[CVE-2026-74429][MODERATE REGULAR] rxrpc: Fix the reception of a reply packet before data transmission

[CVE-2026-74429][MODERATE REGULAR] rxrpc: Fix the reception of a reply packet before data transmission

[AL-KERNEL]

CVE: CVE-2026-74429
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: rxrpc: Fix the reception of a reply packet before data transmission
Commit: f9be514984471ff0003738b2e1efed12bc3433ff
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f9be514984471ff0003738b2e1efed12bc3433ff
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74429
Analysis date: Sun, 16 Aug 2026 02:25:17 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended because network-triggerable kernel DoS
Manual review required: YES

Summary:
An RxRPC client can oops when it receives an early reply DATA packet before request transmission exposes the call, allowing a malicious peer or packet injector to cause a network-triggerable kernel DoS in affected RxRPC deployments.

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

The original Linux kernel CVE announcement for CVE-2026-74429 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74429

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.

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

CVE-2026-74429	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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:H';*CWE-20;CWE-754;**CWE-476;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'An RxRPC client call can receive an apparent reply DATA packet before request DATA transmission has exposed the call or before the request side has reached a valid transmission state. In that state rxrpc_receiving_reply may enter tx window rotation and rxrpc_rotate_tx_window can oops when the Tx queue is empty or not ready for the requested sequence range, causing a kernel crash. For the CVSS the PR:N is selected for the paranoid score because a remote peer or on path attacker does not need local privileges on the victim when it can inject or send the unexpected RxRPC reply packet. The issue is network reachable for systems using RxRPC based protocols such as AFS, but practical exposure is usually limited to internal storage or distributed filesystem networks and to peers that the client contacts or accepts packets from. Impact is denial of service via kernel oops, with no clear evidence of information disclosure or privilege escalation from the shown code path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended because network-triggerable kernel DoS (with actual score 3)  SKIP CVE-2026-74429 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: b341a0263b1b804d329f864c2dc24815364510ec YES  NO NO unknown 	MAYBE	INIT SIMPLEFIX LINUS PACKET  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended because network-triggerable kernel DoS**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  RxRPC is a network protocol path, and the issue can be triggered by an apparent early reply DATA packet from a peer or packet injector in deployments using RxRPC/AFS-like traffic.
* Reliable kernel crash / strong DoS: +1
  The commit explicitly says `rxrpc_rotate_tx_window()` might oops when the Tx queue is empty or the call has not yet been exposed.
* Rare AND difficult-to-reach subsystem/configuration: -1
  RxRPC is not a broad default Internet-facing protocol path. Practical exposure is usually limited to AFS/RxRPC deployments and peers that the client contacts.

Paranoid adjustment:

* Do not apply the rare-subsystem reduction: +1 relative to conservative
  For triage sensitivity, a network-reachable kernel oops in a protocol receive path should not be auto-closed without review, even if the deployment footprint is limited.

Not awarded:

* Generic memory corruption: +0
  The patch supports invalid/NULL dereference or empty queue handling, not UAF, OOB write, type confusion, double-free, or controlled overwrite.
* Privilege escalation plausible: +0
  No reclaim, object replacement, callback control, write primitive, or refcount abuse is shown.
* Confidentiality / integrity impact: +0
  The demonstrated consequence is an oops/DoS only.

Call-site confidence: high. The patch shows both `rxrpc_receiving_reply()` and the affected `rxrpc_rotate_tx_window()` behavior.

## 3. Reachability analysis

A remote RxRPC peer, malicious server, or on-path packet injector may be able to send an apparent reply DATA packet before the client call has sent request DATA and before `RXRPC_CALL_EXPOSED` is set. No local user privileges on the victim are required for the paranoid network interpretation. The path is not a generic TCP/IP core path and is mainly relevant where RxRPC-based services such as AFS are in use. Namespaces do not materially reduce the network-trigger aspect, but deployment exposure is usually internal or specialized rather than public Internet by default.

## 4. Severity interpretation

This behaves like an actionable network-triggerable Moderate rather than an Important-class memory-corruption issue. The realistic impact is kernel oops or crash through invalid protocol state handling. Theoretical escalation is not supported by the patch because the bug appears to be an invalid dereference / empty Tx queue handling problem, not a reusable UAF or attacker-controlled memory corruption primitive. Because it is network-reachable in affected deployments, it should not be treated as an ordinary auto-closed low-priority DoS without manual review.

## 5. One-sentence report phrase

An RxRPC client can oops when it receives an early reply DATA packet before request transmission exposes the call, allowing a malicious peer or packet injector to cause a network-triggerable kernel DoS in affected RxRPC deployments.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: network-reachable kernel oops in a protocol receive path, even though current evidence supports DoS only and not privilege escalation or confidentiality/integrity impact.

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

Patch: rxrpc: Fix the reception of a reply packet before data transmission
Commit: f9be514984471ff0003738b2e1efed12bc3433ff
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f9be514984471ff0003738b2e1efed12bc3433ff

Commit description:

Fix rxrpc_receiving_reply() to handle the reception of an apparent reply
DATA packet before rxrpc has had a chance to send any request DATA packets
on a client call by checking to see if the call has been exposed yet by
sending the first packet.

Without this, rxrpc_rotate_tx_window() might oops.

Also fix rxrpc_rotate_tx_window() to handle the Tx queue being empty by
changing the do...while loop into a while loop, just in case a call is
abnormally terminated by an early reply before the last request packet is
transmitted.

Fixes: b341a02 ("rxrpc: Implement progressive transmission queue struct")
Link: https://sashiko.dev/#/patchset/20260616155749.2125907-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeffrey Altman <jaltman@auristor.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: stable@kernel.org
Link: https://patch.msgid.link/20260624163819.3017002-7-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/rxrpc/input.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=f9be514984471ff0003738b2e1efed12bc3433ff

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

The original Linux kernel CVE announcement for CVE-2026-74429 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74429

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:L/PR:N/UI:N/S:U/C:N/I:N/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: 2
  Paranoid ActionableScore: 3

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).