[CVE-2026-64564][IMPORTANT] sctp: don't free the ASCONF's own transport in DEL-IP processing

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

CVE: CVE-2026-64564
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: sctp: don't free the ASCONF's own transport in DEL-IP processing
Commit: fedeb4468987bcaff85fe3061de5ae052d414740
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fedeb4468987bcaff85fe3061de5ae052d414740
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64564
Analysis date: Tue, 04 Aug 2026 03:02:42 -0400
ActionableScore: 8
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A remote SCTP peer can trigger a use-after-free in ASCONF DEL-IP handling by freeing the cached ASCONF transport and then reusing it through wildcard DEL-IP processing, causing at least remote kernel DoS and requiring manual review for possible broader UAF impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64564 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64564

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-2026-64564	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-825;*CWE-664;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'A use after free can occur in SCTP ASCONF DEL-IP processing because `asconf transport` may point to the transport selected by the ASCONF Address Parameter rather than the packet source address. A remote SCTP peer can craft one ASCONF with an Address Parameter for L, a DEL-IP for L, and then a wildcard DEL-IP for 0.0.0.0, causing the cached transport to be freed and then reused by later wildcard handling. The freed transport may be dereferenced and may also be stored as the association primary_path or active_path, leaving association state with dangling transport pointers. For the CVSS the PR:N is used because no local account or local code execution on the victim is required, only network reachability and ability to act as an SCTP peer that can send ASCONF. AC:H is used because reliable triggering depends on SCTP association state, ADD-IP ASCONF processing, and a specific parameter order. Impact is at least remote denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact due to a kernel use after free, so this should be manually reviewed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	OOB DANGER UAF NETWORK LINUS KPANIC PACKET 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  SCTP ASCONF processing is reachable from a remote SCTP peer when SCTP and ADD-IP ASCONF handling are in use.

* Memory corruption, strong corruption primitive: +2
  The commit explicitly describes a use-after-free: `sctp_assoc_rm_peer()` frees the transport, and later wildcard DEL-IP handling reuses the dangling `asconf->transport`.

* Real lifetime corruption: +1
  This is a stale pointer after free with RCU-deferred lifetime semantics.

* Reliable kernel crash / strong DoS: +1
  The freed transport is dereferenced via `->ipaddr` and `->state`, and dangling pointers can be stored into `primary_path` / `active_path`.

* Hard or state-dependent triggering: -1
  Triggering requires a valid SCTP association, ASCONF / ADD-IP behavior, and a specific ordering of ASCONF parameters.

Conservative subtotal: 5

Paranoid additional signals:

* Weak-to-moderate LPE concern: +1
  The bug leaves freed transport pointers in persistent SCTP association state. No controlled reclaim or write primitive is shown, but persistent dangling kernel pointers justify manual-review sensitivity.

* Confidentiality impact plausible: +1
  Not proven, but UAF reuse in network object state may theoretically expose stale object contents or influence later reads.

* Integrity impact plausible: +1
  Not proven, but storing a freed object pointer as `primary_path` / `active_path` creates corrupted association state that may affect later kernel decisions.

Paranoid subtotal: 8

## 3. Reachability analysis

A remote SCTP peer can potentially trigger the bug by sending a crafted ASCONF sequence after an SCTP association is established. No local account on the victim is required, so the practical PR interpretation is PR:N. The path is not as broadly exposed as TCP or UDP because SCTP and ASCONF ADD-IP must be enabled and reachable, but it is still a real network protocol path rather than a local ioctl or admin-only control plane. Containers and namespaces do not materially reduce the remote attack requirement on the victim side, although deployment exposure depends heavily on whether SCTP traffic is allowed by firewall and whether the service uses SCTP multihoming or ADD-IP.

Call-site confidence: high. The commit message directly identifies the freeing call, the later reuse sites, and the persistent dangling fields.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is a network-reachable kernel UAF with persistent dangling transport pointers. Realistic demonstrated impact is at least remote DoS through dereference of freed transport state. Practical privilege escalation or code execution is not demonstrated, because there is no shown attacker-controlled reclaim, overwrite, callback dispatch, or type confusion primitive. However, the combination of remote reachability, UAF, and corrupted association state makes it an Important candidate for manual review rather than something that should be auto-closed as a simple crash.

## 5. One-sentence report phrase

A remote SCTP peer can trigger a use-after-free in ASCONF DEL-IP handling by freeing the cached ASCONF transport and then reusing it through wildcard DEL-IP processing, causing at least remote kernel DoS and requiring manual review for possible broader UAF impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a network-reachable kernel use-after-free with dangling pointers stored in SCTP association state. Even though the proven impact is DoS, the primitive is strong enough to require manual security review.

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

Patch: sctp: don't free the ASCONF's own transport in DEL-IP processing
Commit: fedeb4468987bcaff85fe3061de5ae052d414740
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fedeb4468987bcaff85fe3061de5ae052d414740

Commit description:

sctp_process_asconf() caches the transport the ASCONF chunk is processed
against in asconf->transport (== chunk->transport, set once in sctp_rcv()).
For an ASCONF located through its Address Parameter by
__sctp_rcv_asconf_lookup(), that cached transport corresponds to the
Address Parameter, which need not be the packet's source address.

sctp_process_asconf_param() rejects a DEL-IP for the packet source address
(ADDIP D8, SCTP_ERROR_DEL_SRC_IP), but nothing protects asconf->transport.
A single ASCONF can therefore carry, in order:

    [Address Parameter L] [DEL-IP L] [DEL-IP 0.0.0.0]

where L differs from the source. The DEL-IP for L passes the D8 check and
calls sctp_assoc_rm_peer() on the transport that asconf->transport still
points at, freeing it (RCU-deferred). The following wildcard DEL-IP then
reuses the now-dangling asconf->transport in sctp_assoc_set_primary() and
sctp_assoc_del_nonprimary_peers(): set_primary() dereferences the freed
transport (->ipaddr, ->state) and plants the dangling pointer into
asoc->peer.primary_path / active_path, and del_nonprimary_peers(), keeping
only the pointer that is no longer on the list, removes every real
transport, leaving the association with a transport_count of 0 and
primary_path/active_path pointing at freed memory.

Reject a DEL-IP that targets the transport the ASCONF is being processed
against, mirroring the existing source-address guard, so the wildcard
branch can never reuse a freed transport.

Fixes: 42e30bf ("[SCTP]: Handle the wildcard ADD-IP Address parameter")
Cc: stable@kernel.org
Signed-off-by: Jun Yang <junvyyang@tencent.com>
Acked-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/tencent_73762ED1DF08CC9D5F5F61954B01350CFE0A@qq.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/sctp/sm_make_chunk.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=fedeb4468987bcaff85fe3061de5ae052d414740

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

The original Linux kernel CVE announcement for CVE-2026-64564 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64564

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:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 5
  Paranoid ActionableScore: 8

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: YES
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).