[CVE-2026-97583][MODERATE 7.0] afs: Clear stale peer app data after address list changes

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

CVE: CVE-2026-97583
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: afs: Clear stale peer app data after address list changes
Commit: 3afb988fd0411707bdafb9b321086fff0da28aae
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3afb988fd0411707bdafb9b321086fff0da28aae
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97583
Analysis date: Fri, 25 Sep 2026 12:47:58 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A stale RxRPC peer association can expose a freed AFS server to remotely initiated callback processing, causing a confirmed kernel use-after-free and potential host denial of service with unresolved post-free object-processing leverage.

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

The original Linux kernel CVE announcement for CVE-2026-97583 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97583

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 7.0
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-2026-97583	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97583 CHECK WITH IMPACT FROM ORIG NN NONE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'An AFS address list replacement can leave stale RxRPC peer app_data pointing to an afs_server that is later freed through RCU. An incoming callback through a connection that still pins the removed peer can read this stale pointer and pass the freed server object to afs_use_server. KASAN confirms a slab use-after-free in afs_find_server. For the CVSS the PR:N value is used because no account or privilege on the affected host is required when the attacker can send callbacks as a reachable AFS peer or fileserver. The attack is network reachable, although practical exploitation normally requires an existing AFS relationship or control of a trusted or compromised fileserver. AC:H reflects the required address refresh, server destruction, RCU timing, and later callback through the old peer. Impact is at least remote denial of service through a kernel crash. In the paranoid interpretation, later reference handling on the freed object may corrupt a reused slab allocation and could affect confidentiality, integrity, and availability or potentially permit privilege escalation. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)  SKIP CVE-2026-97583 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	READ OOB DISK INIT UAF SKIP HARDWARE LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

## 1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* No floor or cap changed either score. The Floor 5 criteria are independently satisfied by below-host-admin network reachability and nontrivial use of an active structured object after free.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

## 2. Signal breakdown

Conservative signals:

* +2 Real UAF / active lifetime violation. A removed RxRPC peer retains `app_data` pointing to an `afs_server` that is subsequently freed through RCU. An incoming callback then obtains and uses that pointer.
* +2 Network reachability. An AFS peer or fileserver can deliver the incoming RxRPC callback that reaches `afs_rx_new_call()` and `afs_find_server()` without requiring an account or privilege on the affected host. An existing AFS relationship and active deployment are prerequisites.
* +1 Reliable kernel crash / strong DoS. KASAN confirms a slab use-after-free in the RxRPC callback-processing thread. A production kernel can fault or encounter invalid refcount/object state.
* Total: 5.

Additional paranoid signal:

* +1 Structured stale-object exploitation leverage. The stale object is an active `afs_server`, not fixed storage or a cleanup-only context. The callback path passes it to `afs_use_server()`, which under normal AFS lifetime semantics mutates its reference state, and the object remains involved in server lookup and incoming-call processing. The remote peer controls the callback through the stale peer association, although controlled slab reclaim is not established.
* Total: 6.

Repeated release/refcount checks:

* The earlier `afs_put_server()` can end the server lifetime and eventually free it through RCU.
* The exact server pointer survives in `Pold->app_data`.
* The later operation is `afs_use_server()`, a reference acquisition on potentially freed storage, not a second release or decrement.
* The dedicated Concrete repeated release/refcount +1 was not awarded because the patch does not establish a second `put`, `release`, `free`, or equivalent decrement on the exact dangling reference.
* Paranoid repeated-release/refcount leverage +1 was withheld for the same reason.
* Floor 5 applies conceptually because this is below-host-admin active callback processing of a structured stale object, but it did not alter the raw conservative score of 5.

Material non-awards:

* Controlled reclaim or attacker-shaped replacement contents are not demonstrated.
* Arbitrary or directed kernel read/write is not demonstrated.
* Strong LPE leverage +2 is not awarded.
* Confidentiality and integrity points are not awarded merely because reused slab memory could theoretically be affected.
* No additional Availability point is awarded because it would duplicate the same crash consequence.
* No race penalty is applied. The description establishes an ordered lifetime sequence but does not show that the required timing is exceptionally narrow, one-shot, or externally uncontrollable.
* No rarity penalty is applied merely because AFS is less common than mainstream local filesystems.

## 3. Reachability analysis

The security-relevant attacker is a remote AFS peer or fileserver capable of sending a callback through an RxRPC connection that still pins the removed peer. Such an attacker needs no local account, capability, or host-administrator privilege, so `HostAdminRequired=NO`.

The complete sequence requires an affected AFS client with an existing mount or server relationship, an address-list refresh that removes the old peer, destruction and RCU freeing of the associated server, and a later callback through the retained RxRPC peer. Prior administrator deployment of AFS is a prerequisite, but the remote endpoint does not need host administration to execute the final vulnerable callback path.

No user-namespace or network-namespace capability is part of the demonstrated attack model, so `NamespaceScopedPrivilege=NO`. The evidence does not establish an alternative local namespace trigger.

No special hardware is required. The kernel must include and actively use AFS and RxRPC. The flaw involves concurrency and lifetime ordering, but the supplied evidence does not establish a sufficiently narrow or unreliable race to justify a timing penalty. Callback attempts can plausibly be repeated by a malicious or compromised peer.

## 4. Primitive and severity interpretation

The exact primitive is a stale `rxrpc_peer->app_data` pointer to a freed `struct afs_server`. The old peer remains alive because an RxRPC connection pins it, while the referenced server can complete its RCU callback and be freed. A subsequent incoming callback reads the stale association and supplies the freed server to `afs_use_server()`.

This is an active structured-object UAF in normal incoming-call processing. It is not fixed stale storage and is not confined to cleanup or destructor execution. The stale path performs at least an object read and reference-state operation, but controlled reclaim, attacker-selected replacement data, callback-pointer consumption, arbitrary access, or demonstrated privilege escalation are not established.

It is therefore CLASS_B rather than CLASS_A. The demonstrated consequence is kernel UAF and likely crash or DoS. The defensible unresolved consequence is corruption of reused slab state through continued server reference and lookup processing. That possibility warrants Important-vs-Moderate review but does not prove arbitrary read/write or LPE.

`ImportantCandidate=YES` because this is a remotely reachable active-object UAF that escapes the original address-list update and server-destruction layers and reaches later RxRPC callback processing. `AutoDowngradeAllowed=NO` because automatic closure would discard unresolved exploitation leverage from a concrete post-lifetime structured-object use and reference-state mutation.

Operationally, the issue is at least Actionable Moderate. It may qualify as Important if manual source and allocator analysis confirms useful reclaim, persistent post-free processing, or influence over reused `afs_server` fields.

## 5. One-sentence report phrase

A stale RxRPC peer association can expose a freed AFS server to remotely initiated callback processing, causing a confirmed kernel use-after-free and potential host denial of service with unresolved post-free object-processing leverage.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

The UAF is confirmed, network callback reachability is established, and the stale active object reaches reference and server-processing logic, but controlled reclaim and practical privilege-escalation leverage remain unresolved.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: afs: Clear stale peer app data after address list changes
Commit: 3afb988fd0411707bdafb9b321086fff0da28aae
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3afb988fd0411707bdafb9b321086fff0da28aae

Commit description:

afs_fs_probe_fileserver() fetches the current endpoint state under
server->fs_lock, but leaves old_alist as NULL.  Consequently,
afs_set_peer_appdata() treats every address list replacement as initial
setup and only binds the new peers; it never unbinds peers removed from
the old list.

An address refresh can therefore proceed as follows.  CPU 0 replaces
server S's list and drops Pold without clearing Pold->app_data.  The
server destroyer then clears only S's current peers and lets S reach its
RCU callback.  After the callback frees S, CPU 1 handles a callback
through an RxRPC connection that still pins Pold, reads Pold->app_data,
and calls afs_use_server() on the freed object.

KASAN reported:

  BUG: KASAN: slab-use-after-free in afs_find_server+0x3c/0xa0
  Read of size 4 at addr ffff8881013e1af0 by task krxrpcio/7001/74
  Call Trace:
   afs_find_server+0x3c/0xa0
   afs_rx_new_call+0x15c/0x390
   rxrpc_new_incoming_call+0x97c/0x1730
   rxrpc_input_packet.constprop.0+0xd03/0xec0
   rxrpc_io_thread+0x967/0x1640
  Allocated by task 93:
   afs_lookup_server+0x1a7/0x14c0
   afs_alloc_server_list+0x43f/0xb60
   afs_create_volume+0x923/0x1490
   afs_get_tree+0x1c6/0x10a0
  Freed by task 0:
   kfree+0x131/0x3c0
   rcu_core+0x50a/0x1850
  Last potentially related work creation:
   __call_rcu_common.constprop.0+0x71/0xa10
   afs_put_server+0x213/0x2b0

Preserve old->addresses for the peer app-data update so that removed
peers are cleared before the endpoint state is replaced.  Also advance
both cursors when the old and new lists share a peer; activating the
old/new comparison without this would otherwise loop forever on the
shared entry.

Fixes: 40e8b52 ("afs: Use the per-peer app data provided by rxrpc")
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
Signed-off-by: Qi Zhang <marsy12010123@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260902121024.3328255-5-dhowells@redhat.com
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: linux-fsdevel@vger.kernel.org
cc: stable@vger.kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/afs/addr_list.c
  fs/afs/fs_probe.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=3afb988fd0411707bdafb9b321086fff0da28aae

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

The original Linux kernel CVE announcement for CVE-2026-97583 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97583

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.1

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: 6

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).