From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53013][LOW] macvlan: fix macvlan_get_size() not reserving space for IFLA_MACVLAN_BC_CUTOFF [ Upstream Date: Wed, 24 Jun 2026 12:51:12 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53013 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: 0 X-AL-KERNEL-Commit: 4979252758387b338ca968ba7e0515b0ae2257e3 List-Id: CVE: CVE-2026-53013 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: macvlan: fix macvlan_get_size() not reserving space for IFLA_MACVLAN_BC_CUTOFF [ Upstream Commit: 4979252758387b338ca968ba7e0515b0ae2257e3 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4979252758387b338ca968ba7e0515b0ae2257e3 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53013 Analysis date: Wed, 24 Jun 2026 12:51:12 -0400 ActionableScore: 2 ActionableScore lower bound: 0 Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: macvlan_get_size() failed to reserve space for IFLA_MACVLAN_BC_CUTOFF, causing rtnetlink dumps to fail with EMSGSIZE and trigger a warning for affected local macvlan configurations, with impact limited to local control-plane denial of service. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53013 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53013 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: LOW 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-2026-53013 LOW 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-131;CWE-617;CWE-755;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'macvlan_get_size() failed to reserve space for the IFLA_MACVLAN_BC_CUTOFF netlink attribute while macvlan_fill_info() could still emit that attribute for a configured macvlan device. This can make nla_put_s32() fail with EMSGSIZE during rtnetlink dump and can trigger a kernel warning while preventing the interface from being dumped. For the CVSS the PR:L is used in the paranoid score only for environments where a less privileged container root or delegated network administrator can create or modify macvlan devices with CAP_NET_ADMIN. The issue is local control plane only and is not network reachable through packet traffic. Impact is mainly denial of service for interface introspection and warning based availability impact. There is no evidence of memory corruption, information disclosure, or privilege escalation because the netlink write fails safely when the skb is too small.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1) YES NETWORK SKB LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO guess ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=0 ## 1. ActionableScore * Conservative score: 0 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like**:: ## 2. Signal breakdown Conservative signals: * Requires admin or CAP_NET_ADMIN in typical deployments: -2. Creating and configuring a macvlan device and setting `bc_cutoff` normally requires network administration privileges. * WARN_ON continuation only: +0. The failure is `-EMSGSIZE` from `nla_put_s32()` and a rtnetlink warning. The patch does not show memory corruption, OOB write, UAF, stale pointer reuse, or arbitrary write. * Availability impact realistic but limited: +1 could be considered, because the interface dump fails. However this is limited to control-plane introspection and not a host-wide crash in normal configurations. Paranoid signals: * Availability impact limited: +1. The interface dump can be reliably prevented for the affected macvlan configuration. * Warning based DoS concern: +1. On systems with `panic_on_warn`, the WARN_ON path could become a stronger availability issue. * Delegated CAP_NET_ADMIN caveat: no full -2 penalty in the paranoid interpretation if a container root or delegated network administrator can configure macvlan devices in a network namespace. Not applied: * No remote/network-triggerable packet path. * No generic memory corruption. * No lifetime corruption. * No confidentiality or integrity primitive. * No privilege escalation plausibility. * No high-control kernel data-plane API bonus, because this is a netlink size accounting bug with safe failure, not attacker-controlled memory lifetime or layout manipulation. ## 3. Reachability analysis The bug is triggered locally through rtnetlink control-plane operations after configuring a macvlan device with `bc_cutoff != 1`. In normal host deployments this requires `CAP_NET_ADMIN`, so an ordinary unprivileged user cannot reliably trigger it. In containerized or delegated network-administration setups, a less privileged actor with network namespace administration rights may be able to reach the path, but this still remains a local configuration path rather than packet-processing exposure. The affected feature is not a default remote attack surface. ## 4. Severity interpretation This behaves like a Low-like or ordinary Moderate issue, not an Important-class vulnerability. The technical failure is an undersized netlink skb caused by a missing `nla_total_size(4)` reservation. The write helper fails safely with `-EMSGSIZE`, causing a warning and failed interface dump. There is no realistic evidence of memory corruption, information disclosure, privilege escalation, or persistent system-wide impact. ## 5. One-sentence report phrase macvlan_get_size() failed to reserve space for IFLA_MACVLAN_BC_CUTOFF, causing rtnetlink dumps to fail with EMSGSIZE and trigger a warning for affected local macvlan configurations, with impact limited to local control-plane denial of service. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED The issue is a bounded size-accounting bug with safe netlink failure semantics, normally requiring CAP_NET_ADMIN and showing no memory corruption or privilege-boundary bypass. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: macvlan: fix macvlan_get_size() not reserving space for IFLA_MACVLAN_BC_CUTOFF [ Upstream Commit: 4979252758387b338ca968ba7e0515b0ae2257e3 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4979252758387b338ca968ba7e0515b0ae2257e3 Changed files: drivers/net/macvlan.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=4979252758387b338ca968ba7e0515b0ae2257e3 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53013 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53013 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:L 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: 0 Paranoid ActionableScore: 2 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).