From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53012][MODERATE REGULAR] nexthop: fix IPv6 route referencing IPv4 nexthop [ Upstream Date: Thu, 25 Jun 2026 14:26:41 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53012 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: ceffe81a0be92afc0cd1340bc8ca46559cce9bb4 List-Id: CVE: CVE-2026-53012 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: nexthop: fix IPv6 route referencing IPv4 nexthop [ Upstream Commit: ceffe81a0be92afc0cd1340bc8ca46559cce9bb4 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ceffe81a0be92afc0cd1340bc8ca46559cce9bb4 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53012 Analysis date: Thu, 25 Jun 2026 14:26:41 -0400 ActionableScore: 4 ActionableScore lower bound: 1 Actionable bucket: Borderline, manual review recommended Manual review required: YES Summary: A stale `has_v4` flag in nexthop groups can allow invalid IPv6 routes to reference IPv4 nexthop members, causing a NULL pointer dereference and kernel panic during IPv6 route lookup when route configuration is controlled locally or through delegated network namespaces. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53012 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53012 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-2026-53012 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-754;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference can occur in the nexthop route lookup path because a nexthop group can keep a stale has_v4 false state after an IPv6 nexthop is replaced with an IPv4 nexthop. This stale state can allow an IPv6 route to reference a group that effectively contains only IPv4 nexthop members, and a later IPv6 lookup can call nexthop_fib6_nh() and receive NULL. A local actor can trigger the crash by configuring nexthops and an IPv6 route and then causing traffic for that route. For the CVSS the PR:L is used in the paranoid score because reliable triggering requires local route or nexthop configuration rights, and on systems with user namespaces or delegated network administration this may be reachable by a non root local user with CAP_NET_ADMIN in a network namespace. The issue is not directly network reachable as a standalone remote attack because the unsafe state is created through control plane route configuration. Impact is denial of service via kernel crash, with no concrete evidence of information disclosure or privilege escalation from this NULL dereference.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3) MAYBE REMOTE DANGER NULLPTR NETWORK IPV6 SYZBOT DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=1 ## 1. ActionableScore * Conservative score: 1 * Paranoid score: 4 * Final recommended bucket: **Borderline, manual review recommended**:: ## 2. Signal breakdown Conservative signals: * Reliable kernel crash / strong DoS: +1. The commit includes a concrete reproducer ending in a panic through `nexthop_fib6_nh()` returning NULL. * Requires CAP_NET_ADMIN in typical deployments: -2. Creating and replacing nexthops and adding IPv6 routes normally requires network administration privileges. * Common networking route-management path: +1. This is in the kernel nexthop and IPv6 routing infrastructure, but the trigger is control-plane configuration, not ordinary remote packet input. * Availability impact realistic: +1. The impact is a host kernel panic after route lookup, but this mostly overlaps with the DoS signal. Paranoid additions / interpretation: * Local unprivileged trigger: +1. On systems with unprivileged user namespaces or delegated network namespaces, a local user may obtain CAP_NET_ADMIN inside a netns and exercise nexthop configuration. * CAP penalty reduced: 0 instead of -2. Namespace delegation can make this reachable below full host-root privilege. * No generic memory corruption score. This is a NULL pointer dereference from stale route state, not UAF, OOB write, double-free, or controlled overwrite. * No privilege escalation score. The patch supports crash/DoS, not an LPE primitive. ## 3. Reachability analysis The direct trigger is local route-control configuration: create an IPv6 nexthop, create a group, replace the nexthop with IPv4, attach an IPv6 route to the stale group, then trigger lookup. In ordinary host deployments this requires CAP_NET_ADMIN, so the conservative score is low. The more actionable case is namespace-dependent. If unprivileged users can create user and network namespaces, or if containers receive CAP_NET_ADMIN in their own netns, the same kernel code path may become reachable by a non-root local actor and still crash the host kernel. The bug is not remotely network-triggerable by packet traffic alone because the invalid state must first be created through nexthop and route configuration. ## 4. Severity interpretation This behaves like a local or namespace-reachable DoS, not an Important-class memory corruption issue. The demonstrated primitive is a NULL pointer dereference caused by stale nexthop group bookkeeping. There is no evidence of UAF reclaim, arbitrary write, object confusion, data disclosure, or privilege escalation. Because the crash is reliable and the PR level depends on namespace policy, it should not be treated as a trivial auto-close in environments allowing unprivileged netns usage. It is best classified as Borderline / actionable Moderate for manual triage, not a Strong Important candidate. ## 5. One-sentence report phrase A stale `has_v4` flag in nexthop groups can allow invalid IPv6 routes to reference IPv4 nexthop members, causing a NULL pointer dereference and kernel panic during IPv6 route lookup when route configuration is controlled locally or through delegated network namespaces. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Manual review is recommended because exploitability depends heavily on namespace and CAP_NET_ADMIN exposure. The issue is likely DoS-only, but systems with unprivileged user namespaces or delegated container networking may make the trigger reachable by non-root local users. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: nexthop: fix IPv6 route referencing IPv4 nexthop [ Upstream Commit: ceffe81a0be92afc0cd1340bc8ca46559cce9bb4 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ceffe81a0be92afc0cd1340bc8ca46559cce9bb4 Changed files: net/ipv4/nexthop.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=ceffe81a0be92afc0cd1340bc8ca46559cce9bb4 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53012 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53012 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:L/PR:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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).