From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46186][MODERATE 7.0] Bluetooth: virtio_bt: validate rx pkt_type header length Date: Thu, 28 May 2026 10:23:09 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46186 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: 1e1e509b6fd2a42421745bbcd98bd16daad20904 List-Id: CVE: CVE-2026-46186 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: Bluetooth: virtio_bt: validate rx pkt_type header length Commit: 1e1e509b6fd2a42421745bbcd98bd16daad20904 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1e1e509b6fd2a42421745bbcd98bd16daad20904 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46186 Analysis date: Thu, 28 May 2026 10:23:09 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: NO Summary: `virtbt_rx_handle()` failed to validate per-type HCI header lengths after stripping `pkt_type`, allowing an untrusted virtio Bluetooth backend to send short packets that trigger invalid or uninitialized reads in the guest HCI stack. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46186 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46186 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-46186 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-457;*CWE-20;CWE-754;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '6.4';DESCR 'virtio_bt accepted backend supplied RX packets after only reading the leading pkt_type byte and did not verify that the remaining payload contained the fixed HCI header required for the selected packet type. A malicious or compromised virtio Bluetooth backend can return a one byte completion so the skb length becomes zero after skb_pull, while hci_recv_frame still receives the frame and later HCI code may read uninitialized RX buffer bytes. For the CVSS the PR:N is used because the attacker is the backend or host side of the virtio device and does not need privileges inside the victim guest. The issue is not Internet reachable but can cross a host guest virtualization boundary when virtio Bluetooth is exposed. Impact is primarily guest availability through crash or malformed HCI processing, with limited confidentiality concern from uninitialized data reads and no supported arbitrary write or direct privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) MAYBE VIRT ERRORPATH SKB HARDWARE PACKET KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: 4 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Firmware/backend-mediated external influence: +1. The input is supplied by an untrusted virtio Bluetooth backend rather than by local guest userspace. * Weak/indirect corruption candidate: +1. The bug causes invalid or uninitialized reads after short HCI packets are passed into the core. * Reliable kernel crash / strong DoS: +1. Short packets can reach HCI parsing paths and may cause guest kernel faults or malformed HCI processing. * Availability impact realistic: +1. Guest Bluetooth stack or guest kernel availability can be affected. Paranoid additional signal: * Cross-boundary isolation impact: +1. The bug crosses a host/backend to guest boundary when virtio Bluetooth is exposed. Not counted: * No generic memory corruption. The primitive is read-only invalid/uninitialized access. * No OOB write, UAF, double free, arbitrary write, or demonstrated LPE. * No Internet/network reachability. * Confidentiality impact is limited and not scored strongly because the described read is internal classification of uninitialized RX-buffer bytes, not a clear leak to the attacker. ## 3. Reachability analysis A malicious or compromised virtio Bluetooth backend can supply a too-short RX completion to the guest. The guest does not need to run attacker-controlled local code, and the attacker does not need privileges inside the guest if they control the backend side. This is not reachable from ordinary Bluetooth radio traffic or the Internet by itself. It is relevant to virtualized environments where virtio Bluetooth is exposed and the backend is less trusted than the guest. The trigger may require specific HCI state for the described ACL fast path, such as active CIS, BIS, or PA links, but the missing per-type header validation affects all accepted packet types. ## 4. Severity interpretation This behaves like an actionable Moderate virtualization-boundary input validation issue. The realistic impact is guest DoS or malformed Bluetooth/HCI processing. It does not behave like an Important memory-corruption issue because the patch supports invalid or uninitialized reads, not controlled writes, UAF, or a demonstrated privilege escalation chain. ## 5. One-sentence report phrase `virtbt_rx_handle()` failed to validate per-type HCI header lengths after stripping `pkt_type`, allowing an untrusted virtio Bluetooth backend to send short packets that trigger invalid or uninitialized reads in the guest HCI stack. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Manual review is recommended for deployments exposing virtio Bluetooth across host/guest trust boundaries, but current evidence supports guest availability and limited read concerns only, not LPE or arbitrary memory corruption. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: Bluetooth: virtio_bt: validate rx pkt_type header length Commit: 1e1e509b6fd2a42421745bbcd98bd16daad20904 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1e1e509b6fd2a42421745bbcd98bd16daad20904 Commit description: virtbt_rx_handle() reads the leading pkt_type byte from the RX skb and forwards the remainder to hci_recv_frame() for every event/ACL/SCO/ISO type, without checking that the remaining payload is at least the fixed HCI header for that type. After the preceding patch bounds the backend-supplied used.len to [1, VIRTBT_RX_BUF_SIZE], a one-byte completion still reaches hci_recv_frame() with skb->len already pulled to 0. If the byte happened to be HCI_ACLDATA_PKT, the ACL-vs-ISO classification fast-path in hci_dev_classify_pkt_type() dereferences hci_acl_hdr(skb)->handle whenever the HCI device has an active CIS_LINK, BIS_LINK, or PA_LINK connection, reading two bytes of uninitialized RX-buffer data. The same hazard exists for every packet type the driver accepts because none of the switch cases in virtbt_rx_handle() check skb->len against the per-type minimum HCI header size before handing the frame to the core. After stripping pkt_type, require skb->len to cover the fixed header size for the selected type (event 2, ACL 4, SCO 3, ISO 4) before calling hci_recv_frame(); drop ratelimited otherwise. Unknown pkt_type values still take the original kfree_skb() default path. Use bt_dev_err_ratelimited() because both the length and pkt_type values come from an untrusted backend that can otherwise flood the kernel log. Fixes: 160fbcf ("Bluetooth: virtio_bt: Use skb_put to set length") Cc: stable@vger.kernel.org Cc: Soenke Huster Signed-off-by: Michael Bommarito Assisted-by: Claude:claude-opus-4-7 Signed-off-by: Luiz Augusto von Dentz Signed-off-by: Greg Kroah-Hartman Changed files: drivers/bluetooth/virtio_bt.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=1e1e509b6fd2a42421745bbcd98bd16daad20904 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46186 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46186 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:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 6.4 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).