[CVE-2026-89556][LOW] module: validate string table section types

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-89556
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: module: validate string table section types
Commit: 50d0aa7d25ba4bc3606f150cd69755068e79f97f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=50d0aa7d25ba4bc3606f150cd69755068e79f97f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89556
Analysis date: Fri, 11 Sep 2026 16:50:56 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89556 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89556

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-2026-89556	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89556 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H';CWE-125;*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: '5.1';DESCR 'The module loader could access out of bounds memory while validating a malformed ELF module because the section name string table or symbol string table could have type SHT_NULL or SHT_NOBITS instead of SHT_STRTAB. In that case sh_offset may not have been validated before later string table access, which can cause an invalid kernel read during module loading. For the CVSS the PR:H is used because reliable triggering normally requires the ability to load an arbitrary kernel module through init_module or finit_module, which is restricted to root or CAP_SYS_MODULE. The issue is not network reachable and is triggered through the local module loading interface. Impact is mainly denial of service via kernel oops or panic. The paranoid score adds limited confidentiality impact for the invalid read class, but there is no clear write primitive or UAF path indicating privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	WRITE OOB SIMPLEFIX LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	guess

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

ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

2. Signal breakdown

Positive signals:

* +1 Weak internal invalid read / OOB read candidate. The module loader may use an unvalidated sh_offset from a section with type SHT_NULL or SHT_NOBITS when later accessing ELF string table data.
* +1 Possible kernel crash / DoS. Invalid kernel memory access during malformed module validation may plausibly cause an oops or panic.

Negative signals:

* -2 Host-admin-equivalent privilege required. Triggering requires loading a crafted kernel module through the module loading path, which normally requires host root or CAP_SYS_MODULE.

Non-awarded signals:

* No RealUAF. No stale object or post-lifetime use is established.
* No concrete write primitive. The patch supports an invalid read, not OOB write, arbitrary write, refcount corruption, or object replacement.
* No confidentiality bonus. The OOB read is internal to validation and no user-visible disclosure path is established.
* No integrity bonus. No unauthorized modification of kernel state or protected data is shown.
* No remote reachability. The vulnerable operation is local module loading.
* No structured stale-object leverage. There is no stale object.
* No repeated release/refcount operation. No first release, surviving dangling reference, or second lifetime mutation exists.
* No extra availability point. The same possible crash is already counted once.

3. Reachability analysis

The trigger is a malformed ELF kernel module supplied to the kernel module loader. Reliable triggering normally requires the ability to call init_module or finit_module with arbitrary module contents. That is host-admin-equivalent in normal Linux deployments because it requires CAP_SYS_MODULE or root-level control.

This is not namespace-scoped in a way that helps an ordinary attacker. The supplied evidence does not show an attacker-created namespace where the complete module loading operation is available below host admin. There is no network path and no packet-processing trigger. No special hardware, firmware, race, or timing condition is required beyond access to the module loading interface.

4. Primitive and severity interpretation

The exact primitive is a validation failure in the module ELF parser that can lead to an internal out-of-bounds read from an unvalidated section offset. This is not an active structured UAF, not fixed stale storage, and not a cleanup/destructor lifetime bug. There is no concrete repeated release/refcount operation.

PrimitiveClass is CLASS_C because the demonstrated behavior is an invalid read / crash-style condition without an independently useful corruption, disclosure, ownership, or authorization primitive. The demonstrated consequence is local DoS against the host kernel by a host-admin-equivalent actor. A stronger consequence such as privilege escalation is speculative and not supported by the patch mechanics.

ImportantCandidate=NO because the path is host-admin gated and the primitive is not strong enough to preserve Important severity. AutoDowngradeAllowed=YES because no unresolved memory corruption, lifetime mutation, authorization bypass, or security-boundary primitive remains.

Likely operational severity is ordinary Moderate / Low-like, and it is suitable for deferred or automatic handling in most environments.

5. One-sentence report phrase

A malformed kernel module can cause the module loader to perform an internal out-of-bounds read while validating ELF string table sections, but exploitation normally requires host-admin module loading privileges and the supported impact is local kernel DoS only.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: host-admin-equivalent module loading is required, and the established primitive is an internal invalid read / possible crash without UAF, write corruption, disclosure, authorization bypass, or LPE evidence.

7. Call-site confidence

Call-site confidence: high

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

Patch: module: validate string table section types
Commit: 50d0aa7d25ba4bc3606f150cd69755068e79f97f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=50d0aa7d25ba4bc3606f150cd69755068e79f97f

Commit description:

In elf_validity_cache_sechdrs, section sizes and offsets are validated,
unless the section type is SHT_NULL or SHT_NOBITS.

Later, elf_validity_cache_secstrings and elf_validity_cache_index_str
access the section name table (.shstrtab) and symbol string table
(.strtab) headers without first ensuring that their types are
SHT_STRTAB. If a section type is SHT_NULL or SHT_NOBITS, sh_offset has
not been validated and may reference out-of-bounds memory when
dereferenced in elf_validity_cache_secstrings or
elf_validity_cache_strtab.

Validate that both string section headers are of type SHT_STRTAB before
caching them.

Cc: stable@vger.kernel.org
Signed-off-by: Thiébaud Weksteen <tweek@google.com>
Reviewed-by: Aaron Tomlin <atomlin@atomlin.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/module/main.c

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=50d0aa7d25ba4bc3606f150cd69755068e79f97f

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

The original Linux kernel CVE announcement for CVE-2026-89556 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89556

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:H/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 5.1

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: unknown
  Paranoid ActionableScore: 0

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).