* [CVE-2026-99231][IMPORTANT] io_uring/waitid: own the request before clearing ->head
@ 2026-11-03 3:04 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-11-03 3:04 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99231
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: io_uring/waitid: own the request before clearing ->head
Commit: bf01da1a9cca4a54e5c30b8344e52c26afb87be7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bf01da1a9cca4a54e5c30b8344e52c26afb87be7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99231
Analysis date: Mon, 02 Nov 2026 23:04:32 -0400
ActionableScore: 6
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A local io_uring race permits a freed waitid request to be reused before a stale refcount update and task-work decision, causing active-object corruption and a demonstrated slab UAF.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99231 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99231
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-2026-99231 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-99231 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 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-416;CWE-362;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 io_uring waitid clears iw head before the wake handler owns the request. A concurrent completion or cancellation can then skip wait queue locking, free and reuse the request, while the handler still increments refs in the reused per opcode storage and may queue work for the wrong object. The demonstrated result is a slab use after free after request reuse, and the stale atomic update provides a limited memory corruption primitive with a plausible kernel crash or privilege escalation path. For the CVSS the PR:L value is selected because an unprivileged local process must execute io_uring operations and arrange the waitid race. AC:H reflects the timing dependent ownership window. The issue is not directly network reachable. Automated impact decision path. The original SimpleNet classifier selected LOW. 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 LOW to MODERATE_KPANIC because the ActionableScore threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to IMPORTANT because the ActionableScore threshold rule was applied. KP and FD specialist checks stage IMPORTANT to IMPORTANT because a specific evidence based protection or manual review veto was applied. final reconciliation stage IMPORTANT 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 INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 and INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 and V59_LEGACY_CLASSA_KP_VETO and MANUAL_REVIEW_REQUIRED 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 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 LOCK LEAK UAF HARDWARE IO_URING INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 V59_LEGACY_CLASSA_KP_VETO MANUAL_REVIEW_REQUIRED TEMP_KPANIC_MERGE_IMPORTANT_WINS KPANIC_UNSUPPORTED_REMOVED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=6
PrimitiveClass=CLASS_A
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 6.
* Conservative score: 6; no floor or cap applied.
* Raw paranoid score: 6.
* Paranoid score: 6; stronger effects would require unsupported arbitrary-write, disclosure, or LPE assumptions.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 real UAF/lifetime violation: `->head` is cleared before ownership is acquired, allowing completion to free and reuse the request while the wake handler still accesses it.
* +2 strong corruption leverage: `atomic_fetch_inc(&iw->refs)` writes into reused per-opcode storage, and a zero result can queue `io_waitid_cb()` for the wrong request. This is attacker-influenced active-object corruption, not merely a stale read.
* +1 local unprivileged trigger: the supplied evidence grounds the complete trigger in ordinary local io_uring operations.
* +1 attacker-influenced lifetime/reuse sequence: the actor can submit waitid operations and arrange request reuse as a waiting receive request.
* +1 reliable crash/DoS: the commit provides a KASAN slab-UAF trace in a later socket wakeup.
* -1 hard timing: exploiting the ownership window is race-dependent, and the demonstrated window was held open using an artificial delay.
* No extra availability point: it would duplicate the same crash.
* No C/I, arbitrary write, callback hijack, controlled target, or proven LPE points. The stale atomic update is limited and its ultimate target/effect is not arbitrary.
* This is not B5-R: no retry-accumulated heap OOB write is shown.
* No repeated release/refcount signal applies; this is stale access and mutation after concurrent request completion, not two puts on the same reference.
3. Reachability analysis
A normal local process can use io_uring waitid, create the relevant requests, and race wakeup against completion or cancellation. No host UID 0, capability, namespace privilege, prior privileged setup, special hardware, or remote input is shown as necessary. Repeated attempts appear possible, but success remains timing-sensitive.
4. Primitive and severity reading
The primitive is an active structured-request UAF with a write-like atomic increment into storage already reused for another opcode, potentially followed by task-work scheduling under the wrong object interpretation. The demonstrated downstream result is another slab UAF and kernel crash. Controlled arbitrary memory access, confidentiality impact, and privilege escalation remain unproven.
This is CLASS_A because concrete reuse plus corruption of the replacement request is shown. ImportantCandidate is YES and automatic downgrade is unsafe because exploit leverage of the wrong-object ref mutation and callback scheduling requires manual analysis.
5. One-sentence report phrase
A local io_uring race permits a freed waitid request to be reused before a stale refcount update and task-work decision, causing active-object corruption and a demonstrated slab UAF.
6. Manual review advice
MANUAL CHECK REQUIRED
Review replacement-request control, stale atomic-write placement, and whether wrong task-work scheduling can provide leverage beyond the demonstrated crash.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: io_uring/waitid: own the request before clearing ->head
Commit: bf01da1a9cca4a54e5c30b8344e52c26afb87be7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bf01da1a9cca4a54e5c30b8344e52c26afb87be7
Commit description:
io_waitid_remove_wq() only takes the wait queue lock if ->head is set.
io_waitid_wait() clears ->head first thing, before it tries to become the
owner of the request by bumping ->refs. If somebody else owns the request
at that point, nothing keeps it from completing the request while the
wake up handler is still going to touch it:
CPU0 (io_waitid_wait) CPU1 (io_waitid, holds a ref)
list_del_init(&wait->entry)
smp_store_release(&iw->head, NULL)
__do_wait() finds another child
io_waitid_remove_wq()
// ->head == NULL, no locking
io_waitid_finish(), IOU_COMPLETE
// request freed and reused
atomic_fetch_inc(&iw->refs)
The same goes for __io_waitid_cancel() if it claims the request in that
window. ->refs is part of the per opcode data of the request, so this
increments whatever the next user of the request keeps there. If that
happens to be zero, the handler concludes that it owns the request, and
queues io_waitid_cb() for it. With the window held open by a delay, and
the request reused for a receive that is waiting for data:
BUG: KASAN: slab-use-after-free in __wake_up_common+0x1ca/0x1f0
__wake_up_sync_key+0x36/0x50
sock_def_readable+0xf1/0x420
unix_stream_sendmsg+0x60b/0x1110
Allocated by task 87:
io_arm_apoll+0x1ed/0x940
Freed by task 87:
__io_submit_flush_completions+0x118d/0x1a10
tctx_task_work_run+0x327/0x950
Only clear ->head once the handler owns the request. If it doesn't, the
owner finds ->head set and has to wait for the lock, which is held by the
caller of the handler. Deleting the already deleted entry again is
harmless.
Fixes: ab673c1 ("io_uring/waitid: use io_waitid_remove_wq() consistently")
Assisted-by: LLM
Signed-off-by: Josef Bacik <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jens Axboe <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
io_uring/waitid.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=bf01da1a9cca4a54e5c30b8344e52c26afb87be7
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99231 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99231
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: unknown
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: 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).
^ permalink raw reply [relevance 21%]
Results 1-1 of 1 | reverse | sort options + mbox downloads above
-- links below jump to the message on this page --
2026-11-03 3:04 21% [CVE-2026-99231][IMPORTANT] io_uring/waitid: own the request before clearing ->head AL-KERNEL
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox