[CVE-2026-64026][IMPORTANT] rxrpc: Fix DATA decrypt vs splice() by copying data to buffer in recvmsg [ Upstream

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

CVE: CVE-2026-64026
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: rxrpc: Fix DATA decrypt vs splice() by copying data to buffer in recvmsg [ Upstream
Commit: a05bf6d9e621fa71e89ccebe3047ba45218d7b38
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a05bf6d9e621fa71e89ccebe3047ba45218d7b38
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64026
Analysis date: Sun, 19 Jul 2026 12:42:41 -0400
ActionableScore: 8
ActionableScore lower bound: 7
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
RxRPC in-place decryption of locally spliced encrypted DATA packets can corrupt shared page-cache-backed skb data, creating a local integrity primitive with plausible privilege-escalation relevance rather than a simple DoS.

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

The original Linux kernel CVE announcement for CVE-2026-64026 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64026

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
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CVE-2026-64026	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN LOW	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-471;CWE-668;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L';BEST CVSS score: '7';DESCR 'rxrpc can corrupt pagecache data because encrypted DATA packets sent locally through splice can share storage with the source page cache, and recvmsg previously decrypted packet contents in place inside the sk_buff. A local attacker who can create rxrpc traffic and use splice may cause the receive path to modify shared page cache pages instead of a private receive buffer. For the CVSS the PR:L is used because reliable triggering requires local code execution by an unprivileged user or service account rather than pure network reachability. The issue is not a normal remote network bug, because the dangerous sharing comes from local splice based transmit paths. Impact is at least local data integrity corruption and denial of service, and in the worst defensible case pagecache corruption may affect data later consumed by more privileged processes and may support privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8)	YES	INIT WARNONLY NOMEMCHK SKB IMPROVEONLY LINUS PACKET  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	YES	NO	checked

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

ActionableScore=8
ActionableScoreLower=7

## 1. ActionableScore

* Conservative score: 7
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  A local user or service can potentially create RxRPC traffic and use splice() to produce shared skb/page-cache backing.

* Shared page-cache corruption / Dirty-Pipe-like ownership violation: +3
  The core primitive is in-place decryption into skb data that may share storage with page-cache pages from splice(). This is not ordinary metadata corruption. It can modify externally owned file-backed pages without normal COW or permission expectations.

* Privilege escalation plausible: +2
  Page-cache corruption can potentially affect data later consumed by a more privileged process. This is not a proven LPE chain, but it is a strong enough primitive to require Important-class triage.

* Integrity impact plausible: +1
  The commit explicitly describes pagecache corruption.

* Availability impact realistic: +1
  Corrupted page-cache contents can cause application misbehavior, data corruption, or denial of service beyond a simple transient warning.

* Important filesystem/storage/page-cache path: +1
  The affected behavior crosses networking, splice, skb fragments, and page-cache-backed memory.

* Requires special conditions: -1
  Reliable triggering appears to require RxRPC usage, local splice-based transmission, and encrypted DATA handling.

* Less common subsystem exposure: -1
  RxRPC/AFS is less broadly exposed than TCP/IP or netfilter, though the primitive itself is high risk.

## 3. Reachability analysis

The most realistic trigger is local. The dangerous condition comes from DATA packets transmitted locally through splice(), where skb fragments can remain backed by page-cache memory. This is not a normal remote network-triggered RxRPC parsing issue, because the ownership violation depends on local splice/page-cache sharing.

A fully unprivileged user may be able to reach relevant socket and splice paths depending on kernel configuration and RxRPC availability. Namespaces or containers may matter if the workload can create RxRPC sockets and access files suitable for splice(). The path is not as broadly exposed as common TCP/IP receive code, but it involves high-value shared page-cache semantics and therefore should not be treated as a routine niche DoS.

Call-site confidence: high. The patch shows the receive path moving from skb in-place verification/decryption to a per-call bounce buffer, and the commit explicitly states that this fixes pagecache corruption.

## 4. Severity interpretation

This behaves more like an Important candidate than an ordinary Moderate issue. The realistic demonstrated impact is local page-cache corruption caused by in-place crypto on shared skb-backed data. The theoretical worst case is stronger because page-cache corruption can bypass normal file ownership or COW assumptions and may influence data later read or executed by privileged processes.

There is no evidence of a direct arbitrary kernel write or proven code execution chain in the patch. However, page-cache/shared-page corruption is historically high-risk and should be manually reviewed even if practical exploitation depends on RxRPC and splice-specific conditions.

## 5. One-sentence report phrase

RxRPC in-place decryption of locally spliced encrypted DATA packets can corrupt shared page-cache-backed skb data, creating a local integrity primitive with plausible privilege-escalation relevance rather than a simple DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is required because the primitive is page-cache/shared-page corruption with Dirty-Pipe-like ownership implications. Even without a demonstrated exploit chain, the bug can affect data outside the intended private receive buffer and may cross privilege or file-permission boundaries.

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

Patch: rxrpc: Fix DATA decrypt vs splice() by copying data to buffer in recvmsg [ Upstream
Commit: a05bf6d9e621fa71e89ccebe3047ba45218d7b38
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a05bf6d9e621fa71e89ccebe3047ba45218d7b38

Changed files:
  net/rxrpc/ar-internal.h
  net/rxrpc/call_event.c
  net/rxrpc/call_object.c
  net/rxrpc/insecure.c
  net/rxrpc/recvmsg.c
  net/rxrpc/rxkad.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=a05bf6d9e621fa71e89ccebe3047ba45218d7b38

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

The original Linux kernel CVE announcement for CVE-2026-64026 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64026

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:H/A:L
  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: 7
  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: 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).