[CVE-2026-74426][LOW] afs: fix NULL pointer dereference in afs_get_tree()

[CVE-2026-74426][LOW] afs: fix NULL pointer dereference in afs_get_tree()

[AL-KERNEL]

CVE: CVE-2026-74426
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: afs: fix NULL pointer dereference in afs_get_tree()
Commit: 67fb48c4a0874953212321cd5d57fdb4900dbc31
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=67fb48c4a0874953212321cd5d57fdb4900dbc31
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74426
Analysis date: Sat, 15 Aug 2026 03:35:44 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like. Not Actionable Moderate
Manual review required: NO

Summary:
A local NULL pointer dereference in the AFS dynamic-root mount path can crash the kernel when AFS tracepoint handling dereferences uninitialized cell or volume pointers, but exploitation typically requires privileged mount and tracing access.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-74426 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74426

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-74426	LOW	CHECK WITH IMPACT FROM ORIG NN NONE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference can occur in the AFS mount path because afs_get_tree() calls trace_afs_get_tree() even for a dynamic root mount where the cell and volume pointers are not initialized. A local actor can trigger the crash through the mount path when AFS tracing or perf tracepoint handling dereferences those NULL pointers. For the CVSS the PR:L is used in the paranoid score because some deployments may delegate mount or tracing capability to a reduced privilege service, container root, or local administrative helper rather than full host root. The issue is not directly network reachable because the failing path is local mount and tracing control logic, not remote AFS packet handling. Impact is denial of service via kernel crash, with no supported evidence of confidentiality impact, integrity impact, UAF, OOB write, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like. Not Actionable Moderate (with actual score 1)	YES	KASAN NULLPTR DISK SKIP HARDWARE  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like. Not Actionable Moderate**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1. The patch and KASAN trace show a NULL pointer dereference in `perf_trace_afs_get_tree()`.
* Requires admin/root/CAP_SYS_ADMIN or tracing privileges in typical deployments: -2. Triggering the mount path normally requires mount privileges, and the failing tracepoint path generally requires tracing or perf tracepoint enablement.
* Rare AND difficult-to-reach subsystem/configuration: -1. AFS dynamic-root mount plus active AFS tracepoint handling is not a common default exposure.
* Score floored to 0.

Paranoid adjustment:

* Reduced-privilege delegated environment considered: penalty relaxed from -2 to 0 or -1 in environments where a container root, service helper, or delegated mount/tracing capability can reach the path.
* Paranoid score remains only 1 because the primitive is still a NULL dereference, not UAF, OOB write, type confusion, refcount misuse, or object lifetime corruption.

No awarded signals:

* No remote/network-triggerable signal. The failing path is local mount/tracing logic, not AFS packet processing.
* No generic memory corruption signal. The evidence is NULL pointer dereference only.
* No privilege escalation plausible signal. No reclaim, overwrite, callback control, object confusion, or write primitive is shown.
* No confidentiality or integrity impact. No disclosure or unauthorized modification primitive is supported.

## 3. Reachability analysis

The realistic trigger is local and privileged: a process must reach the AFS mount path for a dynamic root and have the relevant tracepoint/perf path active. In normal deployments this requires administrative mount/tracing privileges, usually CAP_SYS_ADMIN or equivalent. Namespaces or containers could lower the practical privilege boundary only if mount or tracing capability is delegated, but that is environment-specific. AFS is not a broad default filesystem exposure, and this is not reachable by remote AFS traffic alone.

Call-site confidence: high. The provided trace and patch show the direct call from `afs_get_tree()` to `trace_afs_get_tree()` and the exact NULL fields avoided by the fix.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like kernel DoS issue. The theoretical impact is a local kernel crash through a NULL pointer dereference. Realistic exploitation evidence does not support privilege escalation, memory corruption beyond NULL dereference, information disclosure, or integrity compromise. The issue is suitable for non-urgent handling unless the product enables AFS dynamic-root mounts and tracing paths for less privileged users.

## 5. One-sentence report phrase

A local NULL pointer dereference in the AFS dynamic-root mount path can crash the kernel when AFS tracepoint handling dereferences uninitialized cell or volume pointers, but exploitation typically requires privileged mount and tracing access.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a clearly bounded NULL pointer dereference DoS with privileged local reachability and no supported memory corruption, LPE, confidentiality, or integrity primitive.

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: afs: fix NULL pointer dereference in afs_get_tree()
Commit: 67fb48c4a0874953212321cd5d57fdb4900dbc31
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=67fb48c4a0874953212321cd5d57fdb4900dbc31

Commit description:

afs_alloc_sbi() uses kzalloc for memory allocation. And, if
ctx->dyn_root is not null, as->cell and as->volume are null.
In trace_afs_get_tree() they are dereferenced.

KASAN error message:

KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 2 PID: 18478 Comm: syz-executor.7 Not tainted 5.10.246-syzkaller #0
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1
04/01/2014
RIP: 0010:perf_trace_afs_get_tree+0x1d9/0x550
include/trace/events/afs.h:1365

Call Trace:
trace_afs_get_tree include/trace/events/afs.h:1365 [inline]
afs_get_tree+0x922/0x1350 fs/afs/super.c:599
vfs_get_tree+0x8e/0x300 fs/super.c:1572
do_new_mount fs/namespace.c:3011 [inline]
path_mount+0x14a5/0x2220 fs/namespace.c:3341
do_mount fs/namespace.c:3354 [inline]
__do_sys_mount fs/namespace.c:3562 [inline]
__se_sys_mount fs/namespace.c:3539 [inline]
__x64_sys_mount+0x283/0x300 fs/namespace.c:3539
 do_syscall_64+0x33/0x50 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x67/0xd1

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 80548b0 ("afs: Add more tracepoints")
Cc: stable@vger.kernel.org
Signed-off-by: Matvey Kovalev <matvey.kovalev@ispras.ru>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260622090856.2746629-4-dhowells@redhat.com
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  include/trace/events/afs.h:1365

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=67fb48c4a0874953212321cd5d57fdb4900dbc31

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-74426 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74426

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 0
  Paranoid ActionableScore: 1

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).