[CVE-2026-74610][MODERATE 7.0] tls: don't leave a full plaintext sk_msg ring unpushed

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

CVE: CVE-2026-74610
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: tls: don't leave a full plaintext sk_msg ring unpushed
Commit: aa8b14647721b5a4958712b35cf43e3125d47753
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aa8b14647721b5a4958712b35cf43e3125d47753
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74610
Analysis date: Sat, 22 Aug 2026 17:32:05 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local unprivileged user can trigger corrupted TLS `sk_msg` scatterlist ring state via sendmsg and splice on a TCP socket with the `tls` ULP, causing a reliable kernel crash and requiring manual review due to possible memory corruption beyond DoS.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74610 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74610

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-2026-74610	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-20;*CWE-787;**CWE-476;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.8';DESCR 'A local user can trigger a NULL pointer dereference in the TLS software send path because a full plaintext sk_msg ring may be left unpushed after sendmsg() copy processing. A later splice() can append data to the already full ring, causing sg.end to wrap to sg.start, live scatterlist entries to be overwritten, and sg.size to no longer match the reachable ring contents. When the record is pushed, scatterwalk can run past the valid scatterlist and crash the kernel in the crypto path. For the CVSS the PR:L value is used because triggering requires local code execution by an unprivileged user with access to a TCP socket using the tls ULP, not administrative privileges. The issue is not directly network reachable because the attacker must run local code on the target, although loopback sockets are sufficient. Impact is at least local denial of service via kernel crash. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual-review sensitivity over autoclosed false negatives. The corrupted sk_msg scatterlist state and out of bounds scatterwalk make limited or full confidentiality and integrity impact worth manual review even though the demonstrated crash is DoS.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8)  SKIP CVE-2026-74610 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	REMOTE NULLPTR BPF LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. The commit explicitly states that an unprivileged user can trigger this on a loopback TCP socket with the `tls` ULP attached.
* Memory corruption, weak or constrained corruption candidate: +1. The demonstrated outcome is a NULL pointer dereference, but the bug involves `sg.end` wrapping and live scatterlist entries being overwritten.
* Memory layout invariant restoration: +1. The fix restores consistency between `sk_msg` ring fullness, `sg.start`, `sg.end`, `sg.size`, and record push state in the TLS send path.
* Reliable kernel crash / strong DoS: +1. The commit includes a concrete kernel NULL dereference trace in the crypto scatterwalk path.
* Local unprivileged high-control kernel data-plane API: +1. The trigger uses local socket operations, `sendmsg`, `splice`, TLS ULP, and scatterlist construction with fine-grained user influence over buffer state.
* Common networking / splice adjacent path: +1. This is in `net/tls` and interacts with ordinary TCP socket send paths and splice-style page handling.

Paranoid additional interpretation:

* Memory corruption upgraded to strong primitive: +1 over conservative. The patch context says fragments overwrite live entries and scatterwalk runs off the end of the scatterlist, which is stronger than a pure NULL dereference.
* Weak LPE concern: +1. There is no demonstrated arbitrary write or reclaim primitive, but corrupted scatterlist metadata in a local high-control data path is enough to require manual review for possible confidentiality or integrity impact.

Not counted:

* Remote reachable: +0. The issue is local, not packet-triggered from the network.
* Real lifetime corruption: +0. No UAF, double-free, stale callback, or refcount takeover is shown.
* Availability impact realistic: not double-counted separately because reliable crash was already counted.

## 3. Reachability analysis

A local unprivileged process can trigger the bug if kernel TLS support is available and the process can create a TCP socket with the `tls` ULP attached. The commit states that loopback is sufficient, so no external network peer is required. This is not realistically remote-triggerable by ordinary inbound packets.

Namespaces or containers may matter because a containerized unprivileged process that can use the relevant socket and TLS ULP path could potentially crash the host kernel, depending on product configuration and kernel TLS availability. The path is not necessarily active by default for every socket, but it is reachable through ordinary local networking APIs when kTLS is enabled.

## 4. Severity interpretation

This is more than an ordinary Moderate DoS because the failure is not just validation or resource exhaustion. The bug corrupts internal `sk_msg` scatterlist ring state, overwrites live entries, and then drives scatterwalk beyond the valid scatterlist boundary.

Realistically demonstrated impact is local kernel crash. Theoretical higher impact is plausible enough for manual review because the corrupted object is scatterlist metadata in a high-control local data path, but the patch does not prove arbitrary write, controlled object replacement, UAF reclaim, or reliable privilege escalation.

## 5. One-sentence report phrase

A local unprivileged user can trigger corrupted TLS `sk_msg` scatterlist ring state via sendmsg and splice on a TCP socket with the `tls` ULP, causing a reliable kernel crash and requiring manual review due to possible memory corruption beyond DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the issue is locally unprivileged, has a demonstrated kernel crash, and the patch context explicitly describes overwritten live scatterlist entries plus scatterwalk running past valid state. Even if the proven impact is DoS, the memory corruption characteristics make auto-closure unsafe.

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UPSTREAM PATCH SUMMARY
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Patch: tls: don't leave a full plaintext sk_msg ring unpushed
Commit: aa8b14647721b5a4958712b35cf43e3125d47753
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aa8b14647721b5a4958712b35cf43e3125d47753

Commit description:

When the copy path in tls_sw_sendmsg_locked() adds the fragment that fills
the plaintext sk_msg ring, it does not set full_record, so the record is
left full and unpushed.  A later splice() then adds to an already full
ring: sk_msg_page_add() has no fullness check of its own, so sg.end wraps
onto sg.start and the ring appears empty.  Fragments added after that
overwrite live entries, and sg.size no longer matches what is reachable
between sg.start and sg.end, so pushing the record runs the scatterwalk off
the end of the scatterlist.

An unprivileged user can trigger this on a loopback TCP socket with the
"tls" ULP attached:

  BUG: kernel NULL pointer dereference, address: 0000000000000008
  RIP: 0010:memcpy_from_scatterwalk+0x32/0xc0
  Call Trace:
   skcipher_walk_next+0x1d1/0x2c0
   gcm_encrypt_aesni_avx+0x1e9/0x220
   bpf_exec_tx_verdict+0x3bb/0x860
   tls_sw_sendmsg+0xa1a/0xca0
   __sys_sendto+0x1da/0x1f0

Set full_record in the copy path when the ring becomes full, and push a
record that is already full on entry to the sendmsg loop.

Suggested-by: Sabrina Dubroca <sd@queasysnail.net>
Fixes: fe1e81d ("tls/sw: Support MSG_SPLICE_PAGES")
Cc: stable@vger.kernel.org
Signed-off-by: chanyoung <ppoo1220@gmail.com>
Link: https://patch.msgid.link/20260804052837.49015-2-ppoo1220@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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=aa8b14647721b5a4958712b35cf43e3125d47753

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

The original Linux kernel CVE announcement for CVE-2026-74610 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74610

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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 6
  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: 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).