* [CVE-2026-98624][IMPORTANT] netfilter: nfnetlink_queue: hold nfnl mutex in event notifier [ Upstream
@ 2026-10-24 0:01 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 0:01 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98624
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: netfilter: nfnetlink_queue: hold nfnl mutex in event notifier [ Upstream
Commit: 46432f2e76f7c385d82506304a2928e7d293289f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=46432f2e76f7c385d82506304a2928e7d293289f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98624
Analysis date: Fri, 23 Oct 2026 20:01:12 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A race between NFQUEUE UNBIND processing and NETLINK_URELEASE can destroy the same unrefcounted queue instance while a stale pointer remains active, causing a kernel fault and leaving unresolved post-lifetime destruction corruption that requires manual review.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98624 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98624
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: IMPORTANT
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-2026-98624 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-98624 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC) 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-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in nfnetlink_queue can allow the NETLINK_URELEASE notifier to destroy an NFQUEUE instance while a concurrent UNBIND request is still processing the same object after its RCU read lock was dropped. The observed result is a general protection fault in __instance_destroy, and the lack of instance reference counting makes stale object access or a use after free a plausible memory corruption condition. For the CVSS the PR:L value is used because reliable triggering requires local access to the NETFILTER netlink configuration path, normally through CAP_NET_ADMIN, but this capability can be delegated to a container root or a restricted network service without granting full host administration. AC:H is used because successful triggering depends on winning the race between socket close and UNBIND processing. The issue is not directly reachable through ordinary network packets because local netlink control operations are required. Impact is at least a local denial of service through a kernel fault. In the paranoid case the object lifetime violation may permit confidentiality or integrity impact through memory corruption and should be reviewed manually. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 6 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and TEMP_KPANIC_MERGE_IMPORTANT_WINS. The independent weaker Aegis shadow evaluated CVSS 3.1 and ActionableScore 5 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) MAYBE REMOTE SIMPLEFIX NETFILTER LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS TEMP_KPANIC_MERGE_IMPORTANT_WINS - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=YES
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
## 1. ActionableScore
* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* No cap changed either score. The REAL UAF FLOOR 5 applies but does not change the conservative result.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
## 2. Signal breakdown
### Conservative signals
* **+2 Real UAF or lifetime violation:** `nfqnl_recv_config()` retains an NFQUEUE instance pointer after dropping its RCU read lock. Concurrent `NETLINK_URELEASE` processing can destroy that instance before the configuration path finishes using it.
* **+1 Concrete repeated lifetime operation:** the release notifier can call `__instance_destroy()` for the instance, while the concurrent `UNBIND` path can subsequently call the same destructor through its stale queue pointer. This is more than a passive stale read.
* **+1 Reliable kernel crash:** the commit supplies an observed general protection fault in `__instance_destroy()`.
* **+1 Attacker-influenced lifetime manipulation:** an actor with NFQUEUE configuration access can create the relevant state and repeatedly race an `UNBIND` request against closing the associated netlink socket.
Total: **2 + 1 + 1 + 1 = 5**.
### Paranoid addition
* **+1 Unresolved post-lifetime mutation:** the second `__instance_destroy()` is not established as a guaranteed fault before making changes. It can operate on an instance whose logical lifetime has ended and may repeat list removal or destruction operations against stale storage.
Total: **5 + 1 = 6**.
### Signals not awarded
* Controlled reclaim or attacker-shaped replacement contents are not demonstrated.
* Arbitrary or directed kernel read or write is not demonstrated.
* Callback or function-pointer control is not demonstrated.
* Confidentiality impact, integrity impact, and privilege escalation are not established.
* No remote-reachability point is awarded because ordinary packets cannot invoke the vulnerable control-plane sequence.
* No local-unprivileged point is awarded because availability of attacker-created user and network namespaces is product dependent.
* No race penalty is applied because both operations can be driven repeatedly and the evidence does not establish a narrow one-shot window.
* No extra availability point is awarded for the same kernel fault.
* Structured stale-object leverage is not separately awarded because the relevant evidence is already counted as a concrete repeated destruction operation.
* Weak LPE is not separately awarded for the same lifetime mutation.
### Repeated-lifetime checks
* First operation can end lifetime: **Yes**. The notifier calls `__instance_destroy()`.
* Exact reference survives: **Yes**. The configuration path retains the pointer obtained under RCU after dropping the read lock.
* Second operation mutates lifetime or destruction state: **Yes**. The concurrent `UNBIND` path enters `__instance_destroy()` again.
* Concrete repeated release point awarded: **Yes, +1**.
* Paranoid post-lifetime mutation point awarded: **Yes, +1**.
* FLOOR 5 applied: **Yes, with no numerical change**.
## 3. Reachability analysis
The trigger requires local `NETLINK_NETFILTER` control-plane operations, specifically a concurrent NFQUEUE `UNBIND` and socket close producing `NETLINK_URELEASE`. It is not directly reachable through incoming network traffic.
NFQUEUE configuration normally requires `CAP_NET_ADMIN` for the target network namespace. That authority can be held by container root or a delegated network-management service without host-administrator powers. The affected instances are per-network-namespace state, so the complete operation is namespace scoped when the actor controls that namespace.
No host UID 0 requirement is inherent to the interface. An ordinary user can reach this model only where user and network namespace creation is permitted, so ordinary-unprivileged reachability is not assumed for scoring. No special hardware, boot mode, or unusual device is required.
The race appears repeatable because the same actor can issue configuration messages and close sockets in parallel. The supplied evidence does not establish that the timing window is exceptionally narrow or uncontrollable.
## 4. Primitive and severity interpretation
The exact primitive is a race-induced stale use of an active, structured NFQUEUE instance. RCU protects the lookup initially, but the configuration path drops the RCU read lock before completing its use. The notifier may then destroy the instance concurrently.
This is category B from the repeated-lifetime distinction:
1. The notifier destroys the instance.
2. The configuration path retains the same pointer.
3. The `UNBIND` path invokes the destructor through that stale pointer.
4. The second destructor can mutate list or object-lifetime state after the first destruction.
Therefore this is **CLASS_B**, not merely a CLASS_C invalid dereference. It is not CLASS_A because controlled reclaim, directed corruption, arbitrary access, or another strong exploitation primitive is not established.
The demonstrated consequence is a host kernel fault and denial of service. More useful post-free corruption is unresolved but not proven. `ImportantCandidate=YES` and `AutoDowngradeAllowed=NO` are appropriate because the stale path performs a concrete second destruction operation rather than only reading an invalid pointer.
B4 authorization-state rules do not apply. No authorization decision changes from DENY to ALLOW, and no protected resource access is implicated.
## 5. One-sentence report phrase
A race between NFQUEUE UNBIND processing and NETLINK_URELEASE can destroy the same unrefcounted queue instance while a stale pointer remains active, causing a kernel fault and leaving unresolved post-lifetime destruction corruption that requires manual review.
## 6. Manual review recommendation
MANUAL CHECK REQUIRED
The confirmed stale active-object use includes a concrete second destruction operation, while the exploitation value of the resulting post-lifetime mutations is unresolved.
## 7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: netfilter: nfnetlink_queue: hold nfnl mutex in event notifier [ Upstream
Commit: 46432f2e76f7c385d82506304a2928e7d293289f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=46432f2e76f7c385d82506304a2928e7d293289f
Changed files:
net/netfilter/nfnetlink_queue.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=46432f2e76f7c385d82506304a2928e7d293289f
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98624 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98624
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: 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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT
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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