[CVE-2026-68376][IMPORTANT] sctp: fix auth_hmacs array size in struct sctp_cookie [ Upstream

[CVE-2026-68376][IMPORTANT] sctp: fix auth_hmacs array size in struct sctp_cookie [ Upstream

[AL-KERNEL]

CVE: CVE-2026-68376
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: sctp: fix auth_hmacs array size in struct sctp_cookie [ Upstream
Commit: 0b4414e43e0861d67276031cc21401d7e87de3da
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b4414e43e0861d67276031cc21401d7e87de3da
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68376
Analysis date: Mon, 10 Aug 2026 09:34:27 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A network-reachable SCTP-AUTH cookie layout bug can cause a two-byte overflow from `auth_hmacs` into adjacent authentication state, potentially allowing invalid HMAC handling and a later out-of-bounds read in `sctp_auth_get_hmac()`.

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

The original Linux kernel CVE announcement for CVE-2026-68376 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68376

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
======================================================================

CVE-2026-68376	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-131;*CWE-787;CWE-125;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 fixed-size buffer in struct sctp_cookie for SCTP/AUTH HMAC-ALGO data was two bytes too small because it did not reserve the full SCTP parameter header size. When four HMAC identifiers are configured, association setup can copy past auth_hmacs and corrupt the adjacent auth_chunks field. This is a network protocol memory-corruption case that can later allow an invalid HMAC identifier and an out-of-bounds read in sctp_auth_get_hmac. For the CVSS the PR:N is used because a remote SCTP peer can trigger the vulnerable association path without local privileges when the SCTP endpoint is reachable and already configured with the affected HMAC list. AC:H is used because exploitation depends on SCTP/AUTH being enabled and on a specific non-default HMAC configuration. Impact is at least denial of service and may include confidentiality or integrity impact due to kernel memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-68376 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	REMOTE OOB SIMPLEFIX NETWORK KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	-	-	checked

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

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**
  SCTP association setup is a network protocol path. A remote SCTP peer can plausibly reach the affected logic if SCTP and SCTP-AUTH are enabled and the endpoint is configured with the affected HMAC list.

* **Constrained kernel buffer overwrite: +1**
  `auth_hmacs` is undersized by 2 bytes, and `sctp_association_init()` can copy past the end of the field into adjacent `auth_chunks`. This is an OOB write, but the overwrite appears narrow and layout-specific.

* **Memory layout invariant restoration: +1**
  The patch restores the correct relationship between SCTP parameter header size and the fixed cookie layout.

* **Reliable kernel crash / strong DoS: +1**
  The commit explicitly states that the corruption can later cause an out-of-bounds read in `sctp_auth_get_hmac()`, which is a credible kernel crash path.

* **Integrity impact plausible: +1**
  Corruption of `auth_chunks` may alter SCTP-AUTH state and allow an invalid HMAC identifier to be accepted.

Negative signals:

* **Hard or configuration-dependent trigger: -1**
  The issue requires SCTP-AUTH and a specific configuration with four HMAC identifiers.

Paranoid additional interpretation:

* **Generic memory corruption: +2 instead of constrained overwrite +1**
  Because the bug is a network-reachable OOB write into an adjacent protocol-state field, the paranoid score treats it as a stronger memory-corruption candidate.

* **Confidentiality impact plausible: +1**
  The later OOB read in `sctp_auth_get_hmac()` may expose or consume unintended kernel memory, although no direct disclosure primitive is demonstrated.

* **Weak LPE concern: +1**
  The corruption is real and occurs in kernel networking state, but there is no demonstrated reclaim, arbitrary write, callback control, or type confusion. This is only a manual-review concern, not a proven LPE path.

## 3. Reachability analysis

A remote SCTP peer can likely trigger the association initialization path when the target exposes SCTP and SCTP-AUTH. No local privileges on the victim are required in that network-facing scenario, so PR:N is reasonable for CVSS-style triage.

The main practical limitation is configuration. The vulnerable condition requires four configured HMAC identifiers, which is not necessarily a default deployment. SCTP itself is less commonly exposed than TCP or UDP services, but it is still a real network protocol attack surface where enabled.

Namespaces and containers do not materially reduce concern for the network-facing case. If SCTP is only used locally or blocked by firewall policy, exposure is reduced, but the primitive remains security-relevant.

Call-site confidence: **high**. The commit directly names both the overflowing copy in `sctp_association_init()` and the later OOB read in `sctp_auth_get_hmac()`.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because the patch fixes a concrete OOB write in a network protocol structure and the commit describes a downstream OOB read. Conservative handling fits **Actionable Moderate** due to the constrained overwrite and configuration dependency.

The paranoid interpretation reaches **Strong Important candidate** because the bug is network-triggerable memory corruption in kernel SCTP-AUTH state. However, practical privilege escalation is not demonstrated. The strongest supported impact is remote DoS plus possible confidentiality or integrity impact from memory corruption and OOB read behavior.

## 5. One-sentence report phrase

A network-reachable SCTP-AUTH cookie layout bug can cause a two-byte overflow from `auth_hmacs` into adjacent authentication state, potentially allowing invalid HMAC handling and a later out-of-bounds read in `sctp_auth_get_hmac()`.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is network-reachable kernel memory corruption with an OOB write into adjacent protocol state and a described OOB read follow-up. The trigger is configuration-dependent, but it should not be auto-closed.

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

Patch: sctp: fix auth_hmacs array size in struct sctp_cookie [ Upstream
Commit: 0b4414e43e0861d67276031cc21401d7e87de3da
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b4414e43e0861d67276031cc21401d7e87de3da

Changed files:
  include/net/sctp/structs.h

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=0b4414e43e0861d67276031cc21401d7e87de3da

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

The original Linux kernel CVE announcement for CVE-2026-68376 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68376

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: 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).