From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98735][IMPORTANT] Bluetooth: hci_core: Serialize ACL scheduling with channel deletion Date: Sat, 24 Oct 2026 10:26:57 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98735 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 51f95ea451f25d7e3f048c0f438f04fa74688aae List-Id: CVE: CVE-2026-98735 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: NO Patch: Bluetooth: hci_core: Serialize ACL scheduling with channel deletion Commit: 51f95ea451f25d7e3f048c0f438f04fa74688aae Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=51f95ea451f25d7e3f048c0f438f04fa74688aae Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98735 Analysis date: Sat, 24 Oct 2026 10:26:57 -0400 ActionableScore: 5 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: A timing-sensitive L2CAP teardown race frees an active HCI channel before TX finishes using its queue and counters, causing a confirmed structured-object UAF. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98735 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98735 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-2026-98735 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-98735 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT IMPORTANT AEGIS_AS=6 LEGACY=IMPORTANT RESULT=SAME INDEPENDENT_LEGACY=MODERATE_KPANIC INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_HARD_VETO PRE_MERGE_LEGACY=MODERATE_KPANIC (final reconciliation agrees; DECISION: both IMPORTANT) 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:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race allows hci_chan_sent to return a channel after dropping its RCU read lock while a disconnect timeout on another workqueue can unlink and free the same channel. The ACL or LE scheduler can then access the freed packet queue and update transmit state, producing a confirmed slab use after free with potential reads and writes to reused kernel memory. For the CVSS the PR:L value reflects that reliable triggering normally requires a local user or process able to create and operate a Bluetooth L2CAP connection. AC:H reflects the required timing window between transmission scheduling and asynchronous channel teardown. Impact is at least a local denial of service through a kernel crash and the confirmed use after free provides a plausible memory corruption path that may affect confidentiality or integrity. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because FD false positive review allowed a downgrade. final reconciliation stage MODERATE_KPANIC to IMPORTANT because a specific evidence based protection or manual review veto was applied and KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH and TEMP_KPANIC_MERGE_IMPORTANT_VETO and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 3.6 and ActionableScore 6 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was IMPORTANT. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE REMOTE DANGER UAF NETWORK HARDWARE LINUS PACKET INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH TEMP_KPANIC_MERGE_IMPORTANT_VETO KPANIC_UNSUPPORTED_REMOVED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=NO NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 4. * Conservative score: 5. REAL UAF FLOOR 5 applies because below-host-admin reachability and nontrivial active-object processing of the freed channel are supported. * Raw paranoid score: 5. * Paranoid score: 5. No further cap or floor adjustment. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 — Confirmed UAF: `hci_chan_sent()` returns `chan` after leaving RCU; concurrent teardown completes `synchronize_rcu()`, purges, and frees it before scheduler use. * +1 — Reliable crash/DoS concern: KASAN confirms slab use-after-free in `hci_chan_sent()`. * +1 — Local below-host-admin trigger: supplied evidence grounds a local process creating and operating an L2CAP connection. * +1 — Structured stale-object leverage: callers inspect `chan->data_q`, submit packets, and update transmit counters after possible free. This is active processing beyond a cleanup-only dereference. * -1 — Hard timing: the trigger requires an interleaving between TX scheduling and asynchronous disconnect-timeout teardown. * Paranoid +1 — The local actor controls connection creation, queued traffic, and repeated operation attempts, providing a defensible stronger reading of lifetime-transition influence. Not awarded: controlled reclaim, attacker-shaped replacement contents, arbitrary/directed write, disclosure, LPE, or C/I impact. The same crash receives no additional availability point. This is not B5-R: no retry-accumulated heap OOB write is shown. 3. Reachability analysis A local process able to create and operate a Bluetooth L2CAP connection can populate the channel and exercise TX while timeout processing deletes it. The evidence supports reduced local privilege rather than host-administrator authority; host UID 0 is not required. No namespace capability chain is established. Bluetooth hardware and a usable connection are prerequisites, but the evidence does not establish rare hardware or prior privileged setup. Repeated attempts are possible, although the critical workqueue interleaving remains timing-sensitive. 4. Primitive and severity reading The primitive is a confirmed UAF of an active structured `hci_chan`, not fixed stale storage. Teardown unlinks and frees the channel after the selector drops RCU protection; TX subsequently reads its queue and updates transmit state. This is broader active use, not merely a destructor fault, but no controlled reclaim or useful replacement object is shown. It is therefore CLASS_B, not CLASS_A. The demonstrated result is sanitizer-detected post-free access with plausible kernel crash and fixed-offset writes into potentially reused slab storage. Exploitation beyond crash remains unresolved. ImportantCandidate is YES and automatic downgrade is disallowed because attacker-influenced active structured state is consumed and modified after free. 5. One-sentence report phrase A timing-sensitive L2CAP teardown race frees an active HCI channel before TX finishes using its queue and counters, causing a confirmed structured-object UAF. 6. Manual review advice MANUAL CHECK REQUIRED Review reclaim behavior, exact post-free counter writes, allocator reuse, and practical race control before deciding Important versus Actionable Moderate. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: Bluetooth: hci_core: Serialize ACL scheduling with channel deletion Commit: 51f95ea451f25d7e3f048c0f438f04fa74688aae Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=51f95ea451f25d7e3f048c0f438f04fa74688aae Commit description: hci_chan_sent() selects a channel under RCU but drops the read lock before accessing chan->conn and returning the channel. The ACL and LE schedulers then use its packet queue and update its transmit counters without any protection against channel deletion. After TX selects a channel and releases RCU, a disconnect command timeout on the separate request workqueue can run hci_conn_failed() and l2cap_conn_del(). hci_chan_del() can then unlink the channel, complete synchronize_rcu(), purge its queue and free it before TX resumes. This causes use-after-free both in hci_chan_sent() and in its callers. KASAN reported: BUG: KASAN: slab-use-after-free in hci_chan_sent+0x892/0x9b0 Workqueue: hci0 hci_tx_work Call Trace: hci_chan_sent+0x892/0x9b0 hci_tx_work+0x5e6/0xb70 Allocated by task 91: hci_chan_create+0xe3/0x350 l2cap_conn_add.part.0+0x12/0xa30 l2cap_chan_connect+0x110d/0x1b60 l2cap_sock_connect+0x310/0x530 Freed by task 99: hci_chan_del+0x11f/0x170 l2cap_conn_del+0x4f1/0x800 l2cap_connect_cfm+0x88c/0xd30 hci_conn_failed+0x150/0x250 hci_abort_conn_sync+0x3e3/0x800 hci_cmd_sync_run+0x7e/0xc0 hci_abort_conn+0x105/0x1f0 disconnect_sync+0x157/0x290 hci_cmd_sync_work+0x13c/0x290 Hold the existing device mutex across channel selection and transmission in both schedulers to serialize them with channel teardown. Keep timeout handling outside the critical sections because hci_link_tx_to() acquires the same mutex. This also permits the transmit path to sleep, unlike extending the RCU read-side critical section across packet submission. Fixes: 3eff45e ("Bluetooth: convert tx_task to workqueue") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Chengfeng Ye Signed-off-by: Luiz Augusto von Dentz Signed-off-by: Greg Kroah-Hartman Changed files: net/bluetooth/hci_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=51f95ea451f25d7e3f048c0f438f04fa74688aae ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98735 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98735 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: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: unknown 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: IMPORTANT KPANIC detected for this report: NO 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 alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).