[CVE-2026-74431][MODERATE REGULAR] rxrpc: Fix potential infinite loop in rxrpc_recvmsg()

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

CVE: CVE-2026-74431
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: rxrpc: Fix potential infinite loop in rxrpc_recvmsg()
Commit: 0fc5b37faec26241d3cbee732e29ac35ad3184f8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0fc5b37faec26241d3cbee732e29ac35ad3184f8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74431
Analysis date: Sun, 16 Aug 2026 04:33:29 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Borderline network DoS candidate requiring review
Manual review required: NO

Summary:
A network-reachable RXRPC peer may cause `rxrpc_recvmsg()` to make an incorrect wait decision when OOB data is queued, potentially leading to an infinite loop or blocking denial of service on systems exposing RXRPC or AFS-style services.

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

The original Linux kernel CVE announcement for CVE-2026-74431 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74431

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: NO

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-2026-74431	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-835;**CWE-400;CWE-754;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.9';DESCR 'rxrpc_recvmsg() could make an incorrect wait decision because it checked rx.recvmsg_q but did not also check rx.recvmsg_oobq. If an out-of-band RXRPC message is queued while the normal receive queue is empty, the recvmsg path can enter a potential infinite loop or blocking condition and cause denial of service. For the CVSS the PR:N is selected because a remote peer may trigger the protocol state without local privileges when an RXRPC service is reachable. The issue is network reachable only for systems exposing RXRPC or AFS style services to the attacker. Impact is availability only. No memory corruption, information disclosure, or privilege escalation primitive is indicated by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Borderline network DoS candidate requiring review (with actual score 3)  SKIP CVE-2026-74431 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 5800b1cf3fd8 YES  NO NO unknown 	MAYBE	OOB SIMPLEFIX SKB IMPROVEONLY LINUS  LOWERED_FROM_HIGH_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: **Ordinary Moderate / Borderline network DoS candidate requiring review**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  RXRPC is a network protocol, and the affected state involves OOB protocol messages such as CHALLENGE handling. A remote peer may influence this path if an RXRPC or AFS-style service is reachable.
* Reliable kernel crash / strong DoS: +1
  The commit describes a potential infinite loop in `rxrpc_recvmsg()`. This is availability-impacting, but the patch does not show memory corruption or a direct host-wide crash.
* Rare AND difficult-to-reach subsystem/configuration: -1
  RXRPC/AFS exposure is not a common public-facing default on most systems.

Paranoid adjustment:

* Availability impact realistic: +1
  In the higher-bound interpretation, a stuck `recvmsg()` path in a reachable service could cause a meaningful service-level DoS, especially if worker threads are exhausted or repeatedly trapped.

No memory-corruption signals apply:

* No UAF, double-free, OOB write, type confusion, refcount takeover, stale callback, arbitrary write, or page-cache/shared-page corruption is indicated by the patch.
* No confidentiality or integrity impact is supported.

## 3. Reachability analysis

A remote RXRPC peer may trigger the problematic OOB queue condition if the target exposes RXRPC or AFS-related services. No local privileges are needed in that network-facing deployment model, so PR:N is reasonable for CVSS-style reachability. However, RXRPC is not a broad default Internet-exposed protocol, and practical exposure depends on whether such services are enabled and reachable. Containers and namespaces do not materially improve reachability unless they expose or consume RXRPC services.

Call-site confidence: medium. The patch directly changes `rxrpc_recvmsg()`, but only a small local diff is provided, so the assessment relies on RXRPC receive-path semantics and the commit description.

## 4. Severity interpretation

This behaves like an ordinary Moderate or borderline actionable Moderate network DoS, not an Important-class kernel vulnerability. The realistic impact is service or kernel-path availability degradation through an infinite loop or blocking condition. Theoretical escalation is not supported because there is no demonstrated memory corruption primitive, no stale object reuse, and no attacker-controlled write or disclosure path.

## 5. One-sentence report phrase

A network-reachable RXRPC peer may cause `rxrpc_recvmsg()` to make an incorrect wait decision when OOB data is queued, potentially leading to an infinite loop or blocking denial of service on systems exposing RXRPC or AFS-style services.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the bug appears to be DoS-only and has no memory-corruption primitive, but the affected path is potentially network reachable in RXRPC/AFS deployments, so it should not be blindly auto-closed without checking product exposure.

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

Patch: rxrpc: Fix potential infinite loop in rxrpc_recvmsg()
Commit: 0fc5b37faec26241d3cbee732e29ac35ad3184f8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0fc5b37faec26241d3cbee732e29ac35ad3184f8

Commit description:

Fix the wait in rxrpc_recvmsg() also take check the oob queue.

Fixes: 5800b1c ("rxrpc: Allow CHALLENGEs to the passed to the app for a RESPONSE")
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/20260624163819.3017002-9-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/rxrpc/recvmsg.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=0fc5b37faec26241d3cbee732e29ac35ad3184f8

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

The original Linux kernel CVE announcement for CVE-2026-74431 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74431

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:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.9

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).