* [CVE-2026-98733][MODERATE 7.0] Bluetooth: hci_core: Serialize fragmented ISO packet queueing
@ 2026-10-19 8:29 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-19 8:29 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98733
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: hci_core: Serialize fragmented ISO packet queueing
Commit: d6d709981208567868c5c01ebd1bec5e5e7fdab0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d6d709981208567868c5c01ebd1bec5e5e7fdab0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98733
Analysis date: Mon, 19 Oct 2026 04:29:28 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A local fragmented Bluetooth ISO send can race with transmit dequeue and driver release, causing a write through a freed SKB tail pointer and active queue corruption with at least kernel crash impact and unresolved privilege escalation potential.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98733 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98733
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: MODERATE 7.0
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-2026-98733 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98733 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both 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 the Bluetooth HCI ISO fragmented transmit path allows hci_queue_iso to update the packet queue without holding its lock while the transmit worker can dequeue and release the previous tail SKB. If the driver frees that SKB before insertion resumes, __skb_queue_tail can write through the stale tail pointer and cause a slab use after free or corrupt the queue. A local process can reach the affected path through iso_sock_sendmsg when fragmented ISO packets are queued while transmission is active. For the CVSS the PR:L value is selected because local code execution and access to a Bluetooth ISO socket are required, while full administrative privileges are not clearly required by the affected send path. AC:H reflects the timing dependent race between packet insertion, dequeue, and driver release. The issue is not directly network reachable because a remote Bluetooth peer cannot by itself invoke the local sendmsg path based on the available evidence. Impact is at least a local denial of service through a kernel crash and may include confidentiality or integrity impact because the stale pointer is used for a write into freed slab memory. The paranoid score uses C:H I:H A:H because a confirmed write use after free can potentially support privilege escalation if object reuse and race timing become controllable, but that escalation path is not demonstrated. 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 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 has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP. The independent weaker Aegis shadow evaluated CVSS 4.7 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE REMOTE LOCK DANGER UAF NETWORK LINUS KPANIC PACKET DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP - - 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 conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap changed either score. The Real UAF floor of 4 is already met by the conservative arithmetic.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
## 2. Signal breakdown
Conservative signals:
* +2 Real UAF. The transmit worker can dequeue and release the old tail SKB before `__skb_queue_tail()` resumes and writes through that stale pointer.
* +1 Reliable kernel crash or strong DoS. KASAN confirms slab use-after-free, and concurrent queue updates can corrupt the active SKB queue.
* +1 Attacker-influenced active-object lifetime manipulation. Repeated fragmented ISO sends allocate and enqueue SKBs while the transmit worker drives dequeue and release of the same queue.
* Total: 4.
Additional paranoid signal:
* +1 Structured stale-object exploitation leverage. The stale operation is a write to the freed SKB tail linkage, not merely a read or immediate cleanup fault. The value written is a kernel SKB pointer, and the corrupted queue remains subject to scheduler and driver processing.
* Total: 5.
Not awarded:
* No controlled reclaim, arbitrary target selection, arbitrary write, callback control, disclosure, or demonstrated privilege escalation.
* No remote-reachability bonus. A remote Bluetooth peer is not shown to invoke the local `iso_sock_sendmsg()` operation independently.
* No race penalty. The race is timing-dependent, but fragmented sends and worker processing appear repeatable rather than a proven narrow one-shot event.
* No additional availability point because it would duplicate the same crash and queue-corruption consequence.
* No concrete repeated release or refcount signal. The bug performs a stale linkage write after the driver frees the SKB, not a second `put`, `free`, or refcount mutation.
* No B5-R retry-accumulated OOB signal, B3-PENDING shared-backing signal, or B4 authorization signal applies.
## 3. Reachability analysis
The demonstrated entry point is a local `sendto()` operation through `iso_sock_sendmsg()` using fragmented Bluetooth ISO traffic. The supplied evidence does not establish a remote-only trigger.
A local process controls fragmented packet submission and can plausibly repeat the queueing sequence while the transmit worker drains the queue. However, the complete privilege checks and setup requirements for creating and using the relevant ISO connection are not shown. Therefore, host-admin privilege is not positively established, but below-host-admin reachability is also not sufficiently proven for `HostAdminRequired=NO`.
No evidence establishes that the complete operation is available through attacker-created user or network namespaces. Bluetooth hardware, VHCI, or an equivalent ISO-capable setup is required, but the evidence does not support a rare-hardware penalty. Race repeatability appears plausible under sustained fragmented transmission.
## 4. Primitive and severity interpretation
The exact primitive is a write use-after-free against an active structured `sk_buff`. After the old queue tail is dequeued and freed, `__skb_queue_tail()` resumes and writes the new SKB pointer into the stale tail linkage. Concurrent operations may also leave the live queue internally corrupted.
This is broader active use, not cleanup or destructor-only access. It is not a repeated release or refcount case because the vulnerable operation modifies stale list linkage rather than releasing the same object again.
The issue is CLASS_B. The demonstrated consequence is kernel memory corruption with credible crash or DoS. A stronger consequence such as privilege escalation remains unresolved because controlled reclaim and attacker-directed target selection are not demonstrated.
`ImportantCandidate=YES` is justified by the concrete post-free write into an active queue object that is subsequently consumed by privileged scheduler and driver code. `AutoDowngradeAllowed=NO` is appropriate because automatically treating this as crash-only would discard meaningful unresolved exploitation leverage. This remains an Important review candidate rather than proof of Important severity.
## 5. One-sentence report phrase
A local fragmented Bluetooth ISO send can race with transmit dequeue and driver release, causing a write through a freed SKB tail pointer and active queue corruption with at least kernel crash impact and unresolved privilege escalation potential.
## 6. Manual review recommendation
MANUAL CHECK REQUIRED
The confirmed write use-after-free affects active SKB linkage and downstream queue processing, while reclaim control, exact ISO socket privileges, and exploitation beyond DoS remain unresolved.
## 7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: Bluetooth: hci_core: Serialize fragmented ISO packet queueing
Commit: d6d709981208567868c5c01ebd1bec5e5e7fdab0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d6d709981208567868c5c01ebd1bec5e5e7fdab0
Commit description:
The fragmented path in hci_queue_iso() calls __skb_queue_tail() without
holding conn->data_q.lock. The socket lock serializes senders, but the
transmit worker can concurrently remove packets from this queue using
skb_dequeue().
After an insertion saves the old tail pointer, hci_sched_iso() can dequeue
that packet and pass it to the driver. The driver can free the packet
before the insertion resumes and writes to the old tail's next pointer,
causing a use-after-free. Concurrent updates can also corrupt the queue.
KASAN reported:
BUG: KASAN: slab-use-after-free in hci_send_iso+0xc7d/0xe10
Call Trace:
hci_send_iso+0xc7d/0xe10
iso_sock_sendmsg+0x710/0x900
__sys_sendto+0x34a/0x3a0
Allocated by task 86:
__alloc_skb+0xdd/0x820
alloc_skb_with_frags+0x7e/0x770
sock_alloc_send_pskb+0x67a/0x820
bt_skb_sendmsg.constprop.0+0xc0/0x6c0
iso_sock_sendmsg+0x44e/0x900
Freed by task 90:
kmem_cache_free+0xcb/0x3d0
vhci_read+0x33f/0x4d0
vfs_read+0x177/0xa20
Hold the queue lock across the entire fragment batch, as hci_queue_acl()
does, to serialize insertion against dequeue while preserving fragment
ordering.
Fixes: 26afbd8 ("Bluetooth: Add initial implementation of CIS connections")
Cc: [email protected]
Signed-off-by: Chengfeng Ye <[email protected]>
Signed-off-by: Luiz Augusto von Dentz <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/bluetooth/hci_core.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=d6d709981208567868c5c01ebd1bec5e5e7fdab0
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98733 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98733
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: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0
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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