* [CVE-2026-99268][LOW] io_uring: wake ring pollers for local task_work
@ 2026-11-04 2:38 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-11-04 2:38 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99268
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: io_uring: wake ring pollers for local task_work
Commit: 9bb28e7740ce78beecafc5db074b45f4cbeb8a47
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9bb28e7740ce78beecafc5db074b45f4cbeb8a47
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99268
Analysis date: Tue, 03 Nov 2026 22:38:21 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A missed io_uring poll wake-up can indefinitely block an unprivileged application using deferred task running, without evidence of kernel corruption or host-wide denial of service.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99268 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99268
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-2026-99268 LOW https://www.kernelcve.org/list/?q=CVE-2026-99268 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:L';CWE-662;CWE-667;BEST CVSS score: '3.3';DESCR 'A synchronization logic bug in io_uring can leave an application sleeping indefinitely when a ring uses IORING_SETUP_DEFER_TASKRUN and the application waits through poll or epoll. Local task_work may become pending after io_uring_poll has put the submitter to sleep, while poll_wq is not notified until CQEs are committed by that same submitter. For the CVSS the PR:L value is used because a local user process must create and operate the affected io_uring instance. The demonstrated impact is limited availability loss for the affected application with no supported memory corruption, confidentiality loss, integrity loss, kernel crash, or direct network trigger. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 3.3 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. 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. 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 LEAK IO_URING - - 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; no stronger technically supported effect exists.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Local unprivileged trigger: an ordinary process can create and operate its own `IORING_SETUP_DEFER_TASKRUN` ring and wait through poll/epoll.
* +1 Limited availability impact: a missed `poll_wq` wake can leave the affected application sleeping indefinitely despite pending local work.
* No memory-corruption, UAF, OOB access, authorization bypass, kernel crash, confidentiality impact, or integrity impact is shown.
* No extra strong-DoS point: the demonstrated failure is confined to the waiting application, not a host-wide kernel failure.
* NEW52/B5-R does not apply: there is no retry-accumulated index or heap OOB write.
* NEW53/B3-PENDING does not apply: no shared-backing write occurs.
* NEW54/B4-PENDING does not apply: no mandatory authorization decision changes from DENY to ALLOW.
3. Reachability analysis
The affected process itself creates the io_uring instance, enables deferred task running, and sleeps through poll/epoll. This is a normal local unprivileged interface; no host UID 0, capability, namespace privilege, prior privileged setup, special hardware, boot option, or race timing is evidenced as necessary.
4. Primitive and severity reading
The defect is a missed wake-up: local task work becomes pending after the poller sleeps, but `poll_wq` is not notified until CQEs are committed by the same sleeping submitter. The patch restores notification, using RCU only to avoid recursive wait-queue locking when invoked from a wake handler. This is synchronization/liveness behavior, not stale-object use or memory corruption. The shown effect is application-local unavailability; stronger host or security-boundary effects are unsupported.
5. One-sentence report phrase
A missed io_uring poll wake-up can indefinitely block an unprivileged application using deferred task running, without evidence of kernel corruption or host-wide denial of service.
6. Manual review advice
NO MANUAL CHECK NEEDED
The patch and call path establish a narrow application-liveness regression with no unresolved security primitive.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: io_uring: wake ring pollers for local task_work
Commit: 9bb28e7740ce78beecafc5db074b45f4cbeb8a47
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9bb28e7740ce78beecafc5db074b45f4cbeb8a47
Commit description:
With IORING_SETUP_DEFER_TASKRUN completions are queued as local work, and
only become CQEs when the submitter enters the kernel to wait for events.
For an application that finds out via poll() or epoll on the ring fd when
it is time to do that, io_uring_poll() reports EPOLLIN if local work is
pending.
That only helps if the work is there at the time of the call. When
DEFER_TASKRUN was added, io_req_local_work_add() did io_cqring_wake(),
which took care of tasks sleeping in poll() as well. Then polling got a
wait queue of its own, ->poll_wq, and the wake up in
io_req_local_work_add() was replaced by waking the submitter directly.
Since then ->poll_wq is only woken when CQEs are committed, which for
such a ring is done by the very task that is waiting to be told to:
submitter completion
poll(ring_fd)
io_uring_poll() // nothing yet
schedule()
io_req_local_work_add()
// ->cq_wait_nr: nobody waits
// sleeps on
Wake ->poll_wq when the first entry is put on the work list. Like for the
eventfd, that must not be done right away if the work is queued from a
wake up handler, as the chain of wake ups could get back to the wait
queue whose lock is held. Use an RCU callback in that case, with a
reference to the ring.
[ 6.6: io_req_local_work_add() lives in io_uring/io_uring.c, and with no IOU_F_TWQ_IN_WAKE to tell a wake up handler context apart, the ->poll_wq wake up is always deferred to an RCU callback ]
Fixes: 130bd68 ("io_uring: waitqueue-less cq waiting")
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_uring.c
include/linux/io_uring_types.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=9bb28e7740ce78beecafc5db074b45f4cbeb8a47
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99268 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99268
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: Not available
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS score: 3.3
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: 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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