[CVE-2026-72333][MODERATE REGULAR] Bluetooth: L2CAP: fix tx ident leak for commands without a response

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-72333
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: L2CAP: fix tx ident leak for commands without a response
Commit: b8a32a5fc915b024c60f18d51b6cffd2bd64d4a6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b8a32a5fc915b024c60f18d51b6cffd2bd64d4a6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72333
Analysis date: Sat, 15 Aug 2026 06:20:54 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A Bluetooth peer can exhaust L2CAP TX signaling identifiers by causing repeated response-less `L2CAP_LE_CREDITS` commands, making later credits use invalid ident 0 and permanently stalling the affected LE CoC channel.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72333 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72333

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 REGULAR
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-2026-72333	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';*CWE-772;**CWE-400;CWE-404;BEST CVSS score: '4.3';DESCR 'A transmit ident leak in Bluetooth L2CAP can happen because L2CAP_LE_CREDITS commands allocate signaling identifiers but do not have a response that would release them later. A Bluetooth peer that streams data to the host can make the host send repeated credit packets until the 1-255 ident range is exhausted, after which credits may be sent with invalid ident 0 and dropped by validating remote stacks. This can permanently stall the affected LE CoC channel and cause denial of service for that Bluetooth data path. For the CVSS the PR:N is used because the attacker does not need local privileges on the target and only needs adjacent Bluetooth reachability to a usable L2CAP LE CoC path. The issue is not Internet reachable and practical exposure depends on Bluetooth pairing, service authorization, and whether untrusted peers can open or keep such channels.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4)  SKIP CVE-2026-72333 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 6c3ea155e5ee3e56606233acde8309afda66d483 YES  NO NO unknown 	MAYBE	REMOTE INIT LEAK NETWORK PACKET  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**

## 2. Signal breakdown

Conservative signals:

* `+2 Remote reachable / network-triggerable`: the trigger is an adjacent Bluetooth peer, not local code execution on the victim.
* `+1 Reliable DoS / resource exhaustion`: repeated `L2CAP_LE_CREDITS` packets can exhaust the 1-255 TX ident range after about 254 credit packets.
* `+1 Availability impact realistic`: the affected LE CoC channel can stall permanently because later credits are sent with invalid ident 0 and may be dropped.
* `-1 Rare or limited exposure condition`: exploitation requires Bluetooth reachability plus a usable LE CoC channel, and practical exposure may depend on pairing and service authorization.

Paranoid difference:

* The score becomes 4 if Bluetooth LE CoC exposure is considered reachable by an untrusted adjacent peer in the evaluated product and the exposure limitation penalty is not applied.

No memory corruption signals apply:

* No UAF, double free, OOB write, type confusion, arbitrary write, or reclaim primitive is shown.
* This is a protocol identifier leak / resource exhaustion issue, not an LPE-class memory safety bug.

## 3. Reachability analysis

A Bluetooth peer can trigger the issue by streaming data to the host over an LE CoC channel, causing the host to repeatedly send `L2CAP_LE_CREDITS`. No local account on the target is required, so the practical attacker position is adjacent Bluetooth reachability, not local privilege. Namespaces and containers are not relevant to triggering. The path is only exposed when Bluetooth and the relevant L2CAP LE CoC usage are enabled, and real deployments may require pairing, authorization, or a trusted peer relationship.

## 4. Severity interpretation

This behaves like an ordinary-to-borderline Moderate issue, not an Important-class vulnerability. The realistic impact is denial of service for the affected Bluetooth data channel. There is no evidence of kernel memory corruption, privilege escalation, confidentiality impact, or integrity impact. The issue deserves manual review mainly because it is externally triggerable over Bluetooth, but it should not be treated as a strong Important candidate without additional evidence.

## 5. One-sentence report phrase

A Bluetooth peer can exhaust L2CAP TX signaling identifiers by causing repeated response-less `L2CAP_LE_CREDITS` commands, making later credits use invalid ident 0 and permanently stalling the affected LE CoC channel.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the bug is adjacent-network reachable over Bluetooth, but the expected impact is limited to a scoped channel DoS with no supported memory corruption or privilege escalation primitive.

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: Bluetooth: L2CAP: fix tx ident leak for commands without a response
Commit: b8a32a5fc915b024c60f18d51b6cffd2bd64d4a6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b8a32a5fc915b024c60f18d51b6cffd2bd64d4a6

Commit description:

Commit 6c3ea15 ("Bluetooth: L2CAP: Fix not tracking outstanding
TX ident") changed ident allocation to use an IDA, releasing idents in
l2cap_put_ident() when the matching response command is received.

But identifiers allocated for commands that have no response defined
are never released. In particular L2CAP_LE_CREDITS is sent repeatedly for
the lifetime of an LE CoC channel, so a peer streaming data to the
host exhausts the 1-255 ident range after 254 credit packets. From
then on l2cap_get_ident() fails:

    kernel: Bluetooth: Unable to allocate ident: -28

and every subsequent L2CAP_LE_CREDITS packet is sent with ident 0,
which is invalid (Core Spec, Vol 3, Part A, Section 4: "Signaling
identifier 0x00 is an invalid identifier and shall never be used in
any command"). Remote stacks that validate the ident drop these
commands, never receive new credits, and the channel stalls
permanently. With default socket buffers this happens after roughly 0.5 MB
of received data (the exact amount depends on the socket receive buffer):

  < ACL Data TX: Handle 2048 flags 0x00 dlen 12
        LE L2CAP: LE Flow Control Credit (0x16) ident 0 len 4
          Source CID: 64
          Credits: 1

Release the ident immediately after sending L2CAP_LE_CREDITS since no
response will ever release it. Use a local variable instead of
chan->ident so that an ident that an EXT_FLOWCTL channel may be waiting on
(e.g. a pending reconfigure) is not overwritten by a credit packet.

Also add the missing L2CAP_LE_CONN_RSP case to l2cap_put_ident() so
idents allocated for outgoing L2CAP_LE_CONN_REQ commands are released
when the response arrives.

Fixes: 6c3ea15 ("Bluetooth: L2CAP: Fix not tracking outstanding TX ident")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=221629
Assisted-by: Claude:claude-opus-4.8
Assisted-by: Fable:5
Signed-off-by: Stig Hornang <stig@hornang.me>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/bluetooth/l2cap_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=b8a32a5fc915b024c60f18d51b6cffd2bd64d4a6

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DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-72333 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72333

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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 4.3

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: 3
  Paranoid ActionableScore: 4

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).