[CVE-2026-74490][MODERATE REGULAR] tipc: avoid use-after-free in poll trace queue dumps

[CVE-2026-74490][MODERATE REGULAR] tipc: avoid use-after-free in poll trace queue dumps

[AL-KERNEL]

CVE: CVE-2026-74490
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: tipc: avoid use-after-free in poll trace queue dumps
Commit: d7940bb6a8e7ab28f972c2875cb05783216312dc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d7940bb6a8e7ab28f972c2875cb05783216312dc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74490
Analysis date: Sat, 15 Aug 2026 09:32:08 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / Actionable Moderate candidate
Manual review required: YES

Summary:
TIPC poll tracing can dereference a stale skb queue entry because tipc_poll() requested an unlocked queue dump, allowing a local race with skb dequeue/free and causing a potential kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-74490 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74490

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-2026-74490	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'TIPC poll tracing can hit a use-after-free because tipc_poll() requested TIPC_DUMP_ALL without holding the socket locks used by other queue dump sites. When the tracepoint is active, the trace helper can walk queue entries while another context dequeues and frees an skb, leaving a stale entry to be dereferenced during the dump. For the CVSS the PR:L is used because a local user or local process able to exercise TIPC sockets and poll() can trigger the vulnerable path when tracing is enabled. The issue is not directly network reachable because packet traffic alone does not call the local poll trace path, although remote TIPC traffic may help create queue activity in configured TIPC deployments. Impact is at least local denial of service via kernel crash, and in the paranoid case may include limited confidentiality or integrity impact from UAF based stale memory access, so this should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate candidate (with actual score 4)	YES	LOCK TIPC UAF LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / Actionable Moderate candidate**

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local process that can use TIPC sockets and call poll() can reach tipc_poll() if TIPC is configured.

* Memory corruption, weak/indirect corruption candidate: +1
  The patch and commit describe a stale skb queue entry dereference, i.e. a race-dependent UAF read/deref in trace dumping. No reclaim, overwrite, callback control, or type confusion is shown.

* Real lifetime corruption: +1
  The bug is explicitly a lifetime race where another context can dequeue and free an skb while the trace helper walks the queue.

* Reliable kernel crash / strong DoS: +1
  Dereferencing a freed skb from a trace helper can plausibly cause Oops/panic or KASAN UAF.

Subtracted signals:

* Hard or unreliable race / special timing required: -1
  The issue depends on a concurrent poll trace queue dump and skb dequeue/free window.

Paranoid-only consideration:

* The stale skb dereference is UAF in networking code, so manual review is justified, but the patch does not show attacker-controlled reclaim, write-after-free, callback dispatch, or refcount takeover. Therefore the score is not raised into Important range.

## 3. Reachability analysis

The vulnerable path is local control-plane/socket activity through tipc_poll(), not direct packet processing. Remote TIPC traffic may help create queue churn, but packet traffic alone does not invoke the local poll trace path.

The issue likely requires TIPC to be configured and the relevant tracepoint path to be active. Enabling tracing is typically privileged, but once tracing is enabled, a local user or process able to exercise TIPC sockets may trigger the vulnerable poll path. Namespace/container impact depends on whether TIPC sockets and tracing are exposed or delegated, which is not guaranteed in typical deployments.

Call-site confidence: high, because the changed call site is directly shown and the commit explains the unlocked queue dump path.

## 4. Severity interpretation

This behaves more like a borderline/actionable Moderate than a Strong Important issue. Theoretical memory corruption exists because this is a race-dependent UAF, but realistic exploitation evidence points mainly to crash/DoS. The patch does not support privilege escalation, attacker-controlled reuse, arbitrary write, or object replacement.

Manual triage should not auto-close it because it is a UAF in networking-related code, but the demonstrated primitive is weak and trace-dependent.

## 5. One-sentence report phrase

TIPC poll tracing can dereference a stale skb queue entry because tipc_poll() requested an unlocked queue dump, allowing a local race with skb dequeue/free and causing a potential kernel crash.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: race-dependent UAF in a networking subsystem should be reviewed, but current evidence supports mainly DoS and does not justify Important classification without additional reclaim or write primitive evidence.

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

Patch: tipc: avoid use-after-free in poll trace queue dumps
Commit: d7940bb6a8e7ab28f972c2875cb05783216312dc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d7940bb6a8e7ab28f972c2875cb05783216312dc

Commit description:

TIPC socket tracepoints dump queue state through tipc_sk_dump(). Most
queue-dump callsites already serialize that walk under the socket lock or
sk->sk_lock.slock, but tipc_poll() calls trace_tipc_sk_poll(...,
TIPC_DUMP_ALL, ...) without holding either lock.

That lets the poll trace path reach tipc_list_dump() and backlog head/tail
dumping while another context dequeues and frees an skb, leaving the trace
helper dereferencing a stale queue entry.

Stop the unlocked poll trace site from requesting queue dumps. Other queue
dump trace callsites keep their existing output under the locking they
already provide, while poll still emits the event itself without walking
live queue members from an unlocked context.

Fixes: b4b9771 ("tipc: enable tracepoints in tipc")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Signed-off-by: Zihan Xi <zihanx@nebusec.ai>
Signed-off-by: Ren Wei <enjou1224z@gmail.com>
Reviewed-by: Tung Nguyen <tung.quang.nguyen@est.tech>
Link: https://patch.msgid.link/f8119abd5e5ecc400597de667ae9d39656de56d0.1784794294.git.zihanx@nebusec.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/tipc/socket.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=d7940bb6a8e7ab28f972c2875cb05783216312dc

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

The original Linux kernel CVE announcement for CVE-2026-74490 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74490

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:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 3
  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: 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).