[CVE-2026-64057][MODERATE 7.0] afs: Fix the locking used by afs_get_link() [ Upstream

[CVE-2026-64057][MODERATE 7.0] afs: Fix the locking used by afs_get_link() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64057
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: afs: Fix the locking used by afs_get_link() [ Upstream
Commit: 77ea917cbed62882a33114b1e23ededb977e4287
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=77ea917cbed62882a33114b1e23ededb977e4287
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64057
Analysis date: Sun, 19 Jul 2026 14:19:15 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
AFS symlink handling lacked proper locking and RCU lifetime protection during get_link() and readlink(), allowing local pathwalk races with server-side symlink updates that may cause stale pointer access, leaks, or kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-64057 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64057

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-2026-64057	MODERATE	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-362;CWE-667;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'AFS symlink handling used insufficient locking around concurrent get_link() and readlink() paths and did not provide proper RCU lifetime protection for symlink buffer pointers during RCU pathwalk. A local user who can access an AFS mounted symlink can trigger repeated path resolution while the symlink contents are refreshed or changed by the server or another client, creating a race with stale pointer access. For the CVSS the PR:L is used because a local user or process is required to exercise the vulnerable filesystem path on the victim system. The issue is not directly Internet reachable, but exposure is higher in AFS deployments where a remote or shared server side actor can update symlink contents while clients traverse them. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to an RCU lifetime bug and possible UAF.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-64057 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: eae9e78951bb02a7b94a9adef6e981413d13c564 YES  NO NO unknown 	MAYBE	LOCK DISK INIT NOMEMCHK RACE LEAK SKIP LINUS  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: **3**
* Paranoid score: **5**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: **+1**. A local user can exercise `get_link()` / `readlink()` / pathwalk on an AFS-mounted symlink.
* Memory corruption, weak or indirect corruption candidate: **+1**. The patch fixes missing RCU protection and stale pointer lifetime handling, but does not show attacker-controlled reclaim, arbitrary write, type confusion, or callback control.
* Real lifetime corruption: **+1**. The fix introduces an RCU-protected `struct afs_symlink` with refcounting, which strongly indicates a real lifetime or stale-pointer problem.
* Reliable kernel crash / strong DoS: **+1**. RCU pathwalk using stale or incorrectly synchronized symlink buffers can plausibly crash the kernel.
* Hard or unreliable race / special timing required: **-1**. Triggering depends on concurrent pathwalk/readlink and symlink refresh/update timing.

Conservative total: **3**

Paranoid additional interpretation:

* Confidentiality impact plausible: **+1**. A stale symlink content pointer used by `readlink()` may plausibly expose stale kernel-backed buffer contents, although no concrete info-leak primitive is demonstrated.
* No LPE bonus awarded. The patch indicates possible UAF/stale pointer behavior, but does not show reclaim control, write-after-free, object replacement, type confusion, callback dispatch, or refcount takeover.

Paranoid total: **5**

Call-site confidence: **high**. The old `afs_get_link()` / `afs_readlink()` behavior and the replacement RCU/refcounted symlink object are visible in the provided patch context.

## 3. Reachability analysis

The bug is reachable by a local user or process that can access an AFS-mounted symlink on the victim system. The most plausible trigger pattern is repeated path resolution or `readlink()` while the symlink contents are being refreshed or changed due to AFS server-side updates. This is not directly Internet-reachable packet parsing, but AFS is a network filesystem, so exposure is higher when the mounted AFS namespace is shared or influenced by another client or server-side actor.

Namespaces do not automatically make this unprivileged everywhere, because the system must already have an AFS mount available. Once mounted and accessible, ordinary local pathwalk operations can exercise the vulnerable path. AFS is not a broad default filesystem on most systems, so exposure is deployment-dependent, but the affected path is a normal filesystem access path rather than an admin-only ioctl.

## 4. Severity interpretation

This behaves more like an **Actionable Moderate** than an ordinary Moderate. The realistic impact is likely local DoS or memory leakage caused by incorrect locking and RCU lifetime handling in AFS symlink access. The theoretical worst case is more concerning because the patch converts symlink storage to a separately allocated RCU-protected and refcounted object, which is a strong indicator of stale pointer or UAF risk.

However, the patch does not demonstrate a strong exploitation primitive such as controlled reclaim, arbitrary write, type confusion, or callback control. Therefore it should not be treated as confirmed Important solely from the diff, but it should not be auto-closed.

## 5. One-sentence report phrase

AFS symlink handling lacked proper locking and RCU lifetime protection during get_link() and readlink(), allowing local pathwalk races with server-side symlink updates that may cause stale pointer access, leaks, or kernel crash.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is a race and RCU lifetime bug in filesystem pathwalk code with possible UAF or stale pointer behavior. The demonstrated primitive is not strong enough to assume reliable privilege escalation, but the lifetime semantics and user-reachable path make it important enough for manual review.

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

Patch: afs: Fix the locking used by afs_get_link() [ Upstream
Commit: 77ea917cbed62882a33114b1e23ededb977e4287
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=77ea917cbed62882a33114b1e23ededb977e4287

Changed files:
  fs/afs/dir.c
  fs/afs/fsclient.c
  fs/afs/inode.c
  fs/afs/internal.h

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=77ea917cbed62882a33114b1e23ededb977e4287

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

The original Linux kernel CVE announcement for CVE-2026-64057 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64057

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:N/I:N/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: 3
  Paranoid ActionableScore: 5

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 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).