* [CVE-2024-53216][MODERATE 7.0] nfsd: release svc_expkey/svc_export with rcu_work [ Upstream
@ 2026-09-28 10:42 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-28 10:42 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2024-53216
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nfsd: release svc_expkey/svc_export with rcu_work [ Upstream
Commit: bd8524148dd8c123334b066faa90590ba2ef8e6f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bd8524148dd8c123334b066faa90590ba2ef8e6f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2024-53216
Analysis date: Mon, 28 Sep 2026 06:42:58 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2024-53216 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2024-53216
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2024-53216 MODERATE https://www.kernelcve.org/list/?q=CVE-2024-53216 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '5.3';DESCR 'A race in the NFSD export cache can reduce the final cache_head reference to zero while c_show or e_show is still reading the object under rcu_read_lock. svc_export_put can then free ex_uuid before svc_export_show finishes using it, resulting in a confirmed read use-after-free. The same release path can call path_put and dput from an RCU read-side critical section even though those operations may sleep. An attacker able to access the affected local procfs cache interface may race a concurrent export cache purge or NFSD shutdown and cause an Oops or kernel crash. The freed ex_uuid contents may also be exposed through the show output, which supports limited confidentiality impact. No write to freed memory or arbitrary write primitive is demonstrated, so privilege escalation is not established. For the CVSS the PR:L value represents the paranoid case where a local user can read the cache interface while a privileged service independently performs the destructive operation. The issue is not directly network reachable because ordinary NFS requests do not invoke the affected procfs show path. Impact is local denial of service with possible limited information disclosure.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5) MAYBE READ DISK INIT UAF NETWORK HARDWARE DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH KPANIC INCREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN5 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap changed either score.
* Final recommended bucket: **Actionable Moderate**::
2. Signal breakdown
Conservative signals:
* +2 Real UAF. `svc_export_put()` can free `ex_uuid` while an RCU-protected `c_show` or `e_show` reader still accesses it. KASAN directly confirms the post-free read.
* +1 Concrete RCU referenced-object lifetime mismatch. The RCU-visible `svc_export` remains available to the reader, but its separately allocated `ex_uuid` is freed before the grace period protecting that reader completes.
* +1 Reliable kernel crash or strong DoS. The confirmed slab UAF can produce an Oops or fatal kernel fault. The suspicious sleeping operation under `rcu_read_lock()` reinforces the invalid execution state but is not scored separately.
* Total: 2 + 1 + 1 = 4.
Additional paranoid signal:
* +1 Plausible confidentiality impact. `svc_export_show()` consumes the freed `ex_uuid` while producing procfs output, providing a technically defensible path for bytes read from reclaimed storage to reach userspace. This is withheld from the conservative score because reuse with sensitive content is not demonstrated.
* Total: 4 + 1 = 5.
Not awarded:
* No local-unprivileged bonus. The demonstrated reader and NFSD teardown writer run as UID 0, and below-host-admin access to the complete sequence is not established.
* No privilege penalty. Host-admin-equivalent privilege for the complete trigger is not positively established.
* No race penalty. A race exists, but the evidence does not establish that repeated attempts are prohibitively narrow or unreliable.
* No structured stale-object leverage. The stale target is the separately allocated UUID storage, and the demonstrated operation is a byte read rather than processing attacker-shaped replacement fields.
* No attacker-controlled reclaim, arbitrary write, callback control, refcount takeover, or controlled type confusion is demonstrated.
* No concrete repeated release or refcount operation exists. The patch does not show the same dangling reference receiving a second lifetime mutation.
* No weak or strong LPE bonus. Privilege escalation would require an additional unproven primitive.
* No extra Availability point. The same UAF crash is counted only once.
* The `path_put()` and `dput()` sleep-under-RCU warning receives no independent point because no separate lasting consequence is established.
Repeated-release checks:
* First release can end the `ex_uuid` lifetime: yes.
* Exact freed reference remains available to a reader: yes.
* Second operation mutates its lifetime or refcount: no. It reads the freed allocation.
* Concrete repeated release or refcount +1: not awarded.
* Paranoid repeated-refcount +1: not awarded.
* FLOOR 5 for repeated lifetime mutation: not applicable.
3. Reachability analysis
The demonstrated sequence requires a local procfs cache reader to overlap with NFSD export-cache purge or server destruction. The supplied trace shows the reader and teardown paths executing as UID 0, but it does not establish that host administration is mandatory for every security-relevant stage. It also does not establish that an ordinary user can read the affected cache interface while a privileged process performs teardown. Therefore, `HostAdminRequired` remains `UNKNOWN`.
No evidence establishes that the complete operation is available through attacker-created user or network namespaces, so `NamespaceScopedPrivilege` is also `UNKNOWN`. NFSD must already be configured and active, which normally implies prior administrative setup, but this prerequisite is not used as a numeric penalty.
Ordinary NFS network requests do not directly invoke the affected procfs show path. Remote reachability is therefore not established. No special hardware is required. The issue is timing-dependent, but the evidence does not characterize the race as sufficiently narrow or uncontrollable to justify a negative point.
4. Primitive and severity interpretation
The exact primitive is a confirmed read use-after-free of the separately allocated `ex_uuid`. An RCU-visible `svc_export` exposes that referenced allocation to a reader after the final cache reference causes `svc_export_put()` to free it. This is a concrete cross-object RCU lifetime mismatch.
The stale allocation is fixed subordinate storage rather than a reclaimed active structured object with attacker-controlled fields. The stale operation reads bytes for export-cache display. It does not write through the stale pointer, invoke callbacks, mutate a refcount, or perform a second release.
This is therefore `CLASS_B`, not `CLASS_A`. Demonstrated consequences are an invalid post-free read, possible Oops or kernel crash, and sleeping from an RCU read-side critical section. A limited userspace disclosure is technically plausible because the read occurs in a procfs show operation, but disclosure of sensitive reclaimed data is not demonstrated.
`ImportantCandidate=NO` because there is no controlled reclaim, write primitive, repeated lifetime mutation, policy bypass, or credible LPE chain. `AutoDowngradeAllowed=YES` because this is a constrained read UAF with primarily crash behavior and only limited unresolved disclosure potential. Manual review remains recommended to confirm procfs permissions, allocation reuse behavior, and whether sensitive bytes can actually be returned.
5. One-sentence report phrase
A premature NFSD export-cache release can free ex_uuid before an RCU-protected procfs reader finishes using it, causing a confirmed read use-after-free with kernel-crash and limited information-disclosure potential.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Confirm access permissions for the affected procfs cache files and whether realistic allocator reuse can expose sensitive data, but no Important-grade exploitation primitive is currently established.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: nfsd: release svc_expkey/svc_export with rcu_work [ Upstream
Commit: bd8524148dd8c123334b066faa90590ba2ef8e6f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bd8524148dd8c123334b066faa90590ba2ef8e6f
Changed files:
fs/nfsd/export.c
fs/nfsd/export.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=bd8524148dd8c123334b066faa90590ba2ef8e6f
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2024-53216 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2024-53216
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:H/UI:N/S:U/C:L/I:N/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H
The Best / paranoid CVSS score: 5.3
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: 4
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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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