* [CVE-2026-89774][MODERATE 7.0] Bluetooth: SCO: hold sk properly in sco_conn_ready
@ 2026-09-16 9:13 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-16 9:13 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89774
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: SCO: hold sk properly in sco_conn_ready
Commit: 50aae396dc30377bec8e3b181b8346f8fd38f7d8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=50aae396dc30377bec8e3b181b8346f8fd38f7d8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89774
Analysis date: Wed, 16 Sep 2026 05:13:21 -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-2026-89774 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89774
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-89774 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89774 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/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: '7.1';DESCR 'Bluetooth SCO has a race in sco_conn_ready() where conn sk and the listening parent socket could be dereferenced without holding a stable reference. A concurrent sco_sock_release() can clear the connection socket and free the struct sock while sco_conn_ready() continues to use it, creating a use-after-free. For the CVSS the PR:L is used for the paranoid score because reliable triggering generally requires a local low privileged process that can create and close SCO sockets, while a Bluetooth adjacent peer may influence the connection ready timing. The issue is not reachable from the Internet and is limited to systems with Bluetooth SCO support and an exposed Bluetooth attack surface. Impact is at least denial of service via kernel crash and in worst case may allow confidentiality or integrity impact because the bug class is a real UAF on a kernel socket object.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) YES REMOTE LOCK DANGER INIT UAF NETWORK TIMER KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH NO NO 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
* Raw paranoid score: 6
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
No floor or cap changed the score.
2. Signal breakdown
Conservative positive signals:
* +2 Real UAF / active lifetime violation: the commit directly describes UAF on sk deref in sco_conn_ready when sco_sock_release clears conn->sk and sco_sock_kill may free the socket while sco_conn_ready still uses the stale struct sock.
* +1 Reliable kernel crash / strong DoS: stale struct sock dereference, lock_sock on a freed socket, state updates, timer cleanup, or callback invocation can plausibly fault or crash the kernel.
* +1 Local below-host-admin reachability: the evaluated path is Bluetooth SCO socket lifecycle handling. The supplied context supports PR:L rather than host-admin-only triggering because a local low privileged process can create and close SCO sockets while connection readiness occurs.
* +1 Attacker-influenced active-object lifetime manipulation: the local attacker can influence socket creation and close timing, and that lifetime transition is the root cause of the stale conn->sk and parent socket use.
Paranoid additional signal:
* +1 Structured stale-object exploitation leverage: the stale object is an active struct sock and the stale path may consume or modify meaningful fields, including socket state and sk_state_change callback flow. This is stronger than a shallow stale cleanup dereference, but still does not establish controlled reclaim or arbitrary write.
Non-awarded material signals:
* +2 Strong LPE / strong exploitation leverage not awarded: controlled reclaim, attacker-shaped replacement object, arbitrary kernel read/write, credential corruption, or callback control is not demonstrated.
* Concrete repeated release/refcount +1 not awarded: the patch adds sock_hold and sock_put, but the shown bug is stale dereference/use without proving a first put can free the exact object followed by a second lifetime-mutating put on the same dangling reference.
* Extra Availability +1 not awarded: the same kernel crash/DoS is already counted once.
* Confidentiality and Integrity impact not awarded as established consequences: C/I are plausible only in the paranoid sense because this is a real UAF on struct sock, not because the patch demonstrates disclosure or unauthorized modification.
* Race/timing penalty not applied: the bug is a race, but the local socket lifecycle can be attempted repeatedly and the prompt rules say not to subtract solely because a race exists.
* Remote network reachability +2 not awarded: this is Bluetooth-adjacent/local socket behavior, not Internet-reachable packet processing.
Repeated release/refcount checklist:
* First release can end lifetime: not established as the scored primitive.
* Exact same reference survives to a second lifetime mutation: not established.
* Second operation is a concrete lifetime/refcount mutation: not established.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage awarded: no.
* FLOOR 5 applied: no. Score reaches 5 by arithmetic.
3. Reachability analysis
The most plausible attacker model is a local below-host-admin user or process that can create, listen/connect, and close Bluetooth SCO sockets while a SCO connection transitions to ready state. A Bluetooth adjacent peer may influence connection timing, but the complete trigger is not a normal remote Internet network vector.
Host-admin-equivalent privilege is not positively established. Therefore HostAdminRequired=NO is used based on the supplied PR:L hint and normal Bluetooth socket semantics. NamespaceScopedPrivilege=NO because Bluetooth SCO is not shown as a fully namespace-scoped capability path, and no netns-only trigger chain is established.
Prior setup may require Bluetooth support, SCO support, and an available Bluetooth controller or emulated/test Bluetooth environment. This is a real deployment prerequisite, but not enough to classify it as rare physical-only hardware for scoring. The race is timing-dependent, but the create/close lifecycle can be retried, so no hard-race penalty is applied.
4. Primitive and severity interpretation
The exact primitive is a real use-after-free / stale lifetime use of struct sock in net/bluetooth/sco.c. It affects conn->sk in sco_conn_ready and similarly the listening parent socket returned by sco_get_sock_listen before the patch added refcount protection.
This is an active structured object UAF, not fixed stale storage. The stale use is also not purely cleanup/destructor-only: sco_conn_ready may lock the socket, clear timers, set sk_state, and call sk_state_change. Those operations consume meaningful socket structure state and leave unresolved exploitation leverage beyond a trivial NULL dereference or WARN.
PrimitiveClass=CLASS_B because a real kernel lifetime corruption primitive exists, but Class A is not established. The demonstrated consequence is kernel crash/DoS. The speculative consequence is stronger exploitation through reclaimed or corrupted struct sock state, but controlled replacement, callback hijack, arbitrary R/W, or LPE is not demonstrated.
ImportantCandidate=YES because this is an active-object UAF in Bluetooth socket handling with meaningful unresolved exploitation analysis. ManualReview=REQUIRED for the same reason. AutoDowngradeAllowed=NO because automatically closing it as ordinary Moderate would lose a concrete kernel lifetime primitive with unresolved post-free structured-object leverage.
Operationally, this is best treated as Actionable Moderate at minimum, with Strong Important candidacy requiring manual review.
5. One-sentence report phrase
Bluetooth SCO has a race in sco_conn_ready where conn sk or the listening parent socket can be used after concurrent socket close, causing a kernel UAF with likely DoS and unresolved exploitation leverage on struct sock state.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: this is a patch-confirmed race-based UAF on an active struct sock object, with local below-host-admin reachability and meaningful stale structured-object use beyond a simple crash-only cleanup path.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: Bluetooth: SCO: hold sk properly in sco_conn_ready
Commit: 50aae396dc30377bec8e3b181b8346f8fd38f7d8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=50aae396dc30377bec8e3b181b8346f8fd38f7d8
Commit description:
sk deref in sco_conn_ready must be done either under conn->lock, or
holding a refcount, to avoid concurrent close. conn->sk and parent sk is
currently accessed without either, and without checking parent->sk_state:
[Task 1] [Task 2]
sco_sock_release
sco_conn_ready
sk = conn->sk
lock_sock(sk)
conn->sk = NULL
lock_sock(sk)
release_sock(sk)
sco_sock_kill(sk)
UAF on sk deref
and similarly for access to sco_get_sock_listen() return value.
Fix possible UAF by holding sk refcount in sco_conn_ready() and making
sco_get_sock_listen() increase refcount. Also recheck after lock_sock
that the socket is still valid. Adjust conn->sk locking so it's
protected also by lock_sock() of the associated socket if any.
Fixes: 27c24fd ("Bluetooth: switch to lock_sock in SCO")
Signed-off-by: Pauli Virtanen <[email protected]>
Signed-off-by: Luiz Augusto von Dentz <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/bluetooth/sco.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=50aae396dc30377bec8e3b181b8346f8fd38f7d8
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89774 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89774
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:A/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 7.1
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: 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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