From: AL-KERNEL <[email protected]>
To: [email protected]
Subject: [CVE-2026-99228][LOW] io_uring/io-wq: don't lose the signal that ends work
Date: Mon, 02 Nov 2026 22:14:59 -0400 [thread overview]
Message-ID: <[email protected]> (raw)
CVE: CVE-2026-99228
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: io_uring/io-wq: don't lose the signal that ends work
Commit: ddccc60f036b309430cf130d48aafed94ef7355a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ddccc60f036b309430cf130d48aafed94ef7355a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99228
Analysis date: Mon, 02 Nov 2026 22:14:59 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A local unprivileged io_uring user can reliably cause its exiting process to hang by racing io-wq shutdown with a blocking asynchronous FIFO open.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99228 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99228
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: LOW
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-2026-99228 LOW https://www.kernelcve.org/list/?q=CVE-2026-99228 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=2 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both LOW) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;*CWE-833;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A signal handling race in io-wq can lose the one time TIF_NOTIFY_SIGNAL wakeup used during worker shutdown. A worker may clear the flag while running task work and then start bounded IORING_OP_OPENAT work on a FIFO without a partner, causing fifo_open to wait and preventing io-wq teardown and the submitting thread from completing exit. For the CVSS the PR:L value is selected because an attacker must execute a local process and submit a crafted io_uring request, while no administrative capability is normally required. The issue is not directly network reachable and no UAF, OOB access, information leak, or write primitive is shown. Base impact is limited availability loss for the affected process. The paranoid availability value accounts for possible repeated accumulation of stuck workers, but host wide exhaustion is not established. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to LOW because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE INIT LEAK HARDWARE TEST IO_URING INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 2.
* Paranoid score: 2; repeated host-wide exhaustion is not established.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Local unprivileged trigger: an ordinary process can submit an asynchronous `IORING_OP_OPENAT` against a FIFO and then exit; no administrative capability is indicated.
* +1 Availability impact: the lost shutdown signal can leave the submitting thread stuck in `do_exit()` until the process is killed.
* No kernel crash point: the demonstrated effect is a process/io-wq teardown hang, not panic or host-wide fatal failure.
* No corruption point: the patch shows a signal-state race, not UAF, OOB access, stale-object use, or a kernel write primitive.
* No extra availability point: accumulation of stuck workers or host-wide exhaustion is unproven.
* No race penalty: the failure reportedly occurs in more than nine of ten attempts, so timing is not shown to be difficult or unreliable.
* NEW52/B5-R does not apply: there is no heap OOB write, retry-accumulated offset, or later consumption of corrupted structured state.
* NEW53/B3-PENDING and NEW54/B4-PENDING do not apply: no shared-backing write or authorization DENY-to-ALLOW transition exists.
3. Reachability analysis
The complete demonstrated trigger is available to a normal local process through io_uring and FIFO operations. It requires neither host UID 0 nor a capability or namespace-scoped privilege. No prior privileged setup, special hardware, boot option, or unusual subsystem configuration is shown. The ordering is a race, but it is highly reproducible in the supplied test.
4. Primitive and severity reading
The defect loses the one-time `TIF_NOTIFY_SIGNAL` wakeup between worker shutdown and bounded-work execution. The worker can consequently block in `fifo_open()`, preventing io-wq teardown and completion of process exit. This is synchronization-related process availability loss, not memory corruption or an authorization bypass. Host-wide resource exhaustion remains theoretical, so there is no Important-preserving primitive and automatic downgrade is allowed.
5. One-sentence report phrase
A local unprivileged io_uring user can reliably cause its exiting process to hang by racing io-wq shutdown with a blocking asynchronous FIFO open.
6. Manual review advice
NO MANUAL CHECK NEEDED
The patch-supported impact is limited to a killable process teardown hang without kernel corruption, host crash, or security-boundary bypass.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: io_uring/io-wq: don't lose the signal that ends work
Commit: ddccc60f036b309430cf130d48aafed94ef7355a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ddccc60f036b309430cf130d48aafed94ef7355a
Commit description:
When a thread exits, only its tracked requests are cancelled. Then its
io-wq is torn down. io_wq_exit_workers() signals every worker, to get it
out of an interruptible sleep, and waits for all of them to exit. Before
they do, they go through the work that is left. Unbounded work is
cancelled. Bounded work is run, as it is expected to end by itself.
Not all of it does. An open has no file yet, so it counts as bounded, and
the open of a FIFO waits for the other end. That is what the signal is for.
But the workers are signalled once, and a worker that hasn't started the
work by then loses the signal:
io_wq_exit_workers() io_worker_handle_work()
io_wq_worker_wake()
set TIF_NOTIFY_SIGNAL
io_assign_current_work()
io_run_task_work()
clear TIF_NOTIFY_SIGNAL
io_wq_submit_work()
fifo_open()
wait_for_partner()
wait_for_completion_timeout()
The thread never gets out of do_exit():
IORING_OP_OPENAT of a FIFO without a writer, IOSQE_ASYNC
exit of the thread that has submitted it
hangs in more than 9 of 10 attempts (4 CPUs, KVM), until the process is
killed.
Set TIF_NOTIFY_SIGNAL for bounded work that is started with IO_WQ_BIT_EXIT
set. The bit is set before the workers are signalled, and it is tested
after the flag has been cleared, with clear_notify_signal() providing the
barrier. So either the flag stays, or the bit is seen.
Work that is started while the io-wq exits is treated like work that is
being run at that time: it isn't interrupted unless it waits
interruptibly.
[ 6.1: work->flags is not atomic here ]
Fixes: afcc401 ("io-wq: provide an io_wq_put_and_exit() helper")
Assisted-by: LLM
Signed-off-by: Josef Bacik <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jens Axboe <[email protected]>
Co-Authored-By: Claude Fable 5.1 <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
io_uring/io-wq.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=ddccc60f036b309430cf130d48aafed94ef7355a
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99228 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99228
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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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: unknown
Paranoid ActionableScore: 2
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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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