[CVE-2026-72330][MODERATE REGULAR] net/tls: Consume empty data records in tls_sw_read_sock() [ Upstream

[CVE-2026-72330][MODERATE REGULAR] net/tls: Consume empty data records in tls_sw_read_sock() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72330
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/tls: Consume empty data records in tls_sw_read_sock() [ Upstream
Commit: 0867b0f2513ebc1c475af9898c97f4772a68d964
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0867b0f2513ebc1c475af9898c97f4772a68d964
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72330
Analysis date: Sat, 15 Aug 2026 23:37:01 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended. Not Important candidate
Manual review required: YES

Summary:
A remote TLS peer can send a valid zero-length TLS 1.3 application data record that causes `tls_sw_read_sock()` to repeatedly requeue the skb and block later records on the same connection, resulting in an availability-only DoS for affected kTLS read_sock users.

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

The original Linux kernel CVE announcement for CVE-2026-72330 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72330

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 REGULAR
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-72330	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';CWE-754;*CWE-835;**CWE-400;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'A remote TLS peer can send a zero length TLS 1.3 application_data record that becomes full_len 0 after decryption in tls_sw_read_sock(). The read_actor has no payload to consume and can return 0, which the old read_sock path treats as backpressure and requeues the skb at the head of rx_list. This blocks all later records on the same connection behind the empty record and can cause a remote denial of service for that connection or for an application relying on the kTLS read_sock path. For the CVSS the PR:N is used because no local account on the target is needed once the attacker can act as a network TLS peer. The issue is network reachable but depends on kTLS and the read_sock receive path, so the base score uses AC:H while the paranoid score uses AC:L. Impact is availability only with no supported evidence of memory corruption, information disclosure, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended. Not Important candidate (with actual score 4)	YES	REMOTE SIMPLEFIX SKB  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: **3**
* Paranoid score: **4**
* Final recommended bucket: **Borderline manual review recommended. Not Important candidate**

## 2. Signal breakdown

Conservative signals:

* **Remote reachable / network-triggerable: +2**
  A remote TLS peer can send a legal zero-length TLS 1.3 `application_data` record.

* **Availability impact realistic: +1**
  The empty record can be requeued at the head of `rx_list`, blocking later records on the same connection and causing a connection/application-level DoS.

* **Common networking/protocol receive path: +1**
  The affected code is in `net/tls`, a network receive path.

* **Rare/configuration-dependent path: -1**
  Practical triggering depends on kTLS and specifically the `tls_sw_read_sock()` path, not ordinary `recvmsg()`.

Paranoid difference:

* The paranoid score does **not** subtract the kTLS/read_sock specificity because, once a service uses this path, the trigger is simple and protocol-valid.

No memory corruption signals apply:

* No UAF.
* No OOB read/write.
* No type confusion.
* No refcount/lifetime corruption.
* No privilege escalation primitive.

## 3. Reachability analysis

A remote peer on a TLS connection can trigger the issue by sending a zero-length TLS 1.3 application data record. No local account is required on the target, so the network trigger is real for services using the affected kTLS read_sock path.

The issue is not universally exposed by all TLS services. It depends on kernel TLS and the `read_sock()` receive path, while `tls_sw_recvmsg()` is explicitly stated not to stall. Namespaces and containers do not materially change the privilege requirement because the attacker is remote and only needs network reachability to the affected service path.

## 4. Severity interpretation

This behaves like an **ordinary to borderline Moderate network DoS**, not an Important-class kernel vulnerability.

The realistic impact is blocking progress on the affected TLS connection or application receive path. There is no evidence of kernel memory corruption, host-wide crash, information disclosure, integrity impact, or privilege escalation. The main reason not to auto-close immediately is network reachability combined with a valid TLS 1.3 input pattern.

## 5. One-sentence report phrase

A remote TLS peer can send a valid zero-length TLS 1.3 application data record that causes `tls_sw_read_sock()` to repeatedly requeue the skb and block later records on the same connection, resulting in an availability-only DoS for affected kTLS read_sock users.

## 6. Manual review recommendation

**MANUAL CHECK RECOMMENDED**

Network reachability makes this worth manual confirmation, but the patch supports only a bounded availability impact and does not show memory corruption or privilege escalation.

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

Patch: net/tls: Consume empty data records in tls_sw_read_sock() [ Upstream
Commit: 0867b0f2513ebc1c475af9898c97f4772a68d964
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0867b0f2513ebc1c475af9898c97f4772a68d964

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=0867b0f2513ebc1c475af9898c97f4772a68d964

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

The original Linux kernel CVE announcement for CVE-2026-72330 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72330

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 5.3

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: 3
  Paranoid ActionableScore: 4

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).