From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74677][MODERATE 7.0] net: usb: ipheth: fix carrier_work UAF on disconnect Date: Sat, 22 Aug 2026 16:13:58 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74677 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: d07133fe1befae9a1e4c4c5e46ef0b73d2992020 List-Id: CVE: CVE-2026-74677 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: net: usb: ipheth: fix carrier_work UAF on disconnect Commit: d07133fe1befae9a1e4c4c5e46ef0b73d2992020 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d07133fe1befae9a1e4c4c5e46ef0b73d2992020 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74677 Analysis date: Sat, 22 Aug 2026 16:13:58 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A race in the ipheth USB network driver can re-arm carrier_work after close or disconnect, leaving delayed work pending after free_netdev and causing a confirmed slab-use-after-free that is realistically a local or device-mediated kernel crash DoS. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74677 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74677 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. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74677 MODERATE CHECK WITH IMPACT FROM ORIG NN 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:L/I:L/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A use after free can occur in the ipheth USB network driver because carrier_work can be re armed by ipheth_sndbulk_callback after ipheth_close has already drained the delayed work. During disconnect, an in flight TX URB may complete with an error after unregister_netdev and ipheth_close, which can queue carrier_work again while the netdev private area that embeds the work item is later freed. A later timer or workqueue execution can dereference freed memory and crash the kernel. For the CVSS the PR:L is used for the paranoid score because a reduced local actor with delegated device or network control may be able to influence interface state and disconnect timing, even though the reported reproducer was driven as root. The issue is not network reachable in the normal IP packet sense and usually requires local USB device interaction or local control of the affected interface. Impact is at least local denial of service via kernel crash and in worst case may allow limited confidentiality or integrity impact due to the UAF class, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) YES USB UAF NETWORK HARDWARE LINUS KPANIC KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS NO NO 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: * Memory corruption, weak primitive: +1 Confirmed race-dependent slab-use-after-free, but no demonstrated reclaim, overwrite, attacker-controlled replacement, or LPE primitive. * Real lifetime corruption: +1 Delayed work can survive netdev teardown and later dereference freed netdev private data. * Reliable kernel crash / strong DoS: +1 KASAN reproducer reports 15 of 15 unpatched boots hitting slab-use-after-free. * Firmware-mediated or device-mediated external influence: +1 Trigger depends on behavior of an attached USB device and URB completion timing. * Privileged kernel/device-management lifetime path: +1 The bug is in USB network driver disconnect/open/close lifetime management. * Requires admin/root/CAP-like control in demonstrated path: -2 The reproducer is driven as root and needs link down plus unplug/device control. Paranoid adjustment: * Local reduced-privilege or delegated-control trigger concern: +1 In some environments, a local actor with delegated device or network-interface control may influence interface state and disconnect timing without full host-root equivalence. * Race-UAF cap applied. Conservative score is capped at 4 and paranoid score at 5 because this is a race-dependent UAF without a demonstrated controlled reclaim, write-after-free, object replacement, or privilege escalation primitive. ## 3. Reachability analysis The bug is not remotely reachable through normal IP packet traffic. Realistic triggering requires an affected ipheth USB network device, a TX URB in flight, interface close or link-down state, and disconnect or unplug timing that lets the URB completion re-arm carrier_work after it was drained. The supplied reproducer uses dummy_hcd and raw-gadget and is explicitly described as root-driven. Namespaces or containers may matter only if device or network-interface management is delegated. A normal unprivileged local user typically cannot control USB disconnect and ipheth interface state reliably. However, reduced-capability root, container root with delegated device access, or a service managing USB networking could make PR:L a defensible paranoid interpretation. ## 4. Severity interpretation This is more than an ordinary cleanup bug because the patch fixes a confirmed UAF in delayed work lifetime management. Realistic impact is mainly local DoS through kernel crash. Theoretical memory-corruption concern exists because the callback runs after the embedded work item and netdev private area are freed, but the available evidence does not show attacker-controlled reclaim, overwrite, type confusion, or privilege escalation. This should be treated as an Actionable Moderate at minimum rather than auto-closed. It is not a strong Important candidate on the supplied evidence because exploitation needs local or physical/device control and no concrete privilege-escalation primitive was developed. ## 5. One-sentence report phrase A race in the ipheth USB network driver can re-arm carrier_work after close or disconnect, leaving delayed work pending after free_netdev and causing a confirmed slab-use-after-free that is realistically a local or device-mediated kernel crash DoS. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: confirmed UAF plus async workqueue lifetime mismatch. No demonstrated LPE primitive is present, but the bug class and reliable KASAN reproduction make it inappropriate for automatic closure. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net: usb: ipheth: fix carrier_work UAF on disconnect Commit: d07133fe1befae9a1e4c4c5e46ef0b73d2992020 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d07133fe1befae9a1e4c4c5e46ef0b73d2992020 Commit description: ipheth_sndbulk_callback() re-arms the carrier-check work on any non-zero URB status: else schedule_delayed_work(&dev->carrier_work, 0); Nothing ties that to the interface being up, so the work can be armed again after ipheth_close() has already drained it, and stay armed until the netdev whose private area embeds it is freed. On unplug with a TX URB in flight, ipheth_disconnect() drains the work through unregister_netdev() -> ipheth_close() -> cancel_delayed_work_sync() and only then calls ipheth_kill_urbs(). usb_kill_urb() completes the in-flight TX URB with -ENOENT, so ipheth_sndbulk_callback() runs after the drain and re-arms carrier_work. The same completion also re-arms the work if the interface is only brought down while a TX URB is in flight, and ipheth_carrier_check_work() then keeps re-queueing itself once a second. unregister_netdev() does not call ipheth_close() for an already-down interface, so nothing drains it on the later unplug either. In both cases free_netdev() frees the netdev while carrier_work is still pending, and ipheth_carrier_check_work() dereferences freed memory. Tie the work to the interface state instead of chasing the completion: disable it in ipheth_close() and enable it in ipheth_open(), so a schedule_delayed_work() from the URB completion is a no-op whenever the interface is not up. disable_delayed_work_sync() also waits for a running instance, so it fully replaces the cancel_delayed_work_sync() it takes the place of. The work starts out disabled in ipheth_probe() so the enable/disable counts balance from the first open. Reproduced under KASAN on linux-next (next-20260731) with dummy_hcd and raw-gadget standing in for the device, driving the second path above (the interface is already down, so unregister_netdev() does not call ipheth_close()): 15 of 15 unpatched boots report a slab-use-after-free in __run_timers(), freed by ipheth_disconnect() and re-armed from ipheth_sndbulk_callback() via queue_delayed_work_on(). The same trigger on a kernel differing only by this patch reports 0 of 15, and the carrier check still functions across open/close cycles. The reproducer needs an attached USB device that stops draining bulk OUT, plus a link down and unplug, driven as root. It is not a privilege boundary crossing and no exploit primitive was developed. Found by 0sec ( https://0sec.ai ). Fixes: bb1b40c ("usbnet: ipheth: prevent TX queue timeouts when device not ready") Cc: stable@vger.kernel.org Signed-off-by: Doruk Tan Ozturk Link: https://patch.msgid.link/20260802120602.42595-1-doruk@0sec.ai Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: drivers/net/usb/ipheth.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=d07133fe1befae9a1e4c4c5e46ef0b73d2992020 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74677 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74677 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:H/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:L/I:L/A:H The Best / paranoid CVSS score: 5.8 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).