From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-52981][MODERATE 7.0] neigh: let neigh_xmit take skb ownership [ Upstream Date: Fri, 26 Jun 2026 08:04:38 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-52981 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: 2 X-AL-KERNEL-Commit: 8a89054a1ec0767aec25ed2bbac933da6ba3cf5a List-Id: CVE: CVE-2026-52981 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: neigh: let neigh_xmit take skb ownership [ Upstream Commit: 8a89054a1ec0767aec25ed2bbac933da6ba3cf5a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8a89054a1ec0767aec25ed2bbac933da6ba3cf5a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52981 Analysis date: Fri, 26 Jun 2026 08:04:38 -0400 ActionableScore: 5 ActionableScore lower bound: 2 Actionable bucket: Actionable Moderate at minimum Manual review required: NO Summary: `neigh_xmit() could leak SKBs when called with an uninitialized neighbor table, allowing repeated packet or forwarding path triggers to cause memory exhaustion and denial of service under specific network configurations.` ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-52981 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52981 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-52981 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.8';DESCR 'neigh_xmit() could return without transmitting or freeing the SKB when the requested neighbor table is not initialized, for example NEIGH_ND_TABLE when IPv6 support is disabled. Callers historically rely on neigh_xmit() to consume SKB ownership, so ignoring the return value can turn this path into an SKB memory leak. Repeated triggering may cause resource exhaustion and denial of service, but the patch context does not indicate UAF, OOB access, information disclosure, or privilege escalation. For the CVSS the PR:L in the paranoid score reflects a scenario where a local low privileged actor can influence packet generation or a delegated network context after the vulnerable forwarding path already exists. The issue may also be packet driven in specific configurations, but reliable exploitation depends on a missing neighbor table and a caller path that reaches neigh_xmit() with such an index.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) MAYBE REMOTE LOCK SIMPLEFIX LEAK ERRORPATH SKB IPV6 INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown Paranoid score signals: * Remote reachable / network-triggerable: +2 If a vulnerable caller path is reachable from packet forwarding, repeated packets may trigger the SKB leak after the system is configured into the affected state. * Reliable kernel crash / strong DoS: +1 The bug is an SKB ownership leak. Repeated triggering can plausibly exhaust kernel networking memory and cause denial of service. * Availability impact realistic: +1 Sustained SKB leaks can produce system-wide memory pressure or networking failure. * Common networking core path or packet-processing path: +1 The affected helper is in `net/core/neighbour.c` and is used by networking transmit paths. Conservative interpretation: * Requires admin/root/CAP_NET_ADMIN in typical deployments: -2 Reliable exposure likely depends on network configuration such as MPLS or a caller path using a neighbor table index that is not initialized. * No generic memory corruption: +0 The patch fixes a missing `kfree_skb()` path. It does not indicate UAF, double-free, OOB write, object confusion, or attacker-controlled overwrite. * No confidentiality or integrity primitive: +0 The leaked object is not reused after free and no read-back or corruption sink is shown. ## 3. Reachability analysis The immediate bug is triggered when `neigh_xmit()` is called with an uninitialized neighbor table, for example `NEIGH_ND_TABLE` when IPv6 support is disabled. In that path, the old code returned without transmitting or freeing the SKB, while callers historically assumed that `neigh_xmit()` consumes SKB ownership. In typical deployments, creating the exact forwarding or encapsulation path may require administrative networking privileges such as CAP_NET_ADMIN. However, once such a path exists, the leak may be packet-driven, and a lower-privileged local user or a network-adjacent sender may be able to generate repeated traffic that exercises the path. Namespaces or delegated network administration can reduce the practical privilege requirement in containerized environments. This is not a default remote Internet exposure in the same sense as a protocol parser bug. It is a configuration-dependent networking core resource leak. ## 4. Severity interpretation This behaves more like an actionable Moderate resource-exhaustion issue than an Important memory-corruption vulnerability. The realistic impact is denial of service through SKB memory leakage. The patch does not support privilege escalation, information disclosure, UAF, or controlled memory corruption. The higher paranoid score is justified only because the affected code is in a core networking transmit helper and may be packet-driven under specific configurations. It should not be treated as a strong Important candidate unless a concrete reachable caller path is demonstrated. ## 5. One-sentence report phrase `neigh_xmit() could leak SKBs when called with an uninitialized neighbor table, allowing repeated packet or forwarding path triggers to cause memory exhaustion and denial of service under specific network configurations.` ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Manual review is recommended because this is a networking core SKB ownership bug and the practical score depends heavily on whether reachable caller paths can be packet-driven in real deployments. It is not a memory-corruption issue based on the patch alone. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: neigh: let neigh_xmit take skb ownership [ Upstream Commit: 8a89054a1ec0767aec25ed2bbac933da6ba3cf5a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8a89054a1ec0767aec25ed2bbac933da6ba3cf5a Changed files: net/core/neighbour.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=8a89054a1ec0767aec25ed2bbac933da6ba3cf5a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-52981 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52981 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:L The Best / paranoid CVSS vector: AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.8 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: 2 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).