From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53263][MODERATE REGULAR] 6lowpan: fix off-by-one in multicast context address compression [ Upstream Date: Thu, 25 Jun 2026 10:43:00 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53263 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: 3 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: f24a58c72a45f4c109f3557a760cc4b60b7a6037 List-Id: CVE: CVE-2026-53263 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: 6lowpan: fix off-by-one in multicast context address compression [ Upstream Commit: f24a58c72a45f4c109f3557a760cc4b60b7a6037 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f24a58c72a45f4c109f3557a760cc4b60b7a6037 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53263 Analysis date: Thu, 25 Jun 2026 10:43:00 -0400 ActionableScore: 3 ActionableScore lower bound: 2 Actionable bucket: Ordinary Moderate / Borderline manual review recommended Manual review required: YES Summary: An off-by-one in 6lowpan multicast context address compression leaves one byte of stack memory uninitialized and transmits it over adjacent 6lowpan traffic, causing a limited kernel information disclosure without a demonstrated crash or privilege escalation primitive. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53263 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53263 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-2026-53263 MODERATE CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N';CWE-193;CWE-908;*CWE-200;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.3';DESCR 'An off by one in lowpan_iphc_mcast_ctx_addr_compress corrupts the RIID byte and leaves data 5 uninitialized before the compressed multicast address is sent with lowpan_push_hc_data. An adjacent 6lowpan peer or sniffer may observe one byte of kernel stack data in affected multicast compression traffic. For the CVSS the PR:N because the attacker does not need local account privileges on the victim, but does need reachability to the same 6lowpan link or the ability to observe that adjacent network. The issue is not Internet routable in the usual sense and practical exposure is limited to deployments using 6lowpan stateful multicast context compression. Impact is primarily confidentiality loss from kernel stack information disclosure, with no clear crash or privilege escalation primitive from the patch alone.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Borderline manual review recommended (with actual score 3) YES OOB LEAK LINUS INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 3 * Final recommended bucket: **Ordinary Moderate / Borderline manual review recommended**:: ## 2. Signal breakdown Triggered signals: * Remote reachable / network-triggerable: +2 The leaked byte is transmitted over 6lowpan traffic via `lowpan_push_hc_data()`. This is not Internet-reachable in the usual sense, but it is observable by an adjacent 6lowpan peer or sniffer. * Confidentiality impact plausible: +1 `data[5]` is left uninitialized and then transmitted, creating a concrete kernel stack information disclosure primitive. * Rare AND difficult-to-reach subsystem/configuration: -1 6lowpan multicast context compression is a specialized low-power networking path and depends on affected runtime configuration and traffic. Paranoid-only interpretation: * Do not apply the rare-subsystem penalty: +1 relative to conservative If the affected device is deployed in an exposed 6lowpan mesh or sensor network, the adjacent-network disclosure may be operationally meaningful despite the niche subsystem. Not triggered: * Generic memory corruption: +0 The off-by-one corrupts the protocol buffer layout, but the overwrite stays within the local 6-byte stack array and does not show an OOB write into adjacent kernel memory. * Privilege escalation plausible: +0 No reclaim, overwrite, type confusion, callback, refcount, or arbitrary write primitive is shown. * Reliable kernel crash / strong DoS: +0 The patch describes information disclosure and address compression corruption, not a reliable crash. ## 3. Reachability analysis An adjacent 6lowpan participant or passive observer can potentially receive or observe the leaked byte when affected multicast context address compression is used. The attacker does not need a local account on the victim. Namespaces and containers are not the main factor because the relevant exposure is through the 6lowpan link. The path is not broadly default-exposed on ordinary Linux systems, but it is realistic for devices using 6lowpan in IoT, sensor, or low-power mesh deployments. ## 4. Severity interpretation This behaves like an ordinary Moderate issue with manual-review value, not an Important-class vulnerability. The concrete primitive is a one-byte uninitialized kernel stack disclosure over adjacent network traffic. Theoretical follow-on value exists because stack leaks can assist exploitation of other bugs, but this patch does not show memory corruption outside the local buffer, privilege escalation, or reliable DoS. ## 5. One-sentence report phrase An off-by-one in 6lowpan multicast context address compression leaves one byte of stack memory uninitialized and transmits it over adjacent 6lowpan traffic, causing a limited kernel information disclosure without a demonstrated crash or privilege escalation primitive. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This is not high scoring by itself, but it is a network-adjacent kernel stack information leak, so it should not be blindly auto-closed without confirming exposure of 6lowpan multicast context compression in the affected product. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: 6lowpan: fix off-by-one in multicast context address compression [ Upstream Commit: f24a58c72a45f4c109f3557a760cc4b60b7a6037 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f24a58c72a45f4c109f3557a760cc4b60b7a6037 Changed files: net/6lowpan/iphc.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=f24a58c72a45f4c109f3557a760cc4b60b7a6037 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53263 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53263 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:A/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N The Best / paranoid CVSS score: 5.3 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: 3 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).