From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64579][MODERATE 7.0] xfrm: policy: preallocate inexact bins before xfrm_hash_rebuild reinsert [ Upstream Date: Wed, 05 Aug 2026 05:17:43 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64579 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: d9d9cc21cc90014724a14c447e3d587be9447107 List-Id: CVE: CVE-2026-64579 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: xfrm: policy: preallocate inexact bins before xfrm_hash_rebuild reinsert [ Upstream Commit: d9d9cc21cc90014724a14c447e3d587be9447107 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d9d9cc21cc90014724a14c447e3d587be9447107 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64579 Analysis date: Wed, 05 Aug 2026 05:17:43 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: An inverted preallocation guard in `xfrm_hash_rebuild()` can leave a poisoned XFRM policy list node after allocation failure, causing a later rebuild to dereference `LIST_POISON2` and panic the kernel. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64579 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64579 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-2026-64579 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-670;CWE-703;**CWE-476;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'An inverted guard in xfrm_hash_rebuild causes preallocation to cover exact XFRM policies while skipping inexact policies that may need a bin during the reinsert phase. If allocation later fails under memory pressure after hlist_del_rcu, the error path can leave a poisoned bydst list node and a later rebuild may dereference LIST_POISON2, causing a general protection fault and kernel panic. For the CVSS the PR:L is used for the paranoid score because reliable triggering requires local ability to create or modify XFRM policies, often CAP_NET_ADMIN or delegated network administration in a namespace. The issue is not directly network reachable through packet traffic and is triggered through the XFRM control plane. Impact is at least local denial of service via kernel crash and in worst case may allow limited confidentiality or integrity impact due to corrupted list state, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) YES KASAN OOB ERRORPATH KERNEL_PANIC_PLUS_UAF LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Weak/indirect corruption candidate: +1. The failed reinsert can leave a poisoned `bydst` list node, later dereferenced through `hlist_del_rcu()`. * Real lifetime/list corruption: +1. The bug creates stale or invalid list state across rebuilds after an object was removed from the hash/list path. * Reliable kernel crash / strong DoS: +1. The commit provides a concrete GPF and kernel panic trace. * Availability impact realistic: +1. The failure is host-wide once triggered, not merely a local process crash. * Broad networking subsystem exposure: +1. XFRM/IPsec policy handling is a core networking subsystem, although not ordinary packet-path parsing. * Requires CAP_NET_ADMIN or equivalent in typical deployments: -1. Full -2 is softened because CAP_NET_ADMIN can be delegated to containers or network namespaces. * Memory pressure / special allocation failure condition: -1. The crash requires allocation failure during rebuild, although it is deterministic with failslab. Paranoid additions: * Local delegated low-privilege trigger concern: +1. In environments with unprivileged user namespaces or delegated net administration, an attacker may obtain practical control over XFRM policy creation without full host root. * Confidentiality impact plausible: +1. Limited C impact is defensible only as a manual-review concern from corrupted kernel list state, not as a proven leak. * Integrity impact plausible: +1. Limited I impact is defensible only as a corruption concern, not as a demonstrated write primitive. * No strong LPE bonus. There is no demonstrated controlled reclaim, arbitrary write, callback control, or type confusion. ## 3. Reachability analysis The bug is triggered through the XFRM policy control plane, not directly by network packets. In normal host deployments, creating or modifying relevant XFRM policies requires `CAP_NET_ADMIN`, so a fully unprivileged local user usually cannot trigger it directly. Namespaces matter. If a container, service, or user namespace setup grants effective network administration rights, the practical privilege level can drop from host-admin to lower-privileged delegated control. The issue is not remotely reachable over the network by packet traffic alone. Realistic exploitation needs inexact XFRM policies, a hash rebuild, and allocation failure under memory pressure. The commit states that the crash is deterministic with failslab, but real-world reliability depends on the attacker’s ability to shape memory pressure and policy state. ## 4. Severity interpretation This is stronger than an ordinary Moderate cleanup because the patch fixes a concrete corrupted list-state path ending in a kernel panic. It is not a Strong Important candidate on the available evidence because the primitive is a poisoned-list dereference and crash, not a controlled UAF reclaim, overwrite, type confusion, or demonstrated privilege escalation path. The conservative interpretation is local privileged DoS. The paranoid interpretation is Actionable Moderate because delegated `CAP_NET_ADMIN`, corrupted kernel list state, and a concrete panic path justify manual review. ## 5. One-sentence report phrase An inverted preallocation guard in `xfrm_hash_rebuild()` can leave a poisoned XFRM policy list node after allocation failure, causing a later rebuild to dereference `LIST_POISON2` and panic the kernel. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the issue involves corrupted kernel list state and a concrete panic path in XFRM policy rebuild logic. No proven LPE primitive is shown, but the combination of list corruption, delegated namespace reachability, and kernel panic makes auto-closure inappropriate. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: xfrm: policy: preallocate inexact bins before xfrm_hash_rebuild reinsert [ Upstream Commit: d9d9cc21cc90014724a14c447e3d587be9447107 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d9d9cc21cc90014724a14c447e3d587be9447107 Changed files: include/linux/rculist.h net/xfrm/xfrm_policy.c kernel/workqueue.c kernel/kthread.c arch/x86/kernel/process.c arch/x86/entry/entry_64.S 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=d9d9cc21cc90014724a14c447e3d587be9447107 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64579 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64579 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: 3 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: NO 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).