[CVE-2026-64047][MODERATE 7.0] net: tls: fix off-by-one in sg_chain entry count for wrapped sk_msg ring [ Upstream

[CVE-2026-64047][MODERATE 7.0] net: tls: fix off-by-one in sg_chain entry count for wrapped sk_msg ring [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64047
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net: tls: fix off-by-one in sg_chain entry count for wrapped sk_msg ring [ Upstream
Commit: 73963a375885d5ccb7def39fd0b4f542e0f343dd
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=73963a375885d5ccb7def39fd0b4f542e0f343dd
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64047
Analysis date: Sun, 19 Jul 2026 12:04:20 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A local kTLS sender may trigger an off-by-one scatterlist chaining bug when an sk_msg ring wraps, corrupting TLS transmit scatterlist metadata and potentially causing a kernel crash or other unintended crypto API memory access.

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

The original Linux kernel CVE announcement for CVE-2026-64047 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64047

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
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CVE-2026-64047	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-193;CWE-119;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A scatterlist off-by-one in the TLS transmit path can occur when an sk_msg ring wraps and tls_push_record chains the tail of the ring back to the head. The old sg_chain entry count can place the chain marker at data MAX_SKB_FRAGS instead of the reserved final scatterlist entry, which may corrupt the scatterlist layout later consumed by the crypto API. For the CVSS the PR:L is used because a local process that can create and write to a kTLS socket is the most realistic trigger, while a remote peer normally cannot directly control the local TX scatterlist ring. The issue is not directly network reachable as packet input, although it affects networking code and could be exposed by local services using kTLS. Impact is at least local denial of service and in the paranoid interpretation may include confidentiality or integrity impact if malformed scatterlist traversal reaches unintended memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 6)	YES	REMOTE SKB KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local process can realistically exercise the kTLS transmit path by creating and writing to a TLS socket, assuming kTLS is enabled and available in the product configuration.

* Constrained kernel buffer or metadata corruption: +1
  The bug places an `sg_chain()` marker into the wrong scatterlist entry. This corrupts scatterlist metadata, but the patch does not show an attacker-controlled arbitrary write target or attacker-controlled payload.

* Memory layout invariant restoration: +1
  The fix restores consistency between the actual `sk_msg` scatterlist array size and the count passed to `sg_chain()`. This is a layout/count invariant in networking buffer construction.

* Reliable kernel crash or strong DoS concern: +1
  A malformed scatterlist can later be consumed by the crypto API in the TLS transmit path, making crash or kernel fault a realistic outcome.

* Local high-control kernel data-plane API refinement: +1
  The affected path uses user-driven socket transmit buffers and scatterlist construction. Local users can influence fragmentation and message layout through writes to the socket.

* Paranoid weak LPE concern: +1
  The wrong scatterlist chaining could plausibly cause unintended scatterlist traversal in crypto/networking code. This is not a demonstrated LPE primitive, but it is enough to avoid auto-close and require manual review.

No remote-reachable bonus is applied. The bug is in the TX path and is not a direct packet receive parser issue.

## 3. Reachability analysis

The realistic trigger is local code that can create and write to a kTLS socket and cause a wrapped `sk_msg` scatterlist ring. A remote peer normally cannot directly control the local TX scatterlist ring, although a local network-facing service using kTLS could expose the vulnerable code path through its own local send behavior.

Namespaces do not obviously change the main assessment unless the evaluated product restricts kTLS or requires privileged BPF or sockmap setup for the relevant path. If this path is only reachable through privileged BPF or sockmap in a specific product configuration, the conservative score should be reduced. If ordinary kTLS TX is sufficient, PR is effectively local unprivileged.

Call-site confidence: medium-high. The changed code is inside `tls_push_record()`, and the commit directly explains later crypto API consumption, but the input does not include all sendmsg and crypto call paths.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is an off-by-one scatterlist metadata bug in a networking crypto data path. The conservative interpretation is local DoS with constrained metadata corruption. The paranoid interpretation treats malformed scatterlist traversal as a possible memory-corruption sink, but there is no demonstrated arbitrary write, reclaim primitive, type confusion, or reliable privilege escalation path in the patch.

This should be handled as Actionable Moderate at minimum, not auto-closed. It is not a strong Important candidate without additional evidence of controlled memory corruption or LPE.

## 5. One-sentence report phrase

A local kTLS sender may trigger an off-by-one scatterlist chaining bug when an sk_msg ring wraps, corrupting TLS transmit scatterlist metadata and potentially causing a kernel crash or other unintended crypto API memory access.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because this is a scatterlist off-by-one in the TLS transmit path with plausible memory-corruption consequences beyond a simple warning or resource leak, even though the currently supported evidence is strongest for local DoS rather than proven privilege escalation.

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

Patch: net: tls: fix off-by-one in sg_chain entry count for wrapped sk_msg ring [ Upstream
Commit: 73963a375885d5ccb7def39fd0b4f542e0f343dd
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=73963a375885d5ccb7def39fd0b4f542e0f343dd

Changed files:
  net/tls/tls_sw.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=73963a375885d5ccb7def39fd0b4f542e0f343dd

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

The original Linux kernel CVE announcement for CVE-2026-64047 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64047

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: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: 5
  Paranoid ActionableScore: 6

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).