[CVE-2026-89525][MODERATE REGULAR] udf: reject VAT indexes equal to the entry count

[CVE-2026-89525][MODERATE REGULAR] udf: reject VAT indexes equal to the entry count

[AL-KERNEL]

CVE: CVE-2026-89525
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: udf: reject VAT indexes equal to the entry count
Commit: 9193368408d792cec2057628d87862140fb1ce1c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9193368408d792cec2057628d87862140fb1ce1c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89525
Analysis date: Sat, 12 Sep 2026 05:23:45 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89525 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89525

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: MODERATE REGULAR
Manual review required: YES

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

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

CVE-2026-89525	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89525 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:L/UI:N/S:U/C:L/I:L/A:H';CWE-193;CWE-125;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '6.6';DESCR 'A one entry out of bounds read in the UDF 1.50 VAT mapping path occurs because udf_get_pblock_virt15 treated s_num_entries as an inclusive maximum instead of an exclusive entry count. A crafted UDF image can request VAT index s_num_entries and make the kernel read past the allocated VAT table, with KASAN showing a slab out of bounds report and a reproducible kernel panic. For the CVSS the PR:L value is used for the paranoid score because a local user may be able to trigger filesystem parsing through allowed media or image mounting paths, while direct mount on hardened servers may require administrator rights. The issue is not directly network reachable and requires a crafted local filesystem image or media. Impact is at least denial of service via kernel crash, with limited confidentiality or integrity impact possible in the worst case because the primitive is an out of bounds read used for block translation rather than an arbitrary write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)  SKIP CVE-2026-89525 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	KASAN OOB DISK SIMPLEFIX IMPROVEONLY LINUS  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::

No floor or cap changed the score.

2. Signal breakdown

Positive signals:

* +1 Limited OOB read / unchecked index: the patch fixes an off-by-one bounds check where VAT index s_num_entries was incorrectly accepted.
* +1 Reliable kernel crash / strong DoS: supplied evidence says a crafted UDF image triggers KASAN slab-out-of-bounds and kernel panic.
* +1 Important filesystem/storage path: the invalid value is in filesystem block translation logic for UDF virtual partition mapping.

Non-awarded or withheld signals:

* RealUAF not awarded: no freed object or post-lifetime stale reference is established.
* Class A not awarded: no controlled write, controlled reclaim, callback control, ownership/COW violation, authorization bypass, or demonstrated LPE.
* Class B not awarded: the established primitive is a one-entry read past an allocated VAT table with crash evidence, not a lifetime or active-object corruption primitive.
* Confidentiality not awarded: the patch shows an internal kernel OOB read, but no user-visible disclosure path is established.
* Integrity not awarded: the read value may affect block translation, but no unauthorized write to protected data or filesystem ownership violation is established.
* Local unprivileged trigger not awarded: user-triggerable parsing through automount or delegated mount helpers is plausible in some deployments, but the complete below-host-admin path is not established by the supplied evidence.
* Remote reachability not awarded: this requires a crafted local filesystem image or media, not network traffic.
* Extra availability point not awarded: the kernel panic is already counted as the DoS signal.

3. Reachability analysis

The attacker needs to supply a crafted UDF 1.50 image or media and cause the kernel UDF parser to process it. Direct mounting usually requires CAP_SYS_ADMIN or equivalent mount authority, but desktop automount, removable-media workflows, sandboxed mount helpers, or delegated storage services may reduce the practical privilege requirement in some environments. The supplied evidence does not prove the complete trigger is available to an ordinary unprivileged local user, so HostAdminRequired remains UNKNOWN rather than YES or NO.

No namespace-scoped capability path is established. No network vector is established. No special rare hardware is required. This is not a race.

4. Primitive and severity interpretation

The exact primitive is an off-by-one read in udf_get_pblock_virt15(). The code treated s_num_entries as the highest valid VAT index, but it is actually the number of entries, so valid indexes are below s_num_entries. A crafted image can request index s_num_entries and read one entry past the allocated VAT table.

This is a read-only OOB access with demonstrated crash behavior. It is not a UAF, not a double release, not an OOB write, and not an authorization bypass. The demonstrated consequence is kernel panic / local DoS. A stronger confidentiality or integrity consequence is theoretically possible only if later analysis finds a concrete disclosure path or a block-translation effect that crosses a protected ownership boundary, but that is not established here.

PrimitiveClass=CLASS_C because the established behavior is primarily invalid memory read and crash. ImportantCandidate=NO because no meaningful exploitation leverage beyond crash is currently established. AutoDowngradeAllowed=YES because this can be treated as ordinary or borderline Moderate after review, unless additional advisory evidence shows unprivileged reachability or a concrete C/I consequence.

5. One-sentence report phrase

A crafted UDF 1.50 image can trigger an off-by-one VAT index lookup in udf_get_pblock_virt15(), causing a one-entry slab out-of-bounds read and a reproducible kernel panic.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a crafted filesystem parser memory-safety issue with KASAN panic evidence, but current evidence supports DoS only and does not establish UAF, write corruption, disclosure, or privilege escalation.

7. Call-site confidence

Call-site confidence: medium

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

Patch: udf: reject VAT indexes equal to the entry count
Commit: 9193368408d792cec2057628d87862140fb1ce1c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9193368408d792cec2057628d87862140fb1ce1c

Commit description:

UDF 1.50 virtual partition mapping uses the VAT as an array of physical
block mappings. s_num_entries stores the number of entries in that array,
not the highest valid index. The valid VAT indexes are therefore below
s_num_entries.

udf_get_pblock_virt15() currently rejects only indexes greater than
s_num_entries. A crafted image can request index s_num_entries, pass the
bounds check, and make the kernel read one entry past the allocated VAT table.

Change the check to reject block >= s_num_entries, so the count is handled as
an exclusive upper bound.

A crafted UDF image reproduced this on origin/master commit
0e35b9b with a KASAN slab-out-of-bounds
report in udf_get_pblock_virt15().

Trail of Bits has a reproducer that triggers kernel panic demonstrating the bug, and can share it if needed.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: David Lee <david.lee@trailofbits.com>
Assisted-by: Codex:gpt-5.5
Link: https://patch.msgid.link/20260708101712.1706564-1-david.lee@trailofbits.com
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/udf/partition.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=9193368408d792cec2057628d87862140fb1ce1c

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

The original Linux kernel CVE announcement for CVE-2026-89525 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89525

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:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.6

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: 3

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: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).