From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-52927][MODERATE 7.0] netfilter: ebtables: fix OOB read in compat_mtw_from_user [ Upstream Date: Wed, 24 Jun 2026 03:52:05 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-52927 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: d7a8fb6f10d55a1c37b0bf8c20cca24dffd76e00 List-Id: CVE: CVE-2026-52927 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: netfilter: ebtables: fix OOB read in compat_mtw_from_user [ Upstream Commit: d7a8fb6f10d55a1c37b0bf8c20cca24dffd76e00 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d7a8fb6f10d55a1c37b0bf8c20cca24dffd76e00 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52927 Analysis date: Wed, 24 Jun 2026 03:52:05 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: An OOB read in ebtables compat_mtw_from_user allows a local CAP_NET_ADMIN capable process, possibly inside a delegated network namespace, to provide undersized compat match or target data and trigger invalid kernel reads during extension conversion. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-52927 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52927 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-2026-52927 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:L/I:L/A:H';CWE-125;*CWE-20;CWE-1284;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.6';DESCR 'An out of bounds read exists in the ebtables compat conversion path because compat_mtw_from_user can accept a user supplied match or target size that is smaller than the extension compatsize. Extensions that use compat_from_user may then read beyond the provided compat data while converting 32 bit ebtables structures into native kernel structures. For the CVSS the PR:L is used for the paranoid score because triggering requires a local process with CAP_NET_ADMIN or equivalent delegated network administration rights rather than full host root in all deployments. The issue is not directly network reachable and is triggered through local firewall rule update operations. Impact is at least a local denial of service via kernel crash or KASAN detected OOB read. In the worst defensible case it may allow limited confidentiality or integrity impact because the bug class is an OOB read in kernel parsing logic, but no arbitrary write primitive is shown.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) YES KASAN OOB NETFILTER IMPROVEONLY LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO guess ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 5 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown Paranoid score signals: * Local unprivileged trigger: +1. In typical host setups ebtables rule updates require CAP_NET_ADMIN, but user and network namespace delegation may make this reachable by an otherwise unprivileged local user on some systems. * Weak or indirect corruption candidate: +1. The concrete primitive is an out-of-bounds read in kernel compat parsing, not an OOB write or UAF. * Reliable kernel crash / strong DoS: +1. The commit states KASAN reports an OOB read, and malformed compat sizes can drive extension callbacks into invalid reads. * Confidentiality impact plausible: +1. OOB read in kernel parsing can theoretically expose adjacent kernel data depending on callback behavior, although no direct disclosure path is shown. * Broad/default/common subsystem exposure: +1. netfilter/ebtables is a common kernel firewall subsystem, even though this is a local compat control-plane path rather than packet receive processing. Conservative score uses the same core issue but treats CAP_NET_ADMIN as a real deployment constraint and does not assume a practical disclosure path. ## 3. Reachability analysis The bug is triggered through the ebtables compat path when converting 32-bit user supplied match, watcher, or target structures into native kernel structures. A local process must be able to submit ebtables rules, normally requiring CAP_NET_ADMIN. In containerized or namespace-enabled environments, CAP_NET_ADMIN may be delegated inside a network namespace, so the attacker may not need full host root. The issue is not remotely network-triggerable through packet traffic. Realistic exploitation requires access to the local firewall rule update interface and an extension path that uses compat_from_user and assumes compatsize bytes are readable. ## 4. Severity interpretation This behaves more like an actionable Moderate than an ordinary low-risk validation bug. The demonstrated primitive is an OOB read, so it should not be upgraded to strong memory corruption, arbitrary write, or clear LPE. Realistic impact is local DoS through a kernel fault or KASAN-detected invalid read. The paranoid score is higher because this is a kernel parser OOB read in a common netfilter subsystem with possible namespace-based reachability and limited confidentiality concern, but the patch does not show a strong privilege escalation primitive. ## 5. One-sentence report phrase An OOB read in ebtables compat_mtw_from_user allows a local CAP_NET_ADMIN capable process, possibly inside a delegated network namespace, to provide undersized compat match or target data and trigger invalid kernel reads during extension conversion. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This should not be auto-closed because it is a kernel OOB read in a netfilter parser path with namespace-dependent privilege requirements and possible limited confidentiality impact, even though the realistic baseline impact is DoS rather than proven privilege escalation. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: netfilter: ebtables: fix OOB read in compat_mtw_from_user [ Upstream Commit: d7a8fb6f10d55a1c37b0bf8c20cca24dffd76e00 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d7a8fb6f10d55a1c37b0bf8c20cca24dffd76e00 Changed files: net/bridge/netfilter/ebtables.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=d7a8fb6f10d55a1c37b0bf8c20cca24dffd76e00 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-52927 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52927 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:L/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:L/I:L/A:H The Best / paranoid CVSS score: 6.6 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).