[CVE-2026-68188][MODERATE 7.0] Bluetooth: RFCOMM: Fix session UAF in set_termios

[CVE-2026-68188][MODERATE 7.0] Bluetooth: RFCOMM: Fix session UAF in set_termios

[AL-KERNEL]

CVE: CVE-2026-68188
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: RFCOMM: Fix session UAF in set_termios
Commit: 2894bd8c68e97accd758ca6e5fc375d7e9e8882c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2894bd8c68e97accd758ca6e5fc375d7e9e8882c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68188
Analysis date: Mon, 10 Aug 2026 11:44:22 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A local race in the Bluetooth RFCOMM TTY termios path can leave `rfcomm_tty_set_termios()` using a freed RFCOMM session pointer in `rfcomm_send_rpn()`, causing a confirmed kernel use-after-free and at least local DoS, with privilege-escalation potential requiring manual review.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-68188 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68188

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-2026-68188	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use-after-free exists in the Bluetooth RFCOMM TTY termios path because rfcomm_tty_set_termios reads dlc session without holding rfcomm_mutex and later passes that pointer to rfcomm_send_rpn. A concurrent krfcommd path can detach the DLC and free the RFCOMM session while the ioctl path still uses it, and KASAN reports a slab use-after-free when rfcomm_send_rpn reads session initiator and session sock. For the CVSS the PR:L is used for the paranoid score because a local user or process with access to the RFCOMM TTY device can drive the ioctl path, while a reduced capability service account or container style context should not automatically be treated as full administrator privilege. The issue is not directly reachable from the public network. A Bluetooth peer may help create the timing condition by closing or disrupting the session, but exploitation still depends on local RFCOMM TTY access and a race window. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality and integrity impact due to kernel use-after-free, so manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE READ DANGER RACE UAF NETWORK TEST KPANIC 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. The path is reachable through a local RFCOMM TTY ioctl / termios operation by a process that can access the RFCOMM TTY device.
* Memory corruption, weak primitive: +1. KASAN confirms a slab use-after-free in `rfcomm_send_rpn()`, but the patch shows a race stale pointer dereference, not attacker-controlled reclaim, overwrite, callback control, or type confusion.
* Real lifetime corruption: +1. `dlc->session` can be freed by `krfcommd` while the TTY path continues using the old pointer.
* Reliable kernel crash / strong DoS: +1. The reported KASAN trace shows a concrete UAF read in kernel context and a realistic crash path.
* Hard or unreliable race / special timing required: -1. Exploitation depends on a race between `rfcomm_tty_set_termios()` and RFCOMM session teardown.
* Availability impact realistic: +1. The demonstrated outcome is a kernel UAF that can crash the system.

Paranoid additional signal:

* Practical exploitability concern from confirmed UAF path: +1. The bug is not just theoretical because the commit provides a concrete race sequence and KASAN evidence from a PoC task, but the primitive remains weak and race dependent.

Not counted:

* Remote reachable / network-triggerable: +0. A Bluetooth peer may influence session teardown timing, but the vulnerable ioctl path is local.
* Strong LPE plausibility: +0. No attacker-controlled reclaim, overwrite, stale callback, refcount takeover, or type confusion is shown.
* Confidentiality / integrity impact: +0 for conservative score. Possible LPE remains a manual-review concern, not demonstrated by the patch.

## 3. Reachability analysis

The direct trigger is local access to an RFCOMM TTY device followed by termios changes that call `rfcomm_tty_set_termios()`. A concurrent RFCOMM teardown in `krfcommd` can clear `dlc->session` and free the session while the ioctl path still uses the pointer.

This is not a public network reachable vulnerability. Bluetooth interaction can help create the session lifecycle and may influence disconnect timing, but the vulnerable code path requires local RFCOMM TTY access. Namespace and container impact depends on whether the container or reduced-privilege service is given access to Bluetooth / RFCOMM TTY devices. Such access should be treated as PR:L rather than full host-root in practical triage.

RFCOMM is not a universal default-exposed path, but it is a real local kernel interface when Bluetooth RFCOMM TTY support is enabled and configured.

Call-site confidence: high. The patch includes the vulnerable caller, the new locking helper, and the dereference target path.

## 4. Severity interpretation

This behaves more like an actionable Moderate kernel UAF than an ordinary Moderate cleanup bug. The realistic demonstrated impact is local denial of service through a race-triggered kernel UAF and crash.

Theoretical privilege escalation cannot be ruled out because this is a real kernel use-after-free involving a session object and socket-related fields. However, the patch does not show attacker-controlled reclaim, write-after-free, callback dispatch, object replacement, or a clear arbitrary read/write primitive. Therefore it should not be promoted directly to Strong Important on the conservative evidence alone, but it should not be auto-closed.

## 5. One-sentence report phrase

A local race in the Bluetooth RFCOMM TTY termios path can leave `rfcomm_tty_set_termios()` using a freed RFCOMM session pointer in `rfcomm_send_rpn()`, causing a confirmed kernel use-after-free and at least local DoS, with privilege-escalation potential requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: confirmed kernel UAF plus race and local user-triggerable ioctl path. The currently visible primitive is weak and likely DoS-first, but kernel lifetime bugs of this class need manual review before closure.

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

Patch: Bluetooth: RFCOMM: Fix session UAF in set_termios
Commit: 2894bd8c68e97accd758ca6e5fc375d7e9e8882c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2894bd8c68e97accd758ca6e5fc375d7e9e8882c

Commit description:

rfcomm_tty_set_termios() tests dlc->session without rfcomm_mutex and
later passes the pointer to rfcomm_send_rpn(). The latter dereferences
both session->initiator and session->sock. Meanwhile, krfcommd can
unlink the DLC and free the session while holding rfcomm_mutex.

The race can proceed as follows:

  TTY ioctl task                 krfcommd
  --------------                 --------
  load dlc->session
  enter rfcomm_send_rpn()
                                 lock rfcomm_mutex
                                 clear dlc->session
                                 free session
                                 unlock rfcomm_mutex
  read session->initiator

KASAN reported:

  BUG: KASAN: slab-use-after-free in rfcomm_send_rpn+0x297/0x2a0
  Read of size 4 at addr ffff88810012a850 by task poc/92

  Call Trace:
   rfcomm_send_rpn+0x297/0x2a0
   rfcomm_tty_set_termios+0x50d/0x850
   tty_set_termios+0x596/0x950
   set_termios+0x46a/0x6e0
   tty_mode_ioctl+0x152/0xbd0
   tty_ioctl+0x915/0x1240
   __x64_sys_ioctl+0x134/0x1c0

  Allocated by task 92:
   rfcomm_session_add+0x9e/0x2e0
   rfcomm_dlc_open+0x8b1/0xe00
   rfcomm_dev_activate+0x85/0x1a0
   rfcomm_tty_open+0x90/0x280

  Freed by task 68:
   kfree+0x131/0x3c0
   rfcomm_session_del+0x119/0x180
   rfcomm_run+0x737/0x4710

Add rfcomm_dlc_send_rpn(), which holds rfcomm_mutex while it verifies
that the DLC is still attached and sends the RPN frame. Have the TTY
path use the helper and drop its unlocked session check. This keeps the
session valid through both the frame construction and socket send.

Fixes: 3a5e903 ("[Bluetooth]: Implement RFCOMM remote port negotiation")
Cc: stable@vger.kernel.org
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  include/net/bluetooth/rfcomm.h
  net/bluetooth/rfcomm/core.c
  net/bluetooth/rfcomm/tty.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=2894bd8c68e97accd758ca6e5fc375d7e9e8882c

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

The original Linux kernel CVE announcement for CVE-2026-68188 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68188

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