[CVE-2026-93055][MODERATE REGULAR] UDF symlink pathComponent header OOB read [ Upstream

[CVE-2026-93055][MODERATE REGULAR] UDF symlink pathComponent header OOB read [ Upstream

[AL-KERNEL]

CVE: CVE-2026-93055
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: UDF symlink pathComponent header OOB read [ Upstream
Commit: d9f49c8b55debf1512f912077b6c759cc8b6d2e0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d9f49c8b55debf1512f912077b6c759cc8b6d2e0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93055
Analysis date: Thu, 17 Sep 2026 23:47:17 -0400
ActionableScore: 3
ActionableScore lower bound: 2
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-2026-93055 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93055

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-2026-93055	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-93055 CHECK WITH IMPACT FROM ORIG NN MODERATE	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:N/A:H';CWE-125;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '6.1';DESCR 'A malformed UDF symlink can make udf_pc_to_char parse a partial pathComponent header and read past the end of the symlink input buffer. The trigger is a crafted UDF filesystem image or media containing malformed symlink data that is later parsed by the kernel. For the CVSS the PR:L is used because a local user or automount capable desktop session may be able to cause the kernel to parse the crafted UDF content, while fully manual root only mounting would reduce practical exposure. The issue is not directly network reachable and is tied to local filesystem or removable media handling. Impact is at least local denial of service or read failure, and in the paranoid interpretation may include limited confidentiality impact from an out of bounds read plus high availability impact from a kernel crash. It should not be treated as proven privilege escalation because the patch shows an invalid read, not a write primitive or UAF.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)  SKIP CVE-2026-93055 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	OOB DISK SIMPLEFIX LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2. No floor or cap applied.
* Raw paranoid score: 3
* Paranoid score: 3. No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative signals:

* +1 Limited OOB read / invalid structured header read. The patch directly shows that `udf_pc_to_char()` could read a `struct pathComponent` header when fewer than `sizeof(struct pathComponent)` bytes remain.
* +1 Attacker-influenced filesystem parser input. The malformed data is symlink content from a crafted UDF filesystem image or media, so attacker-controlled on-disk data can reach a kernel parser once the filesystem is mounted or automounted.

Paranoid-only signal:

* +1 Possible local DoS / crash concern. A kernel OOB read in a filesystem parser can plausibly lead to a fault, KASAN report, or symlink resolution failure depending on allocation/layout, but this is not enough to infer memory corruption beyond the read.

Non-awarded signals:

* RealUAF not awarded. No freed object or stale lifetime use is shown.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Strong LPE leverage not demonstrated.
* Confidentiality not awarded. The patch shows an internal OOB read, but no clear path that out-of-bounds bytes are copied to userspace, network, or another attacker-visible sink.
* Integrity not awarded. There is no write primitive or ownership/COW/security-boundary violation.
* Remote reachability not established. This is a local filesystem/media parsing issue, not packet-triggered network input.
* Extra availability not awarded beyond the paranoid crash concern.

3. Reachability analysis

The likely trigger is a malformed UDF filesystem containing a symlink whose path data ends with a partial `pathComponent` header. The vulnerable path is reached when the kernel resolves or reads that symlink after the UDF image/media is mounted.

Host-admin-equivalent privilege is not positively established as always required, because desktop automount or privileged helper configurations may allow a local user to cause removable UDF media to be mounted and parsed. However, below-host-admin reachability is also not fully proven by the supplied patch alone, because manual mounting of arbitrary filesystem images normally requires privileged help. Therefore `HostAdminRequired=UNKNOWN`.

No namespace-scoped capability chain is involved. No network trigger is established. No special rare hardware is required beyond UDF media/image handling. No race or timing condition is involved.

4. Primitive and severity interpretation

The exact primitive is a read-only out-of-bounds access of a partial `struct pathComponent` header in `udf_pc_to_char()`. This is not an active structured UAF and not fixed stale storage. It is a malformed filesystem parser input issue.

Primitive class is `CLASS_C` because the demonstrated behavior is an invalid/OOB read with likely crash or error-path consequences, but without an independently useful corruption, disclosure, ownership, or authorization primitive.

The demonstrated consequence is malformed UDF symlink parsing causing an internal OOB read. The speculative consequence is local DoS if the read crosses an invalid boundary or triggers hardening/debug checks. Exploitation beyond DoS is not supported by the patch.

`ImportantCandidate=NO` because there is no UAF, no write primitive, no controlled replacement, no shared-page ownership violation, and no authorization bypass. `AutoDowngradeAllowed=YES` because the unresolved primitive is limited and does not establish meaningful Important-grade exploitation leverage.

Likely operational severity is ordinary to borderline Moderate, with manual review useful mainly to confirm whether the OOB bytes can ever influence user-visible symlink output or cause reliable production crashes.

5. One-sentence report phrase

A crafted UDF symlink with a partial pathComponent header can make the kernel UDF parser perform a limited out-of-bounds read during symlink resolution, with practical impact most likely limited to local denial of service or parse failure.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a kernel filesystem parser OOB read from attacker-controlled on-disk data, but the patch does not show UAF, write corruption, disclosure, or privilege escalation.

7. Call-site confidence

Call-site confidence: medium

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

Patch: UDF symlink pathComponent header OOB read [ Upstream
Commit: d9f49c8b55debf1512f912077b6c759cc8b6d2e0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d9f49c8b55debf1512f912077b6c759cc8b6d2e0

Changed files:
  fs/udf/symlink.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=d9f49c8b55debf1512f912077b6c759cc8b6d2e0

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

The original Linux kernel CVE announcement for CVE-2026-93055 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93055

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:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 6.1

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: 2
  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).