[CVE-2026-64543][MODERATE 7.0] tipc: fix use-after-free of the discoverer in tipc_disc_rcv() [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-64543
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: tipc: fix use-after-free of the discoverer in tipc_disc_rcv() [ Upstream
Commit: 5e215bf1c47fdddf8203a0fe80a0ed594065f101
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5e215bf1c47fdddf8203a0fe80a0ed594065f101
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64543
Analysis date: Wed, 29 Jul 2026 02:03:55 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate at minimum, manual review should not be skipped.
Manual review required: YES

Summary:
A TIPC UDP bearer lifetime race can free the discoverer with plain kfree while tipc_disc_rcv still reads it under rcu_read_lock, allowing an unprivileged local namespace user to trigger a kernel use-after-free and likely crash the system.

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

The original Linux kernel CVE announcement for CVE-2026-64543 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64543

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-64543	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:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use-after-free can occur in the TIPC UDP bearer receive path because bearer_disable can free b disc while tipc_disc_rcv still dereferences it from RX softirq under rcu_read_lock. The L2 bearer path had a synchronize_net grace period, but the UDP bearer defers that synchronization to cleanup work, leaving a window where an in flight packet can reach freed discoverer memory. For the CVSS the PR:L is selected because the TIPCv2 generic netlink family is netnsok and the bearer commands are described as lacking GENL_ADMIN_PERM, so an unprivileged local user namespace can reach the vulnerable control path when CONFIG_TIPC and CONFIG_TIPC_MEDIA_UDP are enabled. The issue is not a pure remote Internet vector because reliable triggering needs local namespace or bearer control, but packet reception over UDP is part of the race window. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to kernel heap use-after-free, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) 	MAYBE	READ OOB DANGER INIT TIPC UAF SKB TIMER LINUS  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate at minimum, manual review should not be skipped.

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  The commit states that this is reachable from an unprivileged user namespace because the TIPCv2 generic netlink family is netnsok and bearer commands lack GENL_ADMIN_PERM.

* Memory corruption, weak primitive: +1
  This is a real KASAN-confirmed slab use-after-free in tipc_disc_rcv. However, the demonstrated access is a stale read in a race window, with no shown attacker-controlled reclaim, write-after-free, type confusion, callback control, or arbitrary write.

* Real lifetime corruption: +1
  The bug is an RCU lifetime issue. b->disc is freed with plain kfree while RX softirq readers can still dereference it under rcu_read_lock.

* Reliable kernel crash / strong DoS: +1
  The KASAN trace shows a slab-use-after-free reachable through the TIPC UDP receive path and bearer disable path, which is a credible kernel crash / DoS condition.

Paranoid-only signal:

* Packet-processing path exposure: +1
  The stale pointer is dereferenced from the UDP receive path through tipc_udp_recv -> tipc_rcv -> tipc_disc_rcv. This is not a pure remote Internet vector, but packet reception participates in the race and increases triage relevance.

Potential negative signal:

* Hard or unreliable race: -1 in conservative interpretation
  The bug is race-dependent. Conservative scoring applies the race penalty because the exploitability beyond crash depends on timing between bearer disable and RX softirq processing. Paranoid scoring does not subtract it because the report includes a PoC-like KASAN trace and the local attacker can likely coordinate bearer operations and UDP traffic.

Not awarded:

* Strong LPE plausibility: +0
  No attacker-controlled reclaim, object replacement, write primitive, callback dispatch, refcount takeover, or type confusion is shown.

* Confidentiality / Integrity impact: +0 conservative
  The demonstrated primitive is stale read and crash. C/I impact remains theoretical.

## 3. Reachability analysis

A local unprivileged user can plausibly trigger the vulnerable control path from an unprivileged user namespace if CONFIG_TIPC and CONFIG_TIPC_MEDIA_UDP are enabled. The relevant TIPC generic netlink bearer commands are described as netnsok and not protected by GENL_ADMIN_PERM, so this should not be treated as requiring full host root or CAP_NET_ADMIN in the initial namespace.

The receive-side dereference occurs in softirq context through UDP packet processing. This does not make the issue generally remote reachable by itself, because reliable triggering requires local namespace or bearer-control activity to free the discoverer at the right time. Remote packets may contribute to the race window after local setup, but the main attacker model is local unprivileged.

Default exposure depends on product configuration. TIPC and UDP media support are not universal on all kernels, but when available they are reachable through ordinary namespace and netlink mechanisms rather than requiring rare hardware.

Call-site confidence: high. The commit message includes both the freeing path and the RX dereference path.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is a real kernel UAF in a network receive path and is stated to be reachable from an unprivileged user namespace. The realistic demonstrated impact is local DoS via kernel crash.

It is not automatically a strong Important by conservative evidence because the patch does not show a controlled reclaim, write-after-free, object replacement, type confusion, or arbitrary write primitive. The paranoid score treats it as Actionable Moderate at minimum because kernel heap UAF bugs in network paths have historically been underestimated and should receive manual review.

## 5. One-sentence report phrase

A TIPC UDP bearer lifetime race can free the discoverer with plain kfree while tipc_disc_rcv still reads it under rcu_read_lock, allowing an unprivileged local namespace user to trigger a kernel use-after-free and likely crash the system.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a confirmed UAF with unprivileged namespace reachability and packet receive involvement. Even though the demonstrated primitive is mainly DoS, the lifetime bug class and network RX context make it unsafe to auto-close.

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

Patch: tipc: fix use-after-free of the discoverer in tipc_disc_rcv() [ Upstream
Commit: 5e215bf1c47fdddf8203a0fe80a0ed594065f101
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5e215bf1c47fdddf8203a0fe80a0ed594065f101

Changed files:
  net/tipc/discover.c
  net/tipc/node.c
  net/tipc/udp_media.c
  net/ipv4/udp.c
  net/ipv4/ip_input.c
  mm/slub.c
  net/tipc/bearer.c
  net/tipc/core.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=5e215bf1c47fdddf8203a0fe80a0ed594065f101

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

The original Linux kernel CVE announcement for CVE-2026-64543 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64543

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:L/I:L/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: 4
  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: 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).