[CVE-2026-72317][MODERATE 7.0] SUNRPC: pin upper rpc_clnt across the TLS connect_worker [ Upstream

[CVE-2026-72317][MODERATE 7.0] SUNRPC: pin upper rpc_clnt across the TLS connect_worker [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72317
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: SUNRPC: pin upper rpc_clnt across the TLS connect_worker [ Upstream
Commit: 79cd550f8c884523b604fbfa43eb02def74d6224
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=79cd550f8c884523b604fbfa43eb02def74d6224
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72317
Analysis date: Sat, 15 Aug 2026 23:01:45 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A SUNRPC TLS delayed connect worker can dereference a freed upper `rpc_clnt` after a fatal TLS or mTLS handshake failure, allowing a malicious or compromised RPC TLS endpoint to cause a kernel UAF crash when the victim initiates a TLS-secured RPC connection.

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

The original Linux kernel CVE announcement for CVE-2026-72317 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72317

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.

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

CVE-2026-72317	MODERATE	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:R/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A use-after-free can occur in the SUNRPC TLS connect path because xs_connect stores the upper rpc_clnt in sock_xprt clnt as a raw pointer and queues a delayed connect_worker. If a TLS or mTLS handshake fails fatally, the upper rpc_clnt can be released before xs_tcp_tls_setup_socket runs, and the worker can later read freed fields such as cl_timeout, cl_program, cl_cred, and cl_stats. A malicious or compromised RPC TLS server can help trigger the failure condition when the victim initiates a TLS-secured NFS or SUNRPC connection to that endpoint. For the CVSS the PR:N is used because the attacker does not need an account on the victim host in the network server scenario, although the victim must initiate or be configured to initiate the connection. The issue is network reachable in deployments using SUNRPC over TLS, but such services are usually limited to storage or data center networks. Impact is at least denial of service via kernel crash or refcount failure, and in the paranoid case may include confidentiality and integrity impact because the bug class is use-after-free and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	OOB INIT UAF KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Remote reachable / network-triggerable: +2
  A malicious or compromised SUNRPC TLS server can influence the TLS or mTLS handshake failure path after the victim initiates a TLS-secured RPC connection.

* Memory corruption, weak primitive: +1
  This is a real UAF, but the patch shows read access to freed `rpc_clnt` fields from a delayed worker, not a demonstrated attacker-controlled reclaim, overwrite, callback hijack, or type confusion.

* Real lifetime corruption: +1
  The bug is an async lifetime mismatch. `xs_connect()` stores a raw `rpc_clnt` pointer, then `xs_tcp_tls_setup_socket()` may later dereference it after `rpc_shutdown_client()` frees it.

* Reliable kernel crash / strong DoS: +1
  The commit reports a `refcount_t` underflow and UAF symptoms, making kernel crash or serious fault realistic.

Subtracted or limiting signals:

* Hard or unreliable race / special timing required: -1
  The vulnerable window depends on delayed work timing and fatal TLS handshake failure before the worker consumes the saved pointer.

* TLS-secured SUNRPC transport is configuration-dependent: -1 considered for conservative exposure, but not fully applied in the paranoid score because NFS/SUNRPC is a meaningful storage path and TLS use is explicitly supported upstream.

Effective conservative score: 4
Effective paranoid score: 5

## 3. Reachability analysis

The most realistic attacker is a malicious or compromised RPC TLS/NFS server, or an attacker able to make the victim connect to such an endpoint. The attacker does not need a local account on the victim in that scenario, but the victim must initiate or be configured to initiate a TLS-secured SUNRPC connection.

Ordinary NFS mount setup is usually privileged, but automount or preconfigured mounts can make the connection triggerable by less privileged local activity. Containers and namespaces do not generally make arbitrary host NFS TLS mount setup unprivileged, but reduced-privilege service contexts or automount deployments may lower practical trigger requirements.

The path is not a generic public Internet remote attack surface. It is more realistic in storage, data-center, enterprise NFS, or RPC-over-TLS deployments. Call-site confidence: high, because the patch and commit describe the exact async worker, stored pointer, free path, and dereference path.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is a real UAF in a network-influenced SUNRPC TLS path. However, the realistic demonstrated impact is closer to DoS than proven LPE, because the patch does not show controlled reclaim, write-after-free, callback control, or arbitrary memory corruption.

The conservative interpretation is borderline manual-review Moderate. The paranoid interpretation is Actionable Moderate because UAF lifetime bugs in network-influenced kernel paths are historically under-triaged, even when the initial reproducer shows only a crash or refcount failure.

## 5. One-sentence report phrase

A SUNRPC TLS delayed connect worker can dereference a freed upper `rpc_clnt` after a fatal TLS or mTLS handshake failure, allowing a malicious or compromised RPC TLS endpoint to cause a kernel UAF crash when the victim initiates a TLS-secured RPC connection.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real UAF in an async SUNRPC TLS connection path with network-influenced triggering. No strong LPE primitive is demonstrated, but the combination of lifetime corruption, delayed worker dereference, and storage-network exposure should not be auto-closed.

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

Patch: SUNRPC: pin upper rpc_clnt across the TLS connect_worker [ Upstream
Commit: 79cd550f8c884523b604fbfa43eb02def74d6224
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=79cd550f8c884523b604fbfa43eb02def74d6224

Changed files:
  include/linux/sunrpc/clnt.h
  net/sunrpc/clnt.c
  net/sunrpc/xprtsock.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=79cd550f8c884523b604fbfa43eb02def74d6224

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

The original Linux kernel CVE announcement for CVE-2026-72317 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72317

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:R/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 4
  Paranoid ActionableScore: 5

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).