[CVE-2026-99246][MODERATE 7.0] tipc: protect node reset trace dump with node lock

[CVE-2026-99246][MODERATE 7.0] tipc: protect node reset trace dump with node lock

[AL-KERNEL]

CVE: CVE-2026-99246
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: tipc: protect node reset trace dump with node lock
Commit: c8b72ca0918e95f708f67c8b3e69b05290f2b6d2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c8b72ca0918e95f708f67c8b3e69b05290f2b6d2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99246
Analysis date: Tue, 03 Nov 2026 22:33:30 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A trace-versus-bearer-teardown race permits `tipc_link_dump()` to read a freed TIPC link, causing a confirmed slab UAF and plausible kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-99246 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99246

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 7.0
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-2026-99246	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99246 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=6 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both 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:L/I:N/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.9';DESCR 'A race in tipc_node_reset_links allows tipc_node_dump to retain a link pointer while concurrent bearer teardown frees that link under the node write lock. The later tipc_link_dump call dereferences the stale pointer and KASAN confirms a slab use after free read. AV:A reflects that practical packet reachability normally requires access to a configured TIPC bearer or cluster network. AC:H reflects the need for the trace event to be active and for link deletion to overlap the trace dump. For the CVSS the PR:N value is used because a peer able to send accepted TIPC traffic does not need an authenticated kernel user context, although reliable reproduction also depends on concurrent bearer teardown. The demonstrated impact is a kernel crash or instability. The paranoid confidentiality impact is low because reused slab data might enter the trace dump, but no write primitive or supported privilege escalation path is shown. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 5.9 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 CVSS and initial triage stage IMPORTANT to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS. The independent weaker Aegis shadow evaluated CVSS 3.1 and ActionableScore 6 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	READ TIPC LEAK UAF HARDWARE LINUS  KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS 	-	-	checked

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

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

1. ActionableScore

* Raw base score: 1.
* Conservative score: 4. Real-UAF floor 4 applied: 1 -> 4.
* Raw paranoid score: 1.
* Paranoid score: 4. Real-UAF floor 4 applied: 1 -> 4.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 — Confirmed slab UAF: bearer teardown frees `n->links[0].link`, after which `tipc_link_dump(l)` reads the stale object; KASAN confirms the read.
* +1 — Plausible kernel crash/instability from the stale structured-object dereference.
* -1 — Materially difficult race: tracing must be enabled and overlap link deletion.
* -1 — Unusual, attacker-noninstantiable setup: an active TIPC bearer plus enabled trace event and concurrent bearer teardown are required.
* Floor 4 — The stale reference is genuinely consumed and is not merely a fixed async buffer.

Not awarded: controlled reclaim, post-free write, callback control, repeated refcount mutation, authorization bypass, or attacker-readable disclosure. Trace-buffer exposure of reused bytes is not enough to establish confidentiality impact. No extra Availability point duplicates the same crash. NEW52/B5-R does not apply because no retry-accumulated OOB write exists.

3. Reachability analysis

Accepted TIPC traffic reaches `tipc_node_reset_links()` through `tipc_udp_recv()` and `tipc_rcv()`, but the complete race also requires locally enabled tracing and concurrent bearer teardown. The evidence does not show that a remote peer can initiate teardown or configure tracing. Conversely, host-admin control is not proven necessary for the packet-side operation, so the complete-trigger privilege remains unknown. Namespace-scoped capability sufficiency is also unestablished. The race is explicitly timing-sensitive rather than cheaply attacker-controlled.

4. Primitive and severity reading

This is a CLASS_B active-structured-object UAF read: a freed `tipc_link` is passed into the trace dump and its fields are dereferenced. It is not a fixed stale buffer, but the shown use is observational tracing rather than broader active link processing. The supported consequence is crash/instability; disclosure, write corruption, LPE, and a useful post-reclaim primitive remain unproven.

ImportantCandidate is NO because neither material reuse control nor a specific boundary-crossing primitive is shown. AutoDowngradeAllowed is YES because the demonstrated path is a constrained, high-complexity stale read without unresolved write-like leverage.

5. One-sentence report phrase

A trace-versus-bearer-teardown race permits `tipc_link_dump()` to read a freed TIPC link, causing a confirmed slab UAF and plausible kernel crash.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm product TIPC exposure, trace-event activation, and whether any peer-accessible mechanism can induce link deletion or observe trace output.

7. Call-site confidence

Call-site confidence: high

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

Patch: tipc: protect node reset trace dump with node lock
Commit: c8b72ca0918e95f708f67c8b3e69b05290f2b6d2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c8b72ca0918e95f708f67c8b3e69b05290f2b6d2

Commit description:

The tipc_node_reset_links trace event asks tipc_node_dump() to walk the
node's link entries. Unlike the other node events that request link data,
this event runs without the node lock.

This permits bearer teardown to free a link while the trace callback is
dumping it:

  CPU 0                                CPU 1
  trace_tipc_node_reset_links()
    tipc_node_dump()
      l = n->links[0].link
                                       tipc_node_write_lock()
                                       kfree(l)
                                       n->links[0].link = NULL
                                       tipc_node_write_unlock()
      tipc_link_dump(l)

tipc_link_dump() then dereferences the stale pointer. KASAN reported:

  BUG: KASAN: slab-use-after-free in tipc_link_dump
  Read of size 4 by task poc/115
  Call Trace:
   tipc_link_dump+0x10cb/0x16b0
   tipc_node_dump+0x4bb/0x740
   trace_event_raw_event_tipc_node_class+0x258/0x360
   tipc_node_reset_links+0x14d/0x1a0
   tipc_rcv+0x13f5/0x3030
   tipc_udp_recv+0x4e3/0x670
  Allocated by task 0:
   tipc_link_create+0x1e1/0x1020
   tipc_node_check_dest+0x7d2/0x11a0
   tipc_disc_rcv+0xdbf/0x1430
  Freed by task 89:
   kfree+0x131/0x3c0
   tipc_node_link_down+0x267/0x4b0
   tipc_node_delete_links+0xec/0x160
   bearer_disable+0x107/0x260

Take the node write lock around the trace event. This serializes the
dump against tipc_node_link_down(delete=true), which frees the link
under the same write lock.

Fixes: eb18a51 ("tipc: add trace_events for tipc node")
Cc: stable@vger.kernel.org
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
Reviewed-by: Tung Nguyen <tung.quang.nguyen@est.tech>
Link: https://patch.msgid.link/20260825190141.242219-1-nicoyip.dev@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/tipc/node.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=c8b72ca0918e95f708f67c8b3e69b05290f2b6d2

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

The original Linux kernel CVE announcement for CVE-2026-99246 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99246

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 5.9

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: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).