From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-81001][MODERATE 7.0] slip: fix use-after-free in sl_sync() Date: Fri, 11 Sep 2026 16:55:10 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-81001 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: a235b20972bbd98ca1fb127d6269434edc607f19 List-Id: CVE: CVE-2026-81001 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: slip: fix use-after-free in sl_sync() Commit: a235b20972bbd98ca1fb127d6269434edc607f19 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a235b20972bbd98ca1fb127d6269434edc607f19 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-81001 Analysis date: Fri, 11 Sep 2026 16:55:10 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-81001 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-81001 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-2026-81001 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-81001 CHECK WITH IMPACT FROM ORIG NN MODERATE 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:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in the SLIP driver can leave a stale net_device pointer visible in the slip_devs table while netdev_run_todo() runs priv_destructor and releases the device without RTNL serialization. A local attacker can trigger the race by repeatedly opening a pseudo tty, switching it to the N_SLIP line discipline, and closing it, causing sl_sync() or slip_open() to dereference freed memory. For the CVSS the PR:L is used because reliable triggering requires local code execution and likely network administration capability such as CAP_NET_ADMIN, but not full host root in all delegated or containerized environments. The issue is not network reachable through packet traffic and is triggered through a local tty control path. Impact is at least denial of service via kernel crash, and the use-after-free on a kernel object makes privilege escalation theoretically plausible enough for manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) YES READ OOB DANGER INIT RACE ERRORPATH UAF NETWORK HARDWARE KPANIC NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 3 * Conservative score: 4 * Raw paranoid score: 4 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: Conservative floor applied: 3 -> 4 because a real active-object UAF is established and host-admin-equivalent privilege is not positively established. Paranoid floor applied: 4 -> 5 because the stale object is an active `net_device` / SLIP private object, the attacker can repeatedly drive the relevant open and close lifecycle, and the stale use occurs in the active `slip_open()` / `sl_sync()` path rather than only in final cleanup. 2. Signal breakdown Positive signals: * +2 Real UAF / active lifetime violation. `sl_sync()` can read `slip_devs[i]` while it still contains a bare `net_device` pointer, then `netdev_run_todo()` can run the destructor and free the device before `sl_sync()` dereferences it. * +1 Reliable kernel crash / strong DoS. KASAN shows a real use-after-free read in `sl_sync()` / `slip_open()`, and this is a realistic kernel crash condition. * +1 paranoid attacker-influenced active-object lifetime manipulation. The reproduced trigger repeatedly performs `open("/dev/ptmx")`, `ioctl(TIOCSETD, N_SLIP)`, and `close()`, driving SLIP netdevice allocation, teardown, and stale lookup attempts. Negative signals: * No host-admin penalty applied. The exact complete privilege boundary is not fully established by the supplied patch text. `N_SLIP` setup may involve `CAP_NET_ADMIN`, but the evidence here does not prove host-admin-equivalent privilege for the complete trigger. * No race penalty applied. Although this is a race, the supplied reproducer uses repeated local operations and the race is not shown to be one-shot or externally uncontrollable. * No rare-subsystem penalty applied. SLIP is legacy/specialized, but the reproducer can instantiate the relevant path through pty and line-discipline operations. Important non-awarded signals: * Controlled reclaim not demonstrated. * Arbitrary kernel read/write not demonstrated. * Callback or function-pointer control not demonstrated. * Remote network reachability not established. This is networking code, but the trigger is a local TTY line-discipline path, not packet traffic. * C/I impact not awarded as direct signals. The demonstrated behavior is UAF and crash, while confidentiality or integrity impact remains unresolved rather than proven. * Concrete repeated release/refcount signal not awarded. The first lifetime end is via `kobject_put()` / device release, but the later stale operation shown is a dereference/read through `netdev_priv(dev)`, not a second `put`, `free`, or refcount mutation on the same dangling reference. * Structured stale-object leverage not separately awarded. The stale object is structured, but no distinct attacker-shaped replacement, callback use, pointer traversal, or security-sensitive field consumption is established beyond the counted active lifetime manipulation. * Extra availability point not awarded because the same crash is already counted once. Repeated-release/refcount checklist: * First release can end lifetime: yes, `kobject_put()` can release the network device. * Exact same reference survives: yes, `sl_sync()` may retain the bare pointer loaded from `slip_devs[]`. * Second operation is a real lifetime/refcount mutation: no, the demonstrated second operation is stale dereference/read. * +1 Concrete repeated release/refcount awarded: no. * Paranoid repeated-refcount leverage +1 awarded: no. * FLOOR 5 applied: yes, but for active-object UAF with repeatable lifecycle manipulation, not for repeated refcount mutation. 3. Reachability analysis The demonstrated trigger is local. The supplied reproducer uses multiple threads looping over pty creation, switching the TTY line discipline to `N_SLIP`, and closing the file descriptor. Ordinary unprivileged reachability is not fully proven from the supplied context. The pty operations are commonly reachable by local users, but setting networking line disciplines such as SLIP may require `CAP_NET_ADMIN` depending on the exact kernel path and configuration. Because the complete privilege boundary is not resolved here, `HostAdminRequired=UNKNOWN` is used rather than assuming either ordinary-user access or host-admin-only access. Namespace-scoped privilege is also unresolved. The presence of networking code does not prove that all required stages can be completed with attacker-created namespace capabilities. No prior privileged host setup is clearly required by the patch text, but capability gating for `N_SLIP` is material and should be checked in the target kernel. No direct network trigger is established. Packets sent to a SLIP interface are not the described trigger. The vulnerable operation is reached through local TTY control operations and netdevice teardown. The race appears repeatable because the attacker can repeatedly drive open and close operations. It is not treated as a hard one-shot race. 4. Primitive and severity interpretation The exact primitive is a real use-after-free on a `net_device` pointer stored in the global `slip_devs[]` table without a reference. The object is active structured kernel state, not fixed stale DMA/URB storage. This is not merely a destructor-only stale dereference. The stale read occurs when `sl_sync()` / `slip_open()` walks the global table while another path can unregister and free the device after RTNL has been dropped by `netdev_run_todo()`. The demonstrated consequence is kernel memory-safety violation with crash/DoS. The speculative consequence is local privilege escalation if the stale `net_device` / SLIP-private memory can be reclaimed or shaped in a useful way, but controlled reclaim and a concrete non-crash exploitation chain are not established by the supplied evidence. Primitive class is `CLASS_B`: a real kernel lifetime/UAF primitive exists, but no controlled reclaim, arbitrary write, refcount takeover, callback hijack, or demonstrated LPE is shown. ImportantCandidate is `YES` because this is an active-object UAF reachable through a repeatable local lifecycle sequence, and the Important-vs-Moderate exploitation leverage remains unresolved. AutoDowngradeAllowed is `NO` because automatically treating this as an ordinary crash-only issue would discard a concrete kernel lifetime primitive with unresolved exploitation leverage. It is not proven Important, but it should not be auto-closed. Likely operational severity is actionable Moderate at minimum, with manual review needed for possible Important classification. 5. One-sentence report phrase A race in the SLIP driver can leave a stale `net_device` pointer in `slip_devs[]`, allowing local TTY line-discipline operations to trigger a use-after-free in `sl_sync()` / `slip_open()` and cause a kernel crash, with unresolved privilege-escalation potential requiring manual review. 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a confirmed kernel use-after-free on active networking object state, reachable through repeatable local lifecycle operations, and the available evidence does not rule out exploitation beyond DoS. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: slip: fix use-after-free in sl_sync() Commit: a235b20972bbd98ca1fb127d6269434edc607f19 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a235b20972bbd98ca1fb127d6269434edc607f19 Commit description: slip_devs[] stores bare net_device pointers and takes no reference on them. sl_sync() and sl_alloc() walk that table from slip_open() under rtnl_lock(), while an entry is dropped by sl_free_netdev(), which sl_setup() installs as dev->priv_destructor. priv_destructor is called from netdev_run_todo(), which deliberately runs with the RTNL semaphore released so that it can sleep while waiting for the device refcount to drop: /* Snapshot list, allow later requests */ list_replace_init(&net_todo_list, &list); __rtnl_unlock(); ... if (dev->priv_destructor) dev->priv_destructor(dev); /* slip_devs[i] = NULL */ if (dev->needs_free_netdev) free_netdev(dev); ... /* Free network device */ kobject_put(&dev->dev.kobj); So rtnl_lock() does not serialise slip_open() against the teardown at all. sl_sync() can load slip_devs[i] while the entry is still published and dereference it after netdev_run_todo() has run the destructor and released the device: CPU0 (slip_open) CPU1 (slip_close) unregister_netdev() rtnl_unlock() netdev_run_todo() __rtnl_unlock() rtnl_lock() sl_sync() dev = slip_devs[i] priv_destructor(dev) slip_devs[i] = NULL kobject_put(&dev->dev.kobj) /* dev is freed */ sl = netdev_priv(dev) if (sl->tty || sl->leased) /* use-after-free */ BUG: KASAN: use-after-free in sl_sync drivers/net/slip/slip.c:730 [inline] BUG: KASAN: use-after-free in slip_open+0xef4/0x1210 drivers/net/slip/slip.c:806 Read of size 1 at addr ffff8880712dac71 by task syz-executor.2/6506 CPU: 2 PID: 6506 Comm: syz-executor.2 Not tainted 6.1.134-syzkaller-00260-g0c8fc3469765 #0 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 Call Trace: sl_sync drivers/net/slip/slip.c:730 [inline] slip_open+0xef4/0x1210 drivers/net/slip/slip.c:806 tty_ldisc_open+0xa2/0x120 drivers/tty/tty_ldisc.c:433 tty_set_ldisc+0x324/0x720 drivers/tty/tty_ldisc.c:564 tiocsetd drivers/tty/tty_io.c:2428 [inline] tty_ioctl+0x5f0/0x1530 drivers/tty/tty_io.c:2712 Allocated by task 6502: alloc_netdev_mqs+0x98/0xfe0 net/core/dev.c:10719 sl_alloc drivers/net/slip/slip.c:756 [inline] slip_open+0x36d/0x1210 drivers/net/slip/slip.c:817 tty_ldisc_open+0xa2/0x120 drivers/tty/tty_ldisc.c:433 tty_set_ldisc+0x324/0x720 drivers/tty/tty_ldisc.c:564 Freed by task 6497: device_release+0xa2/0x240 drivers/base/core.c:2507 kobject_put+0x179/0x280 lib/kobject.c:729 netdev_run_todo+0x6c8/0xef0 net/core/dev.c:10509 slip_close+0x166/0x1c0 drivers/net/slip/slip.c:906 tty_ldisc_close+0x113/0x1a0 drivers/tty/tty_ldisc.c:456 tty_ldisc_kill+0x94/0x160 drivers/tty/tty_ldisc.c:614 tty_ldisc_release+0xe3/0x2b0 drivers/tty/tty_ldisc.c:782 tty_release+0xbcc/0xe70 drivers/tty/tty_io.c:1860 Commit e58c191 ("slip: Fix use-after-free Read in slip_open") fixed a different source of stale entries - a device left in slip_devs[] after slip_open() freed it on the registration error path - and does not address this race, which is why the report survives it. Drop the entry from ndo_uninit instead. unregister_netdevice() calls ndo_uninit under RTNL, before the device is queued to netdev_run_todo(), [Commit description truncated; see the upstream URL below] Changed files: drivers/net/slip/slip.c drivers/tty/tty_ldisc.c drivers/tty/tty_io.c net/core/dev.c drivers/base/core.c lib/kobject.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=a235b20972bbd98ca1fb127d6269434edc607f19 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-81001 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-81001 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:N/I:N/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: 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).