_load_upcase_table()").

Move brelse(bh) so it runs after ep is no longer dereferenced on each branch.

Confirmed on QEMU x86_64 with CONFIG_KASAN=y + CONFIG_DEBUG_PAGEALLOC=y + CONFIG_PAGE_POISONING=y on linux-next, using a crafted exFAT image (long filename with same-hash collisions forcing the TYPE_EXTEND path). With a debug-only invalidate_bdev() inserted between brelse(bh) and the ep read to make the stale-deref window deterministic, the unpatched kernel faults:

BUG: KASAN: use-after-free in exfat_find_dir_entry+0x133b/0x15a0 BUG: unable to handle page fault for address: ffff88801a5fa0c2 Oops: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI RIP: 0010:exfat_find_dir_entry+0x1188/0x15a0

With this patch applied, the same instrumented harness completes cleanly under the same sanitizer stack. I have not reproduced a crash on an uninstrumented kernel under ordinary reclaim; the instrumented A/B establishes the lifetime violation and that the patch closes it, not an unaided triggerability claim.

Patch / fix

  • Linux Linux 5.10.260, 5.15.211, 6.1.177, 6.6.144, 6.12.95, 6.18.38, 7.1.3, 7.2
  • linux Debian 12 6.1.177-1
  • linux Debian 13 6.12.95-1
  • linux Debian 14 7.1.3-1

debian advisories DEBIAN-CVE-2026-63808

  • linux Ubuntu 22.04 LTS 5.15.0-194.204
  • linux Ubuntu 24.04 LTS 6.8.0-147.147
  • linux Ubuntu 26.04 LTS 7.0.0-31.31
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1116.123
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1067.70
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1012.12
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1117.127
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1071.79

ubuntu advisories UBUNTU-CVE-2026-63808

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 10.2 6.12.0-211.51.1.el10_2
  • rv RHEL 10.2 6.12.0-211.51.1.el10_2
  • perf RHEL 10.2 6.12.0-211.51.1.el10_2
  • rtla RHEL 10.2 6.12.0-211.51.1.el10_2
  • libperf RHEL 10.2 6.12.0-211.51.1.el10_2
  • kernel-rt RHEL 10.2 6.12.0-211.51.1.el10_2
  • kernel-64k RHEL 10.2 6.12.0-211.51.1.el10_2
  • kernel-core RHEL 10.2 6.12.0-211.51.1.el10_2

red hat advisories RHSA-2026:63128RHSA-2026:63129

  • kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.81.1
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.81.1
  • kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.53.81.1
  • kernel-source SLE Module for Development Tools 15 SP7, SLE Module for Basesystem 15 SP7 6.4.0-150700.53.81.1
  • kernel-default SLE Workstation Extension 15 SP7, SLE Module for Legacy 15 SP7, SLE Module for Basesystem 15 SP7 +2 more 6.4.0-150700.53.81.1
  • kernel-zfcpdump SLE Module for Basesystem 15 SP7 6.4.0-150700.53.81.1
  • kernel-obs-build SLE Module for Development Tools 15 SP7 6.4.0-150700.53.81.1
  • kernel-default-base SLE Module for Basesystem 15 SP7 6.4.0-150700.53.81.1.150700.17.45.1

suse advisories SUSE-SU-2026:4254-1SUSE-SU-2026:23887-1SUSE-SU-2026:23902-1SUSE-SU-2026:23897-1SUSE-SU-2026:23881-1SUSE-SU-2026:4120-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.38.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.38.1

opensuse advisories openSUSE-SU-2026:21910-1openSUSE-SU-2026:11339-1

  • kernel AlmaLinux 10 6.12.0-211.51.1.el10_2
  • rv AlmaLinux 10 6.12.0-211.51.1.el10_2
  • perf AlmaLinux 10 6.12.0-211.51.1.el10_2
  • rtla AlmaLinux 10 6.12.0-211.51.1.el10_2
  • libperf AlmaLinux 10 6.12.0-211.51.1.el10_2
  • kernel-rt AlmaLinux 10 6.12.0-211.51.1.el10_2
  • kernel-64k AlmaLinux 10 6.12.0-211.51.1.el10_2
  • kernel-core AlmaLinux 10 6.12.0-211.51.1.el10_2

almalinux advisories ALSA-2026:63128ALSA-2026:63129

  • kernel Rocky Linux 10 6.12.0-211.51.1.el10_2
  • kernel Rocky Linux 9 5.14.0-687.44.1.el9_8

rocky linux advisories RLSA-2026:63128RLSA-2026:63129

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-2026-63808 updated cvss 4.7

kernel: exfat: fix potential use-after-free in exfat_find_dir_entry()

  • 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 Enterprise Linux AppStream (v. 9) rv 5.14.0-687.44.1.el9_8, perf 5.14.0-687.44.1.el9_8, rtla 5.14.0-687.44.1.el9_8, python3-perf 5.14.0-687.44.1.el9_8, kernel-devel-matched 5.14.0-687.44.1.el9_8, kernel-64k-devel-matched 5.14.0-687.44.1.el9_8, +7 more
    fixed: vendor fix RHSA-2026:63129
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-211.51.1.el10_2, perf 6.12.0-211.51.1.el10_2, rtla 6.12.0-211.51.1.el10_2, python3-perf 6.12.0-211.51.1.el10_2, kernel-devel-matched 6.12.0-211.51.1.el10_2, kernel-64k-devel-matched 6.12.0-211.51.1.el10_2, +7 more
    fixed: vendor fix RHSA-2026:63128
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-687.44.1.el9_8, kernel-64k 5.14.0-687.44.1.el9_8, kernel-core 5.14.0-687.44.1.el9_8, kernel-tools 5.14.0-687.44.1.el9_8, kernel-modules 5.14.0-687.44.1.el9_8, kernel-64k-core 5.14.0-687.44.1.el9_8, +27 more
    fixed: vendor fix RHSA-2026:63129
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-211.51.1.el10_2, kernel-64k 6.12.0-211.51.1.el10_2, kernel-core 6.12.0-211.51.1.el10_2, kernel-tools 6.12.0-211.51.1.el10_2, kernel-modules 6.12.0-211.51.1.el10_2, kernel-64k-core 6.12.0-211.51.1.el10_2, +28 more
    fixed: vendor fix RHSA-2026:63128
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-687.44.1.el9_8, kernel-debuginfo-common-s390x 5.14.0-687.44.1.el9_8, kernel-debuginfo-common-x86_64 5.14.0-687.44.1.el9_8, kernel-debuginfo-common-aarch64 5.14.0-687.44.1.el9_8, kernel-debuginfo-common-ppc64le 5.14.0-687.44.1.el9_8
    fixed: vendor fix RHSA-2026:63129
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-211.51.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.51.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.51.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.51.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.51.1.el10_2
    fixed: vendor fix RHSA-2026:63128
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-687.44.1.el9_8, kernel-rt-64k 5.14.0-687.44.1.el9_8, kernel-rt-core 5.14.0-687.44.1.el9_8, kernel-rt-modules 5.14.0-687.44.1.el9_8, kernel-rt-64k-core 5.14.0-687.44.1.el9_8, kernel-rt-debug-core 5.14.0-687.44.1.el9_8, +14 more
    fixed: vendor fix RHSA-2026:63129
show 4 more
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-211.51.1.el10_2, kernel-rt-64k 6.12.0-211.51.1.el10_2, kernel-rt-core 6.12.0-211.51.1.el10_2, kernel-rt-modules 6.12.0-211.51.1.el10_2, kernel-rt-64k-core 6.12.0-211.51.1.el10_2, kernel-rt-debug-core 6.12.0-211.51.1.el10_2, +14 more
    fixed: vendor fix RHSA-2026:63128
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-687.44.1.el9_8, kernel-rt-core 5.14.0-687.44.1.el9_8, kernel-rt-modules 5.14.0-687.44.1.el9_8, kernel-rt-debug-core 5.14.0-687.44.1.el9_8, kernel-rt-modules-core 5.14.0-687.44.1.el9_8, kernel-rt-debug-modules 5.14.0-687.44.1.el9_8, +4 more
    fixed: vendor fix RHSA-2026:63129
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-211.51.1.el10_2, kernel-rt-core 6.12.0-211.51.1.el10_2, kernel-rt-modules 6.12.0-211.51.1.el10_2, kernel-rt-debug-core 6.12.0-211.51.1.el10_2, kernel-rt-modules-core 6.12.0-211.51.1.el10_2, kernel-rt-debug-modules 6.12.0-211.51.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:63128
  • 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

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
total
Assessed
23 d ago

Exploit prediction

0.53% 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.