From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80857][MODERATE 7.0] fuse: wait for FR_FINISHED on abort_on_kill to prevent use-after-free Date: Fri, 04 Sep 2026 14:47:50 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80857 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: unknown X-AL-KERNEL-Commit: 715cb86e33cda43f5224cdc3fd5610c0b6a46f7a List-Id: CVE: CVE-2026-80857 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: fuse: wait for FR_FINISHED on abort_on_kill to prevent use-after-free Commit: 715cb86e33cda43f5224cdc3fd5610c0b6a46f7a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=715cb86e33cda43f5224cdc3fd5610c0b6a46f7a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80857 Analysis date: Fri, 04 Sep 2026 14:47:50 -0400 ActionableScore: 5 ActionableScore lower bound: unknown 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-2026-80857 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80857 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-2026-80857 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-80857 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: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 use-after-free can occur in the FUSE request_wait_answer abort_on_kill path because the caller can abort the connection and return without waiting for FR_FINISHED while fuse_dev_do_write is concurrently processing the same request with FR_LOCKED set. The caller may then release req args while the FUSE device write path still accesses them, which can crash the kernel and may create a memory corruption primitive depending on allocator reuse and timing. For the CVSS the PR:L is used because triggering requires local code execution with access to a FUSE mount or /dev/fuse rather than a remote network packet. The issue is not network reachable in the usual deployment model. Impact is at least local denial of service via kernel crash, and the paranoid score keeps C:H/I:H/A:H because this is an explicit UAF race that should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) SKIP CVE-2026-80857 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE WRITE OOB DANGER DISK UAF LINUS SYZBOT KPANIC KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 4 * Conservative score: 5 * Raw paranoid score: 5 * Paranoid score: 5 * Applied conservative floor/cap: Real UAF FLOOR 5 applied because this is a below-host-admin active FUSE request lifetime UAF where `fuse_dev_do_write()` may continue accessing freed `req->args`. * Applied paranoid floor/cap: none * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown Positive signals: * +2 Real UAF / active lifetime violation: `request_wait_answer()` may return after `fuse_chan_abort()` without waiting for `FR_FINISHED`, allowing `req->args` to be freed while `fuse_dev_do_write()` is still using the same request. * +1 Reliable kernel crash / strong DoS: the commit explicitly states a use-after-free, and the expected demonstrated consequence is kernel memory fault or crash. * +1 Local unprivileged trigger: FUSE is commonly reachable by local users through FUSE mounts or `/dev/fuse`, and the supplied context uses PR:L rather than host-admin-only reachability. * +1 Paranoid attacker-influenced lifetime/timing: a local FUSE actor can plausibly influence request lifetime, abort timing, and userspace device write timing. This supports unresolved exploitation review but does not prove controlled reclaim. Non-awarded signals: * +0 Controlled reclaim not demonstrated. * +0 Arbitrary or directed kernel write not demonstrated. * +0 Concrete repeated release/refcount signal not awarded. The patch shows stale access to freed `req->args`, not a second `put`, `free`, or refcount mutation on the same dangling reference. * +0 Structured stale-object leverage not separately awarded. The stale access is real, but the supplied diff does not establish attacker-shaped replacement fields, callback use, or a distinct post-reuse structured primitive. * +0 Weak LPE not separately awarded because generic UAF alone is insufficient. * +0 Extra Availability not awarded because the crash/DoS is already counted once. * +0 C/I not awarded in the arithmetic because confidentiality or integrity impact is not directly established beyond unresolved UAF exploitation potential. * +0 Remote reachability not awarded. This is not a network-triggered issue. Negative signals: * 0 No host-admin penalty. Host-admin-equivalent privilege is not positively established. * 0 No race penalty. Although the bug is concurrent, the supplied evidence does not establish a narrow one-shot race that is externally uncontrollable. * 0 No rare subsystem penalty. FUSE is a normal kernel interface and not rare hardware. Repeated-release/refcount checklist: * First release can end lifetime: not the relevant primitive here. * Exact same reference survives into second release: not established. * Second operation mutates lifetime/refcount: no. * Concrete repeated release/refcount +1 awarded: no. * Paranoid repeated-refcount leverage +1 awarded: no. * FLOOR 5 applied: yes, but due to active UAF surface below host admin, not due to repeated release. 3. Reachability analysis The evaluated attacker is a local user or local process with access to a FUSE mount or `/dev/fuse`. This is below host-admin in common FUSE deployments, so `HostAdminRequired=NO`. The issue is not namespace-scoped in the relevant sense. The supplied evidence does not depend on a namespace capability chain, so `NamespaceScopedPrivilege=NO`. No network trigger is established. The vulnerable sequence is local FUSE request handling: one path aborts on fatal signal with `abort_on_kill`, while the FUSE device write path may concurrently process the same request with `FR_LOCKED` set. No special hardware is required. No prior host-admin-only device setup is established from the supplied input. Race repeatability is plausible because a local FUSE actor can drive request creation, signal/abort behavior, and concurrent device writes, but the exact reliability of exploitation beyond crash remains unresolved. 4. Primitive and severity interpretation The exact primitive is a real use-after-free of `req->args`. The stale object is part of an active FUSE request path rather than a fixed DMA buffer or a pure destructor-only cleanup object. This is not merely an ordinary stale cleanup dereference. The stale access can occur while `fuse_dev_do_write()` is actively processing the same request. However, the patch does not establish controlled reclaim, arbitrary read/write, callback hijack, or a concrete second lifetime/refcount mutation. Primitive class is `CLASS_B`: a real kernel lifetime/corruption primitive exists, but the supplied evidence does not prove a Class A exploitation primitive. Demonstrated consequence is local kernel crash or DoS. Speculative consequence is possible memory-corruption leverage depending on allocator reuse and timing, but that is not strong enough to score as controlled LPE. `ImportantCandidate=YES` because this is an explicit below-host-admin active UAF in FUSE request processing and exploitation leverage beyond crash remains unresolved. `AutoDowngradeAllowed=NO` because automatically closing it as ordinary Moderate would discard a real unresolved kernel lifetime primitive. This does not mean proven Important, but it should receive manual review. Likely operational severity: Actionable Moderate at minimum, with Important-candidate review justified. 5. One-sentence report phrase A local FUSE user can trigger a use-after-free when the abort_on_kill path returns without waiting for FR_FINISHED while fuse_dev_do_write is still processing the same request, causing at least a kernel crash and requiring manual review for possible memory corruption impact. 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: explicit UAF race in an active local kernel interface, below-host-admin reachability is plausible, and exploitation leverage beyond crash is unresolved. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: fuse: wait for FR_FINISHED on abort_on_kill to prevent use-after-free Commit: 715cb86e33cda43f5224cdc3fd5610c0b6a46f7a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=715cb86e33cda43f5224cdc3fd5610c0b6a46f7a Commit description: The abort_on_kill path in request_wait_answer() calls fuse_abort_conn() and returns without waiting for FR_FINISHED. If fuse_dev_do_write() is concurrently processing the same request (FR_LOCKED set), the caller frees req->args while it is still being accessed, causing a use-after-free. Fix this by jumping to the existing wait_event(FR_FINISHED) instead of returning early. The wait will not hang because fuse_abort_conn() ensures all requests are ended. Reported-by: syzbot+d6540a3fa1626e11360d@syzkaller.appspotmail.com Fixes: 204aa22 ("fuse: abort on fatal signal during sync init") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-6 Signed-off-by: Rochan Avlur Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman Changed files: fs/fuse/dev.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=715cb86e33cda43f5224cdc3fd5610c0b6a46f7a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80857 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80857 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: 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).