[CVE-2026-74428][MODERATE REGULAR] rxrpc: Fix double unlock in rxrpc_recvmsg()

[CVE-2026-74428][MODERATE REGULAR] rxrpc: Fix double unlock in rxrpc_recvmsg()

[AL-KERNEL]

CVE: CVE-2026-74428
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: rxrpc: Fix double unlock in rxrpc_recvmsg()
Commit: 8cd8cf3052fff9a4b86b25734f610e4af03786d3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8cd8cf3052fff9a4b86b25734f610e4af03786d3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74428
Analysis date: Sun, 16 Aug 2026 03:23:48 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended
Manual review required: YES

Summary:
A remote RxRPC peer may trigger a double socket-lock release in `rxrpc_recvmsg()` during OOB message handling, causing socket lock state corruption and potential kernel DoS on systems exposing affected AF_RXRPC services.

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

The original Linux kernel CVE announcement for CVE-2026-74428 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74428

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
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CVE-2026-74428	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-765;CWE-667;CWE-362;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.9';DESCR 'A double unlock can occur in rxrpc_recvmsg when OOB message handling releases the RxRPC socket lock and then takes an error path that may release it again. A remote RxRPC peer may influence this path by sending OOB protocol traffic such as challenge related messages to an application that uses AF_RXRPC, although reliable triggering depends on the socket state and application behavior. For the CVSS the PR:N is used because the paranoid network scenario does not require attacker privileges on the target beyond network reachability to the RxRPC endpoint. RxRPC is commonly used by AFS or specialized services and is not usually exposed to the public Internet. Impact is denial of service via socket lock state corruption or kernel warning/crash. No concrete information leak or write primitive is visible, so confidentiality and integrity remain N even in the paranoid score.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended (with actual score 4)  SKIP CVE-2026-74428 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 5800b1cf3fd8 YES  NO NO unknown 	MAYBE	OOB SIMPLEFIX LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended**

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  RxRPC is a network protocol and the affected path is in `rxrpc_recvmsg()` handling OOB protocol messages.
* Reliable kernel crash / strong DoS: +1
  A double `release_sock()` can corrupt socket lock state and may lead to WARN/Oops/crash depending on kernel configuration and runtime path.
* Hard or unreliable race / special state required: -1
  Triggering depends on OOB message handling state and application use of AF_RXRPC.
* Rare AND difficult-to-reach subsystem/configuration: -1
  RxRPC is mainly used by AFS or specialized services and is not commonly Internet-exposed.

Paranoid additional signal:

* Availability impact realistic: +1
  If the affected endpoint is reachable and the bad OOB path is reproducible, the impact can be host-level kernel crash rather than only a local socket failure.

No added signals:

* No generic memory corruption score. This is a double unlock of a socket lock, not a demonstrated UAF, OOB write, double free, or type confusion.
* No privilege escalation score. The patch does not show attacker-controlled reclaim, callback control, arbitrary write, or object replacement.
* No confidentiality or integrity impact. No leak or write primitive is visible.

## 3. Reachability analysis

A remote RxRPC peer may influence the vulnerable path by sending OOB protocol traffic to an application using AF_RXRPC. The most plausible affected deployments are AFS or specialized RxRPC services, not general-purpose TCP/IP services. No local credentials on the target are required in the network scenario, but the target must expose an RxRPC endpoint and enter the relevant OOB handling path.

Namespaces and containers do not materially change the main remote scenario. A local user may be able to create AF_RXRPC sockets depending on configuration, but the stronger concern is remote peer influence against an existing service.

Call-site confidence: medium. The patch shows the exact wrong error label after `release_sock()`, but not the full surrounding error labels and all OOB state transitions.

## 4. Severity interpretation

This behaves more like an actionable Moderate or borderline network DoS than an Important-class vulnerability. The theoretical concern is lock-state corruption from a double unlock, but there is no evidence of a concrete memory corruption primitive suitable for LPE. Realistic impact is denial of service if a reachable RxRPC service can be driven into the bad OOB path.

The conservative score stays low because RxRPC exposure is uncommon and triggering appears state-dependent. The paranoid score is higher because the bug is in a network receive path and can plausibly cause a kernel crash.

## 5. One-sentence report phrase

A remote RxRPC peer may trigger a double socket-lock release in `rxrpc_recvmsg()` during OOB message handling, causing socket lock state corruption and potential kernel DoS on systems exposing affected AF_RXRPC services.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a network protocol receive-path locking bug with possible kernel crash impact, but current evidence does not support memory corruption, privilege escalation, or confidentiality/integrity impact.

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

Patch: rxrpc: Fix double unlock in rxrpc_recvmsg()
Commit: 8cd8cf3052fff9a4b86b25734f610e4af03786d3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8cd8cf3052fff9a4b86b25734f610e4af03786d3

Commit description:

Fix a double unlock in rxrpc_recvmsg() when dealing with OOB messages.

Fixes: 5800b1c ("rxrpc: Allow CHALLENGEs to the passed to the app for a RESPONSE")
Link: https://sashiko.dev/#/patchset/20260609140911.838677-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: stable@kernel.org
Link: https://patch.msgid.link/20260624163819.3017002-4-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=8cd8cf3052fff9a4b86b25734f610e4af03786d3

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

The original Linux kernel CVE announcement for CVE-2026-74428 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74428

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: 3
  Paranoid ActionableScore: 4

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).