From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-68194][MODERATE REGULAR] wifi: mt76: mt7921: drop TXRX_NOTIFY on non-mmio buses Date: Mon, 10 Aug 2026 08:59:21 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-68194 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: 3 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: ef2ee5f820c3ef87643b51e960c20b4a14d8336b List-Id: CVE: CVE-2026-68194 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: wifi: mt76: mt7921: drop TXRX_NOTIFY on non-mmio buses Commit: ef2ee5f820c3ef87643b51e960c20b4a14d8336b Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ef2ee5f820c3ef87643b51e960c20b4a14d8336b Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68194 Analysis date: Mon, 10 Aug 2026 08:59:21 -0400 ActionableScore: 3 ActionableScore lower bound: 1 Actionable bucket: Borderline Moderate. Manual triggerability review recommended Manual review required: NO Summary: A non-MMIO mt7921 USB or SDIO device can receive an MMIO-only TXRX_NOTIFY event that reaches mt7921_mac_tx_free() and calls a NULL tx_cleanup callback, causing a kernel crash through the RX worker. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68194 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68194 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-2026-68194 MODERATE CHECK WITH IMPACT FROM ORIG NN MODERATE 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-754;CWE-703;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'A NULL pointer dereference can occur in the mt7921 RX path because PKT_TYPE_TXRX_NOTIFY is handled on non MMIO buses even though only MMIO queue operations provide the tx_cleanup callback. On USB or SDIO devices this can route RX worker processing into mt7921_mac_tx_free and mt76_queue_tx_cleanup with queue_ops tx_cleanup set to NULL, causing a kernel crash. For the CVSS the PR:N is used in the paranoid score because the higher risk interpretation assumes the attacker can trigger or provide the device side event without a local account on the target. The issue is not directly reachable through normal IP packet processing. Practical exploitation likely requires a malicious or faulty USB or SDIO WiFi device, compromised firmware, or a still unproven adjacent WiFi condition that causes the device to emit this MMIO only event. Impact is denial of service only via kernel crash, with no supported evidence of memory corruption, information disclosure, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate. Manual triggerability review recommended (with actual score 2) YES REMOTE DANGER NULLPTR INIT SIMPLEFIX NETWORK SKB DMAorINTERRUPT HARDWARE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=1 ## 1. ActionableScore * Conservative score: 1 * Paranoid score: 3 * Final recommended bucket: **Borderline Moderate. Manual triggerability review recommended**:: ## 2. Signal breakdown Conservative signals: * Reliable kernel crash / strong DoS: +1. The patch and trace show a NULL function pointer call through queue_ops->tx_cleanup in the RX worker, causing a kernel NULL pointer dereference. * Rare / difficult-to-reach condition: -1. The affected path is limited to mt7921 non-MMIO devices, mainly USB or SDIO, and requires an MMIO-only TXRX_NOTIFY event to appear on that bus. * Firmware-mediated external influence: +1. The event is device or firmware mediated rather than normal IP packet processing. Conservative total: 1. Paranoid additional signals: * Availability impact realistic: +1. If a faulty, malicious, or compromised device or firmware can emit the event reliably, the result is a host-wide kernel crash. * Broad/common driver class exposure: +1. WiFi drivers are common, and mt76/mt7921 devices are realistic deployed hardware, even though this exact bus/event combination is narrower. Paranoid total: 3. Not counted: * No remote reachable / network-triggerable +2. The patch does not show that normal WiFi frames or IP traffic can directly generate PKT_TYPE_TXRX_NOTIFY. * No local unprivileged trigger +1. No ordinary local user API is shown for generating this RX event. * No generic memory corruption +2. This is a NULL callback invocation, not UAF, OOB write, double free, type confusion, or arbitrary write. * No privilege escalation plausible +2. There is no supported reclaim, overwrite, callback control, or object confusion primitive. * No confidentiality or integrity impact. The observed impact is crash only. ## 3. Reachability analysis The realistic trigger is a non-MMIO mt7921 device path, such as USB or SDIO, receiving PKT_TYPE_TXRX_NOTIFY even though that event is intended for MMIO devices only. The event is handled in mt7921_rx_check() or mt7921_queue_rx_skb(), then routed to mt7921_mac_tx_free(), which reaches a NULL tx_cleanup callback. A normal remote IP network attacker is not clearly able to trigger this. A practical trigger likely requires a faulty device, malicious USB or SDIO device behavior, compromised firmware, or possibly an adjacent WiFi condition that causes firmware to emit the unexpected event. That adjacent RF triggerability is not demonstrated by the patch. Namespaces and containers do not materially lower privileges here because the trigger is not a regular local syscall or netlink control path. The vulnerable code can be present in ordinary systems using affected mt7921 USB or SDIO hardware, but the exact event condition is specialized. Call-site confidence: high. The patch and commit provide both the relevant call path and the concrete NULL callback failure mode. ## 4. Severity interpretation This behaves more like a Low-like or ordinary Moderate DoS issue under conservative assumptions. It becomes a borderline actionable Moderate only under the paranoid interpretation where device-side or firmware-mediated triggering is realistic. Theoretical memory corruption potential is weak. A NULL function pointer call is a crash primitive, not a demonstrated memory corruption or LPE primitive. Realistic exploitation evidence supports kernel DoS, not privilege escalation or data exposure. ## 5. One-sentence report phrase A non-MMIO mt7921 USB or SDIO device can receive an MMIO-only TXRX_NOTIFY event that reaches mt7921_mac_tx_free() and calls a NULL tx_cleanup callback, causing a kernel crash through the RX worker. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: the bug is likely DoS-only, but manual review is useful to confirm whether TXRX_NOTIFY can be induced by adjacent WiFi activity, firmware behavior, or only by faulty or malicious device-side conditions. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: wifi: mt76: mt7921: drop TXRX_NOTIFY on non-mmio buses Commit: ef2ee5f820c3ef87643b51e960c20b4a14d8336b Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ef2ee5f820c3ef87643b51e960c20b4a14d8336b Commit description: PKT_TYPE_TXRX_NOTIFY is an mmio-only event, but mt7921_rx_check() and mt7921_queue_rx_skb() dispatch it to mt7921_mac_tx_free() on every bus. mt7921_mac_tx_free() cleans the DMA tx queues with mt76_queue_tx_cleanup(), which calls queue_ops->tx_cleanup(). Only the mmio queue ops implement that callback; on USB and SDIO it is NULL, so a TXRX_NOTIFY there calls a NULL pointer in the RX worker: BUG: kernel NULL pointer dereference, address: 0000000000000000 RIP: 0010:0x0 Call Trace: mt7921_mac_tx_free+0x64/0x310 [mt7921_common] mt7921_rx_check+0x5f/0xf0 [mt7921_common] mt76u_rx_worker+0x1b9/0x620 [mt76_usb] Drop the event on non-mmio buses via mt76_is_mmio(), as in commit 5683e14 ("wifi: mt76: connac: do not check WED status for non-mmio devices"). Fixes: 48fab5b ("mt76: mt7921: introduce mt7921s support") Cc: stable@vger.kernel.org Signed-off-by: Devin Wittmayer Link: https://patch.msgid.link/20260627191336.20223-2-lucid_duck@justthetip.ca Signed-off-by: Felix Fietkau Signed-off-by: Greg Kroah-Hartman Changed files: drivers/net/wireless/mediatek/mt76/mt7921/mac.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=ef2ee5f820c3ef87643b51e960c20b4a14d8336b ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68194 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68194 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:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H 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: 1 Paranoid ActionableScore: 3 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).