[CVE-2026-72398][IMPORTANT] sctp: add INIT verification after cookie unpacking [ Upstream

[CVE-2026-72398][IMPORTANT] sctp: add INIT verification after cookie unpacking [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72398
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: sctp: add INIT verification after cookie unpacking [ Upstream
Commit: bca3100f550281c2f2418652338bced3b35af0e6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bca3100f550281c2f2418652338bced3b35af0e6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72398
Analysis date: Sun, 16 Aug 2026 09:12:39 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A remote SCTP peer can tamper with COOKIE-ECHO contents when cookie authentication is disabled, causing the server to process an untrusted reconstructed INIT chunk with possible protocol-state corruption, DoS, and limited out-of-bounds parsing concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72398 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72398

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-2026-72398	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-20;CWE-345;CWE-125;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '8.6';DESCR 'SCTP COOKIE-ECHO processing can reuse an INIT chunk reconstructed from a state cookie without revalidating it when cookie_auth_enable is disabled. A remote peer can obtain a server generated cookie during the normal INIT and INIT-ACK exchange and then return a tampered COOKIE-ECHO, causing the server to process untrusted INIT parameters. For the CVSS the PR:N is used because no local account or prior authentication is required beyond network reachability to the SCTP endpoint. The issue is network reachable on systems exposing SCTP services with cookie authentication disabled. Impact is at least protocol state manipulation and denial of service, and the paranoid score keeps C:L and I:L with A:H because the fix also corrects parameter bounds validation for the embedded INIT length.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	DANGER INIT ERRORPATH UAF NETWORK LINUS KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: **5**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: **+2**. The vulnerable path is SCTP COOKIE-ECHO processing and can be reached by a remote SCTP peer.
* Practical exploit chain demonstrated or strongly implied: **+1**. The sequence is clear: INIT -> INIT-ACK with cookie -> tampered COOKIE-ECHO -> server unpacks and processes untrusted INIT.
* Integrity impact plausible: **+1**. Tampered INIT parameters can affect association setup or protocol state when cookie authentication is disabled.
* Availability impact realistic: **+1**. Invalid reconstructed INIT data can lead to malformed state handling or connection disruption.
* Rare/configuration-dependent exposure: **-1**. Requires an exposed SCTP endpoint and cookie authentication disabled.

Conservative total: **5**

Paranoid additional signals:

* Memory corruption, weak/indirect corruption candidate: **+1**. The bounds fix changes validation from `chunk->chunk_end` to the actual embedded INIT length, suggesting possible parameter parsing beyond the trusted embedded INIT boundary.
* Confidentiality impact plausible: **+1**. Limited out-of-bounds parameter interpretation may expose or reflect unintended cookie-buffer contents in error handling, but no arbitrary read primitive is proven.
* Common networking protocol receive path: **+1**. This is a kernel network protocol parser reachable through packet processing, even if SCTP deployment is less common than TCP/UDP.

Paranoid total: **7**

## 3. Reachability analysis

A remote peer can trigger this if it can reach an SCTP service and complete the initial INIT/INIT-ACK exchange. No local account is required, so this is **PR:N** in CVSS terms. The bug depends on `cookie_auth_enable` being disabled, which reduces exposure, but the affected path is still a network-facing kernel protocol parser. Namespaces do not materially reduce the remote attack requirement, though containerized SCTP services could expose the host kernel path depending on network namespace and protocol availability.

Call-site confidence: **high**, because both COOKIE-ECHO processing call sites and the cookie unpacking / INIT validation logic are present in the supplied patch.

## 4. Severity interpretation

This is more than an ordinary Moderate because it is remotely reachable and affects kernel SCTP handshake validation. Conservatively, it is an **Actionable Moderate** due to remote protocol-state manipulation and realistic availability impact. Paranoid handling as a **Strong Important candidate** is defensible because the patch also fixes parameter-bound validation for an embedded INIT object, creating a weak but relevant concern for out-of-bounds parsing in a network protocol path. There is no supported evidence of arbitrary write, UAF, or reliable privilege escalation.

## 5. One-sentence report phrase

A remote SCTP peer can tamper with COOKIE-ECHO contents when cookie authentication is disabled, causing the server to process an untrusted reconstructed INIT chunk with possible protocol-state corruption, DoS, and limited out-of-bounds parsing concern.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is a network-reachable kernel protocol parser issue with an explicit validation bypass and a bounds-check correction. Even though strong memory corruption is not proven, the remote reachability and embedded INIT length bug make auto-close unsafe.

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

Patch: sctp: add INIT verification after cookie unpacking [ Upstream
Commit: bca3100f550281c2f2418652338bced3b35af0e6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bca3100f550281c2f2418652338bced3b35af0e6

Changed files:
  net/sctp/sm_make_chunk.c
  net/sctp/sm_statefuns.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=bca3100f550281c2f2418652338bced3b35af0e6

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

The original Linux kernel CVE announcement for CVE-2026-72398 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72398

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:L/PR:N/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 8.6

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: 7

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).