[CVE-2026-45998][IMPORTANT] rxrpc: Fix potential UAF after skb_unshare() failure [ Upstream

[CVE-2026-45998][IMPORTANT] rxrpc: Fix potential UAF after skb_unshare() failure [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45998
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: rxrpc: Fix potential UAF after skb_unshare() failure [ Upstream
Commit: e3bf143b1e98fb3d6d9e6825bcd683974d478e8c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3bf143b1e98fb3d6d9e6825bcd683974d478e8c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45998
Analysis date: Wed, 27 May 2026 17:29:03 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-45998 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45998

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.

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

CVE-2026-45998	IMPORTANT	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-416;**CWE-476;CWE-703;CWE-755;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'rxrpc_input_packet() could try to unshare a secure DATA skb early in the receive path. If skb_unshare() failed due to ENOMEM, the parent skb pointer could be cleared or the original skb could be consumed while rxrpc_io_thread() still expected to trace and free it, causing a NULL dereference or UAF-like crash. For the CVSS the PR:N is used because no local privileges are required on the victim when an RXRPC endpoint is reachable. The issue is network reachable in RXRPC deployments, but reliable triggering depends on allocation failure or memory pressure and therefore has AC:H. Impact is primarily denial of service, with limited confidentiality and integrity concern kept only for the paranoid score because the bug involves skb lifetime handling in a network receive path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) 	MAYBE	INIT TRACE UAF SKB LINUS PACKET  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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

ActionableScore=7
ActionableScoreLower=5

1. ActionableScore
* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

2. Signal breakdown
* Remote reachable / network-triggerable: +2. The affected path processes RXRPC packets from the network when an RXRPC endpoint is exposed.
* Real lifetime corruption: +1. The old code could let `skb_unshare()` consume or replace the skb and NULL out the parent pointer while the parent still expected to use it.
* Weak memory corruption / UAF candidate: +1. The described failure is NULL dereference or UAF-like skb lifetime misuse, but no controlled reclaim primitive is shown.
* Reliable kernel crash / strong DoS: +1. The parent `rxrpc_io_thread()` can oops in `trace_rxrpc_rx_done()` or cleanup after the pointer is NULL or consumed.
* Availability impact realistic: +1. Kernel crash or RXRPC receive path failure is the main practical impact.
* Common networking receive-path concern: +1. RXRPC is not universal, but this is still packet receive-path skb lifetime handling.
* Hard condition: -1. Reliable triggering depends on `skb_unshare()` allocation failure or memory pressure, so AC is high.

3. Reachability analysis
A remote peer can deliver secure RXRPC DATA packets to the receive path if RXRPC is enabled and reachable. No local privileges are required on the victim. Practical exploitation is harder because the dangerous branch depends on allocation failure during skb unshare, usually requiring memory pressure or constrained allocation conditions. Containers do not materially change the remote network trigger, but host exposure depends on RXRPC/AFS usage and firewalling.

4. Severity interpretation
This is stronger than a simple error-handling DoS because it involves skb ownership/lifetime confusion in a network receive path. The realistic demonstrated impact is kernel oops or DoS. The paranoid interpretation reaches Strong Important candidate because network-triggerable skb lifetime bugs can be underestimated, although the patch does not prove arbitrary write, controlled UAF reclaim, information disclosure, or privilege escalation.

5. One-sentence report phrase
A secure RXRPC DATA packet can hit an `skb_unshare()` failure path that consumes or clears the skb while the receive thread still uses it, causing network-triggerable DoS and a limited UAF-like lifetime concern.

6. Manual review recommendation
MANUAL CHECK REQUIRED. This is network reachable in RXRPC deployments and involves skb lifetime handling after allocation failure, even though reliable exploitation depends on memory pressure and no controlled LPE primitive is shown.

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

Patch: rxrpc: Fix potential UAF after skb_unshare() failure [ Upstream
Commit: e3bf143b1e98fb3d6d9e6825bcd683974d478e8c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3bf143b1e98fb3d6d9e6825bcd683974d478e8c

Changed files:
  include/trace/events/rxrpc.h
  net/rxrpc/ar-internal.h
  net/rxrpc/call_event.c
  net/rxrpc/io_thread.c
  net/rxrpc/skbuff.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=e3bf143b1e98fb3d6d9e6825bcd683974d478e8c

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

The original Linux kernel CVE announcement for CVE-2026-45998 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45998

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:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/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: 7

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).