From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74599][MODERATE REGULAR] mm/ptdump: always stabilise against page table freeing using init_mm Date: Sat, 22 Aug 2026 12:06:31 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74599 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: 4 X-AL-KERNEL-ActionableScore-Lower: 1 X-AL-KERNEL-Commit: 7f740664aec1f832953c2e6d9b8920cd6c8bcc0c List-Id: CVE: CVE-2026-74599 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: mm/ptdump: always stabilise against page table freeing using init_mm Commit: 7f740664aec1f832953c2e6d9b8920cd6c8bcc0c Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7f740664aec1f832953c2e6d9b8920cd6c8bcc0c Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74599 Analysis date: Sat, 22 Aug 2026 12:06:31 -0400 ActionableScore: 4 ActionableScore lower bound: 1 Actionable bucket: Borderline manual review recommended / not Strong Important on current evidence Manual review required: YES Summary: ptdump can race with kernel page table freeing when dumping kernel mappings through a non init_mm mm, creating a local page-table lifetime UAF candidate that is most likely to cause a kernel crash but deserves manual review due to the sensitivity of page-table state. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74599 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74599 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74599 MODERATE 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:L/I:L/A:H';CWE-362;*CWE-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'ptdump can race with kernel page table freeing when it walks kernel mappings through an mm other than init_mm. Kernel page table ranges are shared across mm objects, so locking only the walked mm may not stabilize the kernel page tables that are being dumped. The likely impact is a local denial of service through a kernel crash or inconsistent page table traversal. For the CVSS the PR:L reflects a conservative review case where ptdump or related debug access is delegated to a reduced capability root, container root, or service account rather than full host admin. The issue is not network reachable and requires local access to a ptdump capable debug 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 a page table use after free candidate and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / not Strong Important on current evidence (with actual score 3) YES READ LOCK DEADLOCK DANGER NULLPTR INIT RACE IMPROVEONLY MEMORY DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=1 ## 1. ActionableScore * Conservative score: 1 * Paranoid score: 4 * Final recommended bucket: **Borderline manual review recommended / not Strong Important on current evidence**:: ## 2. Signal breakdown Conservative signals: * Weak or indirect corruption candidate: +1. ptdump can walk kernel page tables while they are being freed, so stale page-table memory may be read or interpreted during traversal. * Real lifetime corruption: +1. The patch explicitly fixes a race with page table freeing by adding init_mm locking. * Reliable kernel crash / strong DoS: +1. The realistic failure mode is an invalid page-table walk, crash, WARN, or inconsistent traversal. * Hard or unreliable race / special timing required: -1. Triggering requires a timing window between ptdump traversal and kernel page table freeing. * Requires admin/root/CAP-like debug access in typical deployments: -2. ptdump is normally exposed through privileged debug interfaces, commonly debugfs. Paranoid additional interpretation: * Weak LPE concern: +1. Because the stale object is page-table memory, reused freed memory could theoretically be interpreted as paging structures, but the patch does not show a write primitive, callback control, or attacker-controlled reclaim. * Reduced-privilege access model considered: no -2 penalty in paranoid score. If ptdump access is delegated to reduced-capability root, container root, a service account, or a debugging service, it is not equivalent to full host-root in practical risk terms. * No remote/network signal. The affected path is local debug/control-plane functionality, not packet processing. * No strong corruption primitive. There is no demonstrated arbitrary write, OOB write, type confusion with controlled replacement, or page-cache/COW ownership bypass. Call-site confidence: high. The relevant callers and locking context are present in the supplied patch. ## 3. Reachability analysis The bug is triggerable by a local actor who can invoke ptdump on x86 or arm64 over an mm other than init_mm while kernel page tables are concurrently freed. In typical production deployments this requires privileged debug access, so the conservative score is low. Namespaces or containers matter only if a product delegates ptdump or equivalent debug access to a reduced-privilege context. The path is not remotely reachable and is not triggered by ordinary network traffic. Realistic exploitation is mainly a local crash or unstable page-table traversal rather than a demonstrated privilege escalation. ## 4. Severity interpretation This behaves more like a borderline manual-review Moderate than an Important-class issue on the evidence provided. The theoretical concern is a race-dependent page-table UAF candidate, which is more sensitive than a simple NULL dereference because page-table memory is security-critical. The realistic evidence still points mostly to local DoS, with no demonstrated attacker-controlled reclaim, write-after-free, arbitrary write, or reliable privilege-escalation primitive. ## 5. One-sentence report phrase ptdump can race with kernel page table freeing when dumping kernel mappings through a non init_mm mm, creating a local page-table lifetime UAF candidate that is most likely to cause a kernel crash but deserves manual review due to the sensitivity of page-table state. ## 6. Manual review recommendation MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK because this is a race against page table freeing and a UAF candidate in core mm page-table traversal, even though the currently supported practical impact is mainly local DoS. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: mm/ptdump: always stabilise against page table freeing using init_mm Commit: 7f740664aec1f832953c2e6d9b8920cd6c8bcc0c Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7f740664aec1f832953c2e6d9b8920cd6c8bcc0c Commit description: Previous commits have established the invariant that kernel page table freeing is performed while an mmap read lock on init_mm is held, which fixes races between ptdump and kernel page table freeing over init_mm. However, x86 and arm64 can perform a ptdump over an mm other than init_mm via ptdump_walk_pgd() and since kernel memory ranges are shared across non-kernel mm's, this means that the race still exists for these cases. Fix this by acquiring a nested mmap write lock for init_mm in ptdump_walk_pgd(). This is safe as we take this after mmap write locking the mm, and nothing acquires the init_mm lock first before locking an arbitrary mm, so no deadlock is possible. Also update walk_page_range_debug() to assert that init_mm is write locked, add a comment explaining why and remove some redundant code, and eliminate the unnecessary and confusing invocation of walk_kernel_page_table_range(). We can safely remove the non-NULL check for walk.mm, as the mmap lock asserts would NULL pointer deref if it was (and of course no callers do this). The first point at which ptdump can race kernel page table freeing is commit b6bdb75 ("mm/vmalloc: add interfaces to free unmapped page table"), so we target this in the Fixes tag. Link: https://lore.kernel.org/20260723-series-vmap-race-fix-v6-4-8cc77dcc0018@kernel.org Fixes: b6bdb75 ("mm/vmalloc: add interfaces to free unmapped page table") Signed-off-by: Lorenzo Stoakes (ARM) Reviewed-by: Mike Rapoport (Microsoft) Acked-by: David Hildenbrand (Arm) Reviewed-by: Kiryl Shutsemau Cc: Andy Lutomirski Cc: "Borah, Chaitanya Kumar" Cc: "Borislav Petkov (AMD)" Cc: Catalin Marinas Cc: Dave Hansen Cc: David Carlier Cc: Dev Jain Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: Liam R. Howlett Cc: Michal Hocko Cc: Peter Zijlstra Cc: Ryan Roberts Cc: Shakeel Butt Cc: Suren Baghdasaryan Cc: Toshi Kani Cc: "Uladzislau Rezki (Sony)" Cc: Vlastimil Babka Cc: Will Deacon Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman Changed files: mm/pagewalk.c mm/ptdump.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=7f740664aec1f832953c2e6d9b8920cd6c8bcc0c ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74599 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74599 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: 1 Paranoid ActionableScore: 4 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).