[CVE-2026-99185][IMPORTANT] firewire: core: fix race condition in split transaction handling [ Upstream

[CVE-2026-99185][IMPORTANT] firewire: core: fix race condition in split transaction handling [ Upstream

[AL-KERNEL]

CVE: CVE-2026-99185
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: firewire: core: fix race condition in split transaction handling [ Upstream
Commit: a8caee0e623ca5d56e829032f9ec073c09e4d224
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a8caee0e623ca5d56e829032f9ec073c09e4d224
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99185
Analysis date: Fri, 30 Oct 2026 12:05:06 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A malicious FireWire device can race a split response against timeout handling, causing duplicate transaction processing and an initiator-side UAF with plausible kernel crash impact.

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

The original Linux kernel CVE announcement for CVE-2026-99185 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99185

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: IMPORTANT
Manual review required: YES

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

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-99185	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-99185 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;CWE-367;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A race between fw_core_handle_response and split_transaction_timeout_callback can allow both paths to process the same pending split transaction when timer_delete returns zero. The first completion callback may release the initiator object while the competing path still holds and uses the transaction entry, creating an initiator side use after free with likely kernel crash impact and a possible memory corruption consequence. Exploitation requires a split transaction and precise response timing against the timeout callback, so AC:H is appropriate. For the CVSS the PR:N value reflects that a malicious device on the directly attached FireWire bus does not need a local account, while AV:A reflects physical or adjacent bus access rather than ordinary network reachability. The base score uses C:L and I:L because a concrete UAF exists but no controlled read or write primitive is established. The paranoid score uses C:H I:H A:H because reuse of the freed kernel object may have broader effects and requires manual source level validation. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 7.5 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage IMPORTANT to IMPORTANT because KP specialist did not establish a qualifying panic. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were TEMP_KPANIC_MERGE_IMPORTANT_WINS and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 3.1 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	RACE LEAK UAF LINUS TEMP_KPANIC_MERGE_IMPORTANT_WINS KPANIC_UNSUPPORTED_REMOVED	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 0.
* Conservative score: 4. REAL UAF FLOOR 4 applied: 0 -> 4.
* Raw paranoid score: 0.
* Paranoid score: 4. No additional exploit primitive supports a paranoid increment.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 — Real UAF: failed timer cancellation means the running timeout callback retains responsibility, but the vulnerable response path can also process the same transaction.
* +1 — Plausible kernel crash: concurrent processing can use initiator state after the first completion releases it.
* -1 — Hard timing: the malicious device must align a split response with an already-running timeout callback.
* -2 — Physical/special hardware exposure: the supported attacker model requires access to a directly attached FireWire bus/device.
* No repeated-release point: the supplied diff does not show two specific puts, frees, or refcount mutations on the exact reference.
* No structured-leverage, controlled-reclaim, arbitrary-write, disclosure, or C/I point is proven. The paranoid CVSS consequences do not establish these primitives.
* No extra availability point: it would duplicate the same possible crash.
* NEW52/B5-R, B3-PENDING, and B4-PENDING do not apply.

3. Reachability analysis

A malicious attached FireWire device can influence split-response timing without a host account, host UID 0, or namespace capability. The host must initiate a split transaction, and precise timeout overlap is required. No ordinary network or local-userspace trigger is shown. The complete path is hardware-specific but does not require host-administrator authority from the evidenced device-side attacker.

4. Primitive and severity reading

This is a real CLASS_B race-induced UAF involving an active pending transaction and its initiator, not merely passive metadata. Competing response and timeout paths can both process one entry after timer cancellation fails. A crash is plausible; useful reclaimed-object consumption, attacker-shaped post-free contents, a directed write, and privilege escalation remain unproven. It therefore does not presently qualify as an Important candidate, and downgrade remains permissible after human confirmation of the unseen processing callbacks.

5. One-sentence report phrase

A malicious FireWire device can race a split response against timeout handling, causing duplicate transaction processing and an initiator-side UAF with plausible kernel crash impact.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm the downstream completion callbacks and whether duplicate processing performs a second release or consumes security-useful stale fields.

7. Call-site confidence

Call-site confidence: medium

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

Patch: firewire: core: fix race condition in split transaction handling [ Upstream
Commit: a8caee0e623ca5d56e829032f9ec073c09e4d224
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a8caee0e623ca5d56e829032f9ec073c09e4d224

Changed files:
  drivers/firewire/core-transaction.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=a8caee0e623ca5d56e829032f9ec073c09e4d224

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

The original Linux kernel CVE announcement for CVE-2026-99185 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99185

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:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: unknown
  Paranoid ActionableScore: 4

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

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).