[CVE-2026-97584][MODERATE 7.0] afs: Fix incorrect free in candidate cleanup in afs_lookup_server()

[CVE-2026-97584][MODERATE 7.0] afs: Fix incorrect free in candidate cleanup in afs_lookup_server()

[AL-KERNEL]

CVE: CVE-2026-97584
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: afs: Fix incorrect free in candidate cleanup in afs_lookup_server()
Commit: 981d72663dee2fa6efaf202293e68d2b10a0d1d4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=981d72663dee2fa6efaf202293e68d2b10a0d1d4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97584
Analysis date: Fri, 25 Sep 2026 19:30:28 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97584 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97584

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.

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

CVE-2026-97584	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97584 CHECK WITH IMPACT FROM ORIG NN NONE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'An incorrect free in afs_lookup_server can release endpoint_state belonging to an existing afs_server while that state remains published and reachable through an RCU protected pointer. Later AFS processing may dereference the stale pointer, resulting in a use-after-free, kernel crash, or memory corruption. For the CVSS the PR:L value is used because a local user or process normally needs access to an active AFS mount and must trigger the affected server lookup path. AC:H reflects the specific candidate cleanup state and possible timing or object collision conditions required to free the endpoint state of an existing server. The issue is not proven to be directly reachable from an arbitrary remote network endpoint, although a malicious or compromised AFS service may influence server discovery in an already configured AFS environment. Impact is at least a local denial of service via kernel crash and in the worst case may include confidentiality, integrity, and privilege escalation impact if the freed RCU reachable object is replaced with attacker influenced data.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)  SKIP CVE-2026-97584 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DANGER DISK SKIP LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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

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

1. ActionableScore

* Raw conservative score: 4.
* Conservative score: 5. The active RCU-referenced-object lifetime floor changes 4 to 5.
* Raw paranoid score: 5.
* Paranoid score: 6. The unresolved post-lifetime behavior of an active structured RCU object supports the one-point RCU calibration from 5 to 6.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative positive signals:

* +2 Real UAF / lifetime violation. Candidate cleanup frees `server->endpoint_state` belonging to an existing server while the RCU-published pointer remains installed.
* +1 Concrete RCU referenced-object lifetime mismatch. The existing server remains live and exposes `endpoint_state`, but candidate cleanup directly frees that referenced object without retiring or clearing the published reference.
* +1 Reliable kernel crash / strong DoS. Later use of the stale endpoint state can realistically produce an invalid dereference or allocator-detected UAF.

Paranoid-only signal:

* +1 Unresolved active RCU-reader behavior. `endpoint_state` is an active structured object used by later AFS endpoint processing, and the exact fields consumed after the incorrect free are not visible. This is the specific RCU active-object calibration, not an assumption of controlled reclaim.

Floors and calibration:

* Conservative raw score 4 was raised to 5 by the concrete active-object RCU lifetime rule.
* Paranoid raw score 5 was raised to 6 by the permitted one-point calibration for unresolved processing of an active RCU-referenced object.
* FLOOR 5 was not based on a repeated release. It was based on the concrete RCU lifetime mismatch and continued visibility of active structured state.

Not awarded:

* Controlled reclaim or attacker-shaped replacement contents are not demonstrated.
* Arbitrary or directed kernel read/write is not demonstrated.
* Strong LPE leverage is not awarded merely because this is a UAF.
* Structured stale-object leverage is not separately awarded because attacker influence over reclaimed contents or relevant fields is not established.
* Confidentiality and integrity points are not awarded from theoretical allocator reuse.
* Remote reachability is not established. AFS networking alone does not prove that arbitrary traffic reaches this cleanup state.
* Local-unprivileged-trigger points are withheld because complete below-host-admin reachability is not established.
* No hard-race penalty is applied. The supplied evidence does not establish a narrow or externally uncontrollable timing window.
* No extra Availability point is awarded because the same possible kernel crash is already counted once.

Repeated-release checks:

* The patch does not establish an earlier release followed by a second release of the exact same reference.
* The removed `kfree()` is a single incorrect lifetime-ending operation on the wrong object.
* Concrete repeated release/refcount +1 is not awarded.
* Paranoid repeated-refcount leverage +1 is not awarded.

3. Reachability analysis

The vulnerable operation occurs during AFS server lookup when a temporary candidate is cleaned up after an existing server has been selected. A local process using an already configured AFS mount may cause server lookups, and a configured AFS service may influence the endpoint information involved, but the supplied code does not establish that an ordinary user can force the complete candidate-collision and cleanup sequence.

Host-admin-equivalent privilege is therefore not positively established, but below-host-admin reachability is also incomplete. `HostAdminRequired=UNKNOWN` is appropriate. No namespace capability checks or complete namespace-scoped trigger are shown, so `NamespaceScopedPrivilege=UNKNOWN`.

An AFS mount or cell configuration is likely a practical prerequisite, but the evidence does not establish whether the attacker can create it or merely access an existing mount. No special hardware, boot mode, or proven narrow race is required by the shown fix. Direct arbitrary remote triggering is not established.

4. Primitive and severity interpretation

The exact primitive is an incorrect `kfree()` of an existing server's `endpoint_state` while the server and its RCU-accessible pointer remain live. This directly implies stale post-lifetime access if another AFS path reads the published endpoint state.

The freed object is active structured storage rather than a fixed asynchronous buffer. The erroneous free occurs in cleanup, but its effect escapes cleanup because it corrupts the lifetime of state owned by a different, still-active server. This is therefore CLASS_B rather than a shallow cleanup-only invalid dereference or CLASS_C crash condition.

There is no concrete repeated release or refcount mutation. The bug is also not CLASS_A because controlled reclaim, callback influence, arbitrary read/write, refcount takeover, or demonstrated privilege escalation is absent.

The demonstrated or directly implied consequence is UAF with plausible kernel crash. Memory corruption and privilege escalation remain possible outcomes requiring investigation, but they are not established scoring primitives. `ImportantCandidate=YES` reflects the active RCU-published object and unresolved downstream stale processing. `AutoDowngradeAllowed=NO` is appropriate because automatically treating this as an ordinary cleanup crash would discard a concrete escaping RCU lifetime violation.

Likely operational severity is Actionable Moderate, with Important-class potential depending on the reader call sites, endpoint-state structure, allocator behavior, and attacker control over repeated server lookups.

5. One-sentence report phrase

Candidate cleanup in `afs_lookup_server()` can incorrectly free the RCU-published endpoint state of an existing live server, leaving a stale pointer that may cause a kernel UAF and crash while stronger exploitation consequences require manual analysis.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Review all `endpoint_state` readers, publication and replacement paths, RCU protection, allocator type, and whether an unprivileged AFS client or malicious server can repeatedly drive the candidate cleanup state or influence replacement contents.

7. Call-site confidence

Call-site confidence: medium

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

Patch: afs: Fix incorrect free in candidate cleanup in afs_lookup_server()
Commit: 981d72663dee2fa6efaf202293e68d2b10a0d1d4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=981d72663dee2fa6efaf202293e68d2b10a0d1d4

Commit description:

Fix afs_lookup_server() to not free an existing server's endpoint state
when cleaning up a candidate server.  The candidate record doesn't have an
endpoint state yet at this point, so the free for that can just be removed.

Fixes: 4882ba7 ("afs: Fix afs_server ref accounting")
Link: https://sashiko.dev/#/patchset/20260729160108.2031453-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260902121024.3328255-4-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/server.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=981d72663dee2fa6efaf202293e68d2b10a0d1d4

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

The original Linux kernel CVE announcement for CVE-2026-97584 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97584

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