From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98455][MODERATE REGULAR] Bluetooth: RFCOMM: fix NULL dereference of dlc->session in RFCOMM_CONNINFO Date: Fri, 23 Oct 2026 20:17:52 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98455 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: c3aee3fc1287c8a555baf3895959087cb0c33fe8 List-Id: CVE: CVE-2026-98455 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: Bluetooth: RFCOMM: fix NULL dereference of dlc->session in RFCOMM_CONNINFO Commit: c3aee3fc1287c8a555baf3895959087cb0c33fe8 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c3aee3fc1287c8a555baf3895959087cb0c33fe8 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98455 Analysis date: Fri, 23 Oct 2026 20:17:52 -0400 ActionableScore: 1 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: A stale RFCOMM deferred-setup flag can allow RFCOMM_CONNINFO to dereference a NULL session after a Bluetooth peer sends DISC, causing a kernel Oops when a local process queries the accepted socket. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98455 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98455 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-98455 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98455 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'A NULL pointer dereference in the Bluetooth RFCOMM getsockopt path occurs because dlc defer_setup can remain enabled after a remote DISC removes the RFCOMM session. A later RFCOMM_CONNINFO request on the accepted socket can bypass the disconnected state check and unconditionally dereference dlc session. No race is required once the DISC has been processed. A local process holding the accepted socket can trigger the fault directly by calling getsockopt. An adjacent Bluetooth peer may also establish the required state and send DISC when a local service automatically queries RFCOMM_CONNINFO after accept. For the CVSS the PR:N value is used for the paranoid adjacent network scenario because the Bluetooth peer does not need a local account or authenticated operating system privileges. Reliable remote triggering still depends on Bluetooth reachability, BT_DEFER_SETUP, a compatible listening service, and application behavior that reaches the vulnerable getsockopt path, so AC:H is appropriate. Impact is denial of service through a kernel Oops and may become a host crash when Oops handling is fatal. The analyzed path provides a NULL dereference but no supported UAF, OOB write, information leak, or privilege escalation primitive. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.3 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE REMOTE KASAN OOB NULLPTR INIT RACE NETWORK HARDWARE LINUS MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 1 * Paranoid score: 1 * No floor or cap was applied. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Reliable kernel crash or strong DoS. The supplied KASAN trace establishes an unconditional NULL dereference and kernel Oops after the required state sequence. * No remote-reachability points. A Bluetooth peer controls the DISC transition, but the final vulnerable operation requires a local process to call `getsockopt(RFCOMM_CONNINFO)` on the accepted socket. * No local-unprivileged point. The reproducer used UID 0 and `/dev/vhci`, while the privilege requirements for a complete production trigger are not established. * No UAF points. `rfcomm_dlc_unlink()` sets `dlc->session` to NULL. The later operation dereferences NULL rather than retaining or consuming a freed session object. * No corruption or structured-state leverage points. The vulnerable operation is an invalid read through a NULL pointer at fixed offset `0x10`; it does not write through the pointer. * No extra Availability point. The Oops and possible panic are the same consequence. * No C/I, controlled reclaim, arbitrary write, disclosure, repeated release, authorization bypass, or privilege-escalation signal is established. * V33, V32, V34, B5-R, B3-PENDING, and B4-PENDING do not apply. There is no attacker-influenced active-state write, checksum metadata corruption, shared-backing write, retry-accumulated OOB write, or authorization decision bypass. 3. Reachability analysis A remote BR/EDR peer can create an RFCOMM session and send DISC after deferred setup, leaving `defer_setup` set while `session` is NULL. That remote action alone does not execute the vulnerable dereference. A local application must retain the accepted socket and subsequently request `RFCOMM_CONNINFO`. The supplied reproducer uses UID 0 and an emulated peer through `/dev/vhci`, but this does not prove that host-administrator privilege is required in a real Bluetooth deployment. It also does not establish ordinary unprivileged reachability. The complete privilege boundary is therefore unknown. No evidence establishes that all required Bluetooth setup, socket operations, and virtual-controller operations are available through attacker-created user or network namespaces. There is no race or narrow timing window. Once DISC has been processed, the later dereference is deterministic. 4. Primitive and severity interpretation The exact primitive is a deterministic NULL-pointer read caused by inconsistent RFCOMM connection state. `dlc->defer_setup` remains true after teardown sets `dlc->session` to NULL, so the old condition incorrectly permits the code to evaluate `dlc->session->sock->sk`. This is Class C invalid-state and crash behavior, not a use-after-free or post-lifetime structured-object operation. There is no second release, refcount mutation, stale object reuse, OOB access, or attacker-controlled write. The demonstrated consequence is a kernel Oops. A host-wide panic is possible under fatal Oops policy but does not create a separate primitive. ImportantCandidate is NO because no useful corruption or security-boundary primitive remains after excluding the crash. AutoDowngradeAllowed is YES because the defect is constrained to a NULL dereference and no unresolved exploitation leverage is established. Operational severity is ordinary Moderate or Low-like depending on whether a compatible local service automatically calls `RFCOMM_CONNINFO` and whether Oops is fatal. 5. One-sentence report phrase A stale RFCOMM deferred-setup flag can allow RFCOMM_CONNINFO to dereference a NULL session after a Bluetooth peer sends DISC, causing a kernel Oops when a local process queries the accepted socket. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Confirm whether affected products expose a Bluetooth service that automatically invokes `RFCOMM_CONNINFO` after accept and whether that complete path is reachable below host-administrator privilege. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: Bluetooth: RFCOMM: fix NULL dereference of dlc->session in RFCOMM_CONNINFO Commit: c3aee3fc1287c8a555baf3895959087cb0c33fe8 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c3aee3fc1287c8a555baf3895959087cb0c33fe8 Commit description: The RFCOMM_CONNINFO getsockopt handler accepts a socket that is not connected as long as deferred setup is enabled: if (sk->sk_state != BT_CONNECTED && !rfcomm_pi(sk)->dlc->defer_setup) { err = -ENOTCONN; break; } l2cap_sk = rfcomm_pi(sk)->dlc->session->sock->sk; dlc->defer_setup is set in rfcomm_sock_init() when rfcomm_connect_ind() creates a child socket for an incoming connection on a listening socket that has BT_DEFER_SETUP enabled. It is never cleared afterwards. The session, however, can go away underneath it. rfcomm_recv_disc() forces the dlc state before tearing it down: d->state = BT_CLOSED; __rfcomm_dlc_close(d, err); The RFCOMM_DEFER_SETUP early return in __rfcomm_dlc_close() only covers BT_CONNECT, BT_CONFIG, BT_OPEN and BT_CONNECT2, so with the state already BT_CLOSED that switch does not match and the function falls through to rfcomm_dlc_unlink(), which sets d->session = NULL, while d->defer_setup stays 1. A getsockopt(SOL_RFCOMM, RFCOMM_CONNINFO) on the accepted socket after that point therefore skips the -ENOTCONN path -- sk->sk_state is BT_CLOSED, but dlc->defer_setup is still set -- and dereferences the NULL session. No race is needed: once the DISC has been processed, the dereference is unconditional. Reproduced on a KASAN kernel under QEMU with a BR/EDR peer emulated over /dev/vhci: the peer brings up an ACL link, opens L2CAP on the RFCOMM PSM, starts a session and sends SABM for a channel bound with BT_DEFER_SETUP, and sends DISC for that dlci after the socket has been accepted. getsockopt(SOL_RFCOMM, RFCOMM_CONNINFO) on the accepted socket then hits: Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002: 0000 [#1] SMP KASAN PTI KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017] CPU: 1 UID: 0 PID: 150 Comm: init Tainted: G B 7.3.0-rc3-g5dd1818b15d9 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) RIP: 0010:rfcomm_sock_getsockopt+0x529/0x780 Call Trace: do_sock_getsockopt+0x3ad/0x7d0 __sys_getsockopt+0x10e/0x1b0 __x64_sys_getsockopt+0xc2/0x160 do_syscall_64+0xda/0x4b0 entry_SYSCALL_64_after_hwframe+0x77/0x7f 0x10 is the offset of sock in struct rfcomm_session; rfcomm_sock_getsockopt_old() is inlined into rfcomm_sock_getsockopt(). Commit 43a556b ("Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept") fixed the same "a remote DISC clears the session while deferred setup is still flagged" problem in rfcomm_dlc_accept(); this is the remaining instance of it, in the getsockopt path. Deferred setup only leaves a socket usable here once it has reached BT_CONNECT2, so restrict the exception to that state and check that a session is actually present before following it. Fixes: bb23c0a ("Bluetooth: Add support for deferring RFCOMM connection setup") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Hui Peng Signed-off-by: Luiz Augusto von Dentz Signed-off-by: Greg Kroah-Hartman Changed files: net/bluetooth/rfcomm/sock.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=c3aee3fc1287c8a555baf3895959087cb0c33fe8 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98455 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98455 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:L/PR:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.3 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: unknown Paranoid ActionableScore: 1 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).