* [CVE-2026-99054][IMPORTANT] tipc: destroy topsrv workqueues before closing connections
@ 2026-10-27 6:37 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-27 6:37 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99054
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: tipc: destroy topsrv workqueues before closing connections
Commit: 7f796bb3b440d7f1b14c0e3b520462eb34f553af
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7f796bb3b440d7f1b14c0e3b520462eb34f553af
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99054
Analysis date: Tue, 27 Oct 2026 02:37:34 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
TIPC topology-server teardown can race with active callbacks and workers, causing zero-ref connection resurrection, a confirmed connection UAF, destroyed-workqueue submission, and host-kernel DoS.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99054 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99054
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-99054 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-99054 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT IMPORTANT AEGIS_AS=4 LEGACY=IMPORTANT RESULT=SAME INDEPENDENT_LEGACY=MODERATE_KPANIC INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=MODERATE_KPANIC (final reconciliation agrees; DECISION: both IMPORTANT) 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-672;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in TIPC topology server teardown allowed connections to be closed while send and receive workqueues were still active. In flight work and socket callbacks could race with the conn_idr walk and cause refcount resurrection, a confirmed use after free in tipc_conn_close, queue_work on a destroyed workqueue, or an RCU stall. For the CVSS the PR:L value reflects that reliable triggering normally requires a local user or process able to use TIPC and initiate network namespace or topology server teardown. AC:H reflects the need to hit a teardown timing window with active callbacks or subscription events. The issue is not proven to be remotely triggerable by TIPC traffic alone, although an adjacent TIPC peer may contribute concurrent activity. Impact is at least a local denial of service and the confirmed use after free provides a plausible kernel memory corruption path, so the paranoid assessment includes potential confidentiality and integrity impact. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because FD false positive review allowed a downgrade. final reconciliation stage MODERATE_KPANIC to IMPORTANT because KP specialist did not establish a qualifying panic. 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 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH and TEMP_KPANIC_MERGE_IMPORTANT_WINS and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was IMPORTANT. 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 5) MAYBE LOCK TIPC RACE UAF LINUS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH TEMP_KPANIC_MERGE_IMPORTANT_WINS KPANIC_UNSUPPORTED_REMOVED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 4.
* Conservative score: 4; no floor or cap changed it.
* Raw paranoid score: 5.
* Paranoid score: 5; no floor or cap changed it.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 Real UAF/lifetime violation: in-flight work can drop the final connection reference while teardown retains and later uses the connection; the commit confirms UAF in `tipc_conn_close()`.
* +1 Reliable kernel crash/strong DoS: destroyed-workqueue queueing, UAF, refcount failure, and RCU stall plausibly cause host failure.
* +1 Active structured/refcount leverage: `conn_get()` can attempt refcount resurrection from zero, followed by connection teardown processing.
* +1 Attacker-influenced lifetime sequence: active connections, callbacks/subscription events, and teardown jointly drive the vulnerable transition.
* -1 Hard timing: the supplied evidence explicitly requires a teardown window with in-flight callbacks or subscription work.
* Paranoid +1: a separate shown post-retirement consumer can call `queue_work()` on an already destroyed workqueue, leaving active corrupted-state consumption beyond the initial stale connection use.
No controlled reclaim, arbitrary write, callback-pointer control, disclosure, or LPE is shown. C/I points are not awarded. The same crash receives no additional Availability point. This is not the dedicated repeated-release case: the shown exceptional mutation is `kref_get`/refcount addition on zero, not a proven second `put` on the exact dangling reference; therefore no repeated-release bonus or floor 5 was applied.
3. Reachability analysis
The supplied summary grounds a local TIPC-capable actor contributing connections/events and initiating topology-server or network-namespace teardown, but does not establish the exact capability checks or prove that the complete trigger is available to an ordinary user. Thus host-admin and full namespace-scoped reachability remain unknown. Remote TIPC traffic alone is not proven sufficient. No special hardware is required. The timing race is explicitly high-complexity.
4. Primitive and severity reading
This is an active structured connection lifetime violation, not fixed stale storage. Teardown races with send/receive workers and socket callbacks; the resulting zero-ref resurrection, later `tipc_conn_close()` UAF, and destroyed-workqueue submission are specifically shown. The proven effect is crash/stall-capable host-kernel invalid-state consumption. Exploit-grade reuse or directed corruption remains unproven.
A credible user/netns-to-more-privileged-host-kernel boundary exists but its complete privilege mechanics are unresolved. Under the active-state trust-boundary rule, this supports `ImportantCandidate=YES`, mandatory review, and no automatic downgrade without claiming proven Important severity.
5. One-sentence report phrase
TIPC topology-server teardown can race with active callbacks and workers, causing zero-ref connection resurrection, a confirmed connection UAF, destroyed-workqueue submission, and host-kernel DoS.
6. Manual review advice
MANUAL CHECK REQUIRED
Review complete namespace privilege, trigger repeatability, stale connection field consumption, and whether refcount resurrection permits useful post-lifetime corruption.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: tipc: destroy topsrv workqueues before closing connections
Commit: 7f796bb3b440d7f1b14c0e3b520462eb34f553af
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7f796bb3b440d7f1b14c0e3b520462eb34f553af
Commit description:
tipc_topsrv_stop() closed subscriber connections while the topology
server's send and receive workqueues were still running. Socket
callbacks and subscription events could then queue more work, and
in-flight send/recv work could drop the last connection reference
during the conn_idr walk.
That race produced several teardown failures: refcount_t addition on
0 from conn_get() on a connection whose release was blocked on
idr_lock, a subsequent use-after-free in tipc_conn_close(),
queue_work() on an already destroyed workqueue from the listener
data-ready callback, and an RCU stall in tipc_topsrv_exit_net()
while the walk spun under idr_lock.
Clear srv->listener under idr_lock so it acts as a shutdown flag,
skip queue_work() once it is NULL, destroy the workqueues to flush
in-flight work, and only then close the remaining connections.
Refuse tipc_conn_lookup() after that flag is cleared, and drop
idr_lock when the teardown walk finds no connection, so an
in-flight subscription event cannot pin idr_in_use while the
walk holds the lock.
v3 supersedes the narrower in-thread diff Tung Quang Nguyen
posted on 2026-09-23. It keeps his teardown order and adds the
lookup refusal and the empty-idr unlock.
Fixes: c5fa7b3 ("tipc: introduce new TIPC server infrastructure")
Cc: [email protected]
Reported-by: Vega <[email protected]>
Assisted-by: LLM
Signed-off-by: Yuqi Xu <[email protected]>
Reviewed-by: Ren Wei <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/tipc/topsrv.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=7f796bb3b440d7f1b14c0e3b520462eb34f553af
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99054 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99054
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: 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: IMPORTANT
KPANIC detected for this report: NO
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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