* [CVE-2026-89569][IMPORTANT] Bluetooth: RFCOMM: serialize security confirmation handling
@ 2026-09-12 1:10 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-12 1:10 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89569
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: Bluetooth: RFCOMM: serialize security confirmation handling
Commit: 1b7841ffad08e911e8c4b9470f3fa08423568940
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1b7841ffad08e911e8c4b9470f3fa08423568940
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89569
Analysis date: Fri, 11 Sep 2026 21:10:15 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89569 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89569
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-2026-89569 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-89569 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A use-after-free race exists in Bluetooth/RFCOMM security confirmation handling because rfcomm_security_cfm() looks up an RFCOMM session and walks its DLC list without holding rfcomm_mutex while the RFCOMM teardown path can concurrently unlink DLC objects and free the same session. A nearby Bluetooth peer may be able to influence the connection security confirmation and teardown timing so the callback reads a freed session list head or updates flags and timers in freed DLC objects, leading to kernel memory corruption or a crash. For the CVSS the PR:N is used because the attacker does not need local privileges on the target host and only needs Bluetooth adjacency to the exposed RFCOMM path. AV:A is used because exploitation requires proximity to the Bluetooth radio rather than normal Internet reachability. AC:H is used because reliable triggering depends on a race window between hci_rx_work and krfcommd session teardown. Impact is at least denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact due to use-after-free of kernel objects. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) SKIP CVE-2026-89569 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE REMOTE READ DANGER UAF NETWORK KPANIC MEMORY - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 5
* Conservative score: 5. No floor or cap changed the score.
* Raw paranoid score: 6
* Paranoid score: 6. No floor or cap changed the score.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +2 Real UAF / active lifetime violation. KASAN reports slab-use-after-free in rfcomm_security_cfm(), and the commit describes session and DLC objects being freed by krfcommd while hci_rx_work continues to use them.
* +1 Reliable kernel crash / strong DoS. The demonstrated stale access is in kernel Bluetooth workqueue context and can plausibly crash the host.
* +2 Adjacent network reachable trigger. The vulnerable path is reached from Bluetooth RFCOMM / HCI security confirmation handling, and the attacker model does not require local code execution or host-admin privilege when an RFCOMM Bluetooth path is exposed.
Paranoid additional signal:
* +1 Structured stale-object exploitation leverage. The stale objects are active RFCOMM session and DLC structures, and the callback may not only read the freed session list head but also update DLC flags or timers after teardown. This is more meaningful than an immediate NULL dereference, although controlled reclaim is not demonstrated.
Important non-awarded signals:
* Controlled reclaim is not demonstrated.
* Arbitrary kernel read/write is not demonstrated.
* Callback or function-pointer control is not demonstrated.
* Confidentiality and integrity are not scored as established consequences in ActionableScore merely because paranoid CVSS may use C:H/I:H.
* Extra Availability is not awarded because the same crash/DoS is already counted once.
* Weak LPE is not separately awarded because the unresolved exploitation concern is represented by the structured stale-object signal.
* Concrete repeated release/refcount was not awarded. The patch shows concurrent free and later stale access, but not a second put/release/refcount mutation on the same dangling reference.
Repeated release/refcount checklist:
* First release can end lifetime: yes, rfcomm_session_del() reaches kfree(s), and DLC unlink/free is part of teardown.
* Exact same reference survives: yes for the stale session pointer used by rfcomm_security_cfm().
* Second operation mutates lifetime/refcount: no concrete second lifetime/refcount mutation is shown.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage awarded: no.
* FLOOR 5 applied: not needed. Conservative arithmetic already reaches 5.
3. Reachability analysis
The plausible attacker is a nearby Bluetooth peer interacting with an exposed RFCOMM path. The trigger is not Internet-routable network traffic, so AV-like reachability is adjacent rather than full remote network. No host-admin-equivalent privilege is shown as required for the attacker side. The complete path depends on Bluetooth being enabled, RFCOMM being available, and connection security confirmation racing with RFCOMM session teardown.
HostAdminRequired is set to NO because the supplied evidence supports a below-host-admin external Bluetooth peer model rather than a local privileged management operation. NamespaceScopedPrivilege is NO because the issue is not based on namespace-scoped capabilities. Prior setup may exist in practice, such as Bluetooth being enabled and a profile using RFCOMM being reachable, but that is deployment exposure rather than host-admin privilege required by the attacker.
The race is real, but no separate timing penalty is applied. The evidence shows a concurrent hci_rx_work versus krfcommd teardown race, but Bluetooth connection/session operations can plausibly be retried. The race increases exploit difficulty but does not justify automatically downgrading the established UAF primitive.
4. Primitive and severity interpretation
The exact primitive is a real use-after-free race in Bluetooth RFCOMM security confirmation handling. rfcomm_security_cfm() obtains an RFCOMM session and traverses its DLC list without holding rfcomm_mutex, while krfcommd can concurrently close the session, unlink DLC objects, delete the session, and free it. The stale use is on active structured kernel objects, not fixed stale storage.
The demonstrated consequence is a KASAN slab-use-after-free and likely kernel crash/DoS. The stronger unresolved concern is that the stale path may touch freed DLC objects and update flags or timers, giving more exploitation relevance than a crash-only stale read. However, the patch and supplied context do not establish controlled reclaim, attacker-shaped replacement contents, arbitrary read/write, callback hijack, or demonstrated privilege escalation.
PrimitiveClass is CLASS_B because this is a real active-object kernel lifetime violation with unresolved exploitation leverage, but not a directly established CLASS_A primitive. ImportantCandidate is YES because the bug is adjacent-reachable, involves active structured objects, and includes possible stale updates to freed DLC state. AutoDowngradeAllowed is NO because automatic closure would discard a concrete UAF with meaningful unresolved exploitation leverage in a remotely adjacent Bluetooth protocol path.
Likely operational severity is Actionable Moderate at minimum, with Strong Important review justified if product exposure includes enabled Bluetooth RFCOMM services or profiles reachable by untrusted nearby devices.
5. One-sentence report phrase
A Bluetooth RFCOMM use-after-free race allows a nearby peer to influence security confirmation and teardown timing so rfcomm_security_cfm() may access freed session or DLC objects, causing at least a kernel crash and requiring manual review for possible post-free object corruption leverage.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: confirmed KASAN UAF in an adjacent-reachable Bluetooth RFCOMM path, with stale access to active session/DLC objects and possible updates to freed flags or timers.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: Bluetooth: RFCOMM: serialize security confirmation handling
Commit: 1b7841ffad08e911e8c4b9470f3fa08423568940
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1b7841ffad08e911e8c4b9470f3fa08423568940
Commit description:
rfcomm_security_cfm() looks up a session on session_list and then walks
its DLC list without holding rfcomm_mutex. Since RFCOMM session teardown
uses rfcomm_mutex, krfcommd can close and free the same session and DLCs
concurrently:
hci_rx_work krfcommd
----------- ---------
rfcomm_session_get()
rfcomm_lock()
rfcomm_session_close()
rfcomm_dlc_unlink()
rfcomm_session_del()
kfree(s)
rfcomm_unlock()
walk s->dlcs
The callback can then read a freed session list head and touch freed DLCs
while updating their flags or timers.
Serialize the session lookup and DLC traversal in rfcomm_security_cfm()
with rfcomm_mutex. This matches the existing RFCOMM session lifetime
rules and prevents concurrent rfcomm_session_del() / rfcomm_dlc_unlink()
from tearing the objects down while the callback is using them.
KASAN reported:
BUG: KASAN: slab-use-after-free in rfcomm_security_cfm+0x41c/0x440
Read of size 8 at addr ffff888111fb3960 by task kworker/u17:1/89
Workqueue: hci0 hci_rx_work
Call Trace:
rfcomm_security_cfm+0x41c/0x440
hci_encrypt_cfm+0x139/0x590
hci_encrypt_change_evt+0x37b/0xc40
hci_event_packet+0x71b/0xb20
hci_rx_work+0x293/0x730
Allocated by task 69:
rfcomm_session_add+0x9e/0x2f0
rfcomm_run+0x44b/0x41e0
Freed by task 69:
kfree+0x131/0x3c0
rfcomm_session_del+0x188/0x220
rfcomm_run+0x1985/0x41e0
Fixes: 08c30ac ("Bluetooth: Remove RFCOMM session refcnt")
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/rfcomm/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=1b7841ffad08e911e8c4b9470f3fa08423568940
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89569 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89569
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:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 7.5
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: 5
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: YES
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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