[CVE-2026-74255][MODERATE 7.0] tipc: fix UAF in tipc_l2_send_msg() [ Upstream

[CVE-2026-74255][MODERATE 7.0] tipc: fix UAF in tipc_l2_send_msg() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74255
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: tipc: fix UAF in tipc_l2_send_msg() [ Upstream
Commit: 609ced2301be1df7e7ed2ef47d1d916674e6ba3b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=609ced2301be1df7e7ed2ef47d1d916674e6ba3b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74255
Analysis date: Sun, 16 Aug 2026 03:10:40 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-74255 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74255

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-2026-74255	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in the TIPC L2 bearer disable path can leave b.media_ptr visible to RCU readers while the underlying net_device is being detached and released. A concurrent reader in tipc_l2_send_msg can then use a stale device pointer and reach a slab use after free in ipvlan_hard_header, causing at least a kernel crash. For the CVSS the PR:L is used for the paranoid score because reduced capability root, container root, or delegated CAP_NET_ADMIN may be enough to control TIPC bearer state in some deployments. The issue is not proven to be directly network reachable by packet traffic alone, but network activity can participate in the race once bearer teardown is triggered. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to a race based UAF in kernel networking code.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)	YES	DANGER INIT TIPC UAF HARDWARE LINUS SYZBOT PACKET  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

1. ActionableScore
* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

2. Signal breakdown
* Race-dependent UAF / weak memory corruption candidate: +1. The patch fixes a real slab-use-after-free, but no attacker-controlled reclaim, overwrite, callback control, or type confusion is shown.
* Real lifetime corruption: +1. The bug is an RCU lifetime issue where b->media_ptr can remain visible while the referenced net_device is later released.
* Reliable kernel crash / strong DoS: +1. Syzbot observed slab-use-after-free in ipvlan_hard_header() from tipc_l2_send_msg().
* Availability impact realistic: +1 in the paranoid score. A successful trigger can crash the kernel or cause serious host instability.
* Networking packet path involvement: +1 in the paranoid score. The stale pointer is consumed from TIPC L2 send path and reaches a network device header operation, though this is not proven to be remotely triggerable by packets alone.
* Hard race / special timing: -1. The issue depends on concurrent bearer teardown and RCU readers.
* Requires CAP_NET_ADMIN or equivalent in typical deployments: -2 for the conservative score. For the paranoid score this penalty is reduced because delegated CAP_NET_ADMIN, container root, or reduced-capability service contexts may make the trigger less than full host-root.

3. Reachability analysis
The reliable trigger appears local and control-plane oriented: an attacker needs to influence TIPC L2 bearer teardown or network configuration while another path sends through the bearer. In typical host deployments this requires CAP_NET_ADMIN or root-level network administration rights. Namespaces and containers matter because CAP_NET_ADMIN can be delegated to less trusted container or service contexts, so PR:L is defensible for paranoid triage. The issue is not demonstrated as directly remote packet-triggerable, but network activity can participate in the race once local bearer teardown is initiated. TIPC is not a universal default exposure, but it is a kernel networking subsystem and UAF in this area deserves manual review.

4. Severity interpretation
This is stronger than an ordinary Moderate because it is a confirmed UAF, not merely a warning or resource leak. Realistically, the demonstrated impact is kernel crash / DoS under a race window with privileged or delegated network-control access. Theoretical privilege escalation is not proven because the patch does not show controlled reclaim, write-after-free, type confusion, callback dispatch, or refcount takeover. Paranoid handling as Actionable Moderate is justified to avoid auto-closing a network-subsystem RCU lifetime UAF.

5. One-sentence report phrase
A race in TIPC L2 bearer teardown can leave b.media_ptr visible to RCU readers after the underlying net_device is released, causing a slab-use-after-free in tipc_l2_send_msg() and at least a local kernel crash, with higher concern in delegated CAP_NET_ADMIN or containerized environments.

6. Manual review recommendation
MANUAL CHECK REQUIRED. This is a confirmed race-based UAF in a networking subsystem, and although practical LPE is not demonstrated, the lifetime bug class and delegated capability scenarios make auto-close unsafe.

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

Patch: tipc: fix UAF in tipc_l2_send_msg() [ Upstream
Commit: 609ced2301be1df7e7ed2ef47d1d916674e6ba3b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=609ced2301be1df7e7ed2ef47d1d916674e6ba3b

Changed files:
  net/tipc/bearer.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=609ced2301be1df7e7ed2ef47d1d916674e6ba3b

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

The original Linux kernel CVE announcement for CVE-2026-74255 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74255

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:H/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:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 5

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 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).