From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-68297][MODERATE REGULAR] tipc: fix u16 MTU truncation in media and bearer MTU validation [ Upstream Date: Mon, 10 Aug 2026 11:26:09 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-68297 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: 3 X-AL-KERNEL-Commit: f02334a9e378f7e07232b26dc3d2ab353339f040 List-Id: CVE: CVE-2026-68297 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: tipc: fix u16 MTU truncation in media and bearer MTU validation [ Upstream Commit: f02334a9e378f7e07232b26dc3d2ab353339f040 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f02334a9e378f7e07232b26dc3d2ab353339f040 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68297 Analysis date: Mon, 10 Aug 2026 11:26:09 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline Moderate. Manual review recommended Manual review required: YES Summary: TIPC netlink MTU validation allowed values above U16_MAX to truncate into u16 link MTU fields, allowing a local unprivileged user via user namespace to trigger division by zero and crash the kernel. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68297 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68297 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-2026-68297 MODERATE CHECK WITH IMPACT FROM ORIG NN IMPORTANT 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-190;CWE-681;CWE-369;*CWE-20;BEST CVSS score: '5.5';DESCR 'TIPC netlink MTU validation accepted user supplied values above U16_MAX and later stored them in u16 MTU fields. A value such as 65536 can truncate to 0 and reach queue limit calculation, causing a division by zero and a kernel crash. For the CVSS the PR:L is used because reliable triggering requires local code execution and TIPC netlink configuration, although this may be possible for an unprivileged user through a user namespace. The issue is not a remote packet only attack because packet receive paths appear after the local control plane state has been configured. Impact is denial of service via kernel crash. No concrete UAF, OOB write, arbitrary write, or information leak primitive is indicated by the code change, so confidentiality and integrity are not scored.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate. Manual review recommended (with actual score 4) YES DANGER TIPC IMPROVEONLY LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 4 * Final recommended bucket: **Borderline Moderate. Manual review recommended**:: ## 2. Signal breakdown Triggered signals: * Local unprivileged trigger: +1 The report states the crash was triggered as an unprivileged user via user namespace. * Reliable kernel crash / strong DoS: +1 MTU value 65536 truncates to 0 in u16 fields and reaches division by zero in tipc_link_set_queue_limits(). * Availability impact realistic: +1 The result is a host kernel crash, not only a warning or local process failure. Paranoid-only signal: * Cross-boundary isolation/policy bypass: +1 If an unprivileged user namespace can configure the TIPC netlink state and crash the host kernel, this crosses the expected namespace containment boundary. Not triggered: * Remote reachable / network-triggerable: +0 The UDP receive stack appears in the crash path, but reliable triggering depends on prior local TIPC netlink configuration. * Generic memory corruption: +0 The patch shows integer truncation and division by zero, not UAF, OOB write, double free, type confusion, or arbitrary write. * Privilege escalation plausible: +0 No concrete memory corruption or privilege-changing primitive is indicated. * High-control kernel data-plane API: +0 This is netlink control-plane configuration, not a rich unprivileged data-plane shaping primitive. Call-site confidence: high. The input includes the crash stack and the affected downstream path from netlink MTU setting to link creation and division by zero. ## 3. Reachability analysis A local user can potentially trigger the bug if unprivileged user namespaces are enabled and allow creation of a context where TIPC media or bearer MTU configuration is reachable. In deployments where user namespaces are disabled or TIPC configuration requires host CAP_NET_ADMIN, the practical score would be lower. The bug is not a pure remote packet parser issue because the dangerous state is created through local netlink configuration before the receive path reaches the crash. TIPC is not universally enabled or commonly exposed on default systems, but the reported unprivileged user namespace trigger makes this more actionable than an ordinary privileged-only configuration bug. ## 4. Severity interpretation This behaves like an actionable local DoS, not an Important-class memory corruption issue. The practical impact is a kernel crash caused by integer truncation and division by zero. There is no demonstrated confidentiality impact, integrity impact, UAF reclaim, overwrite, object confusion, or privilege escalation path. The paranoid score is higher only because the trigger may cross a namespace boundary from an unprivileged user context to a host-wide kernel crash. ## 5. One-sentence report phrase TIPC netlink MTU validation allowed values above U16_MAX to truncate into u16 link MTU fields, allowing a local unprivileged user via user namespace to trigger division by zero and crash the kernel. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: the bug is DoS-only based on the patch, but the reported unprivileged user namespace trigger and host-wide networking subsystem crash make it unsuitable for automatic low-priority closure. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: tipc: fix u16 MTU truncation in media and bearer MTU validation [ Upstream Commit: f02334a9e378f7e07232b26dc3d2ab353339f040 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f02334a9e378f7e07232b26dc3d2ab353339f040 Changed files: net/tipc/link.c net/tipc/node.c net/tipc/discover.c net/tipc/udp_media.c net/tipc/netlink.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=f02334a9e378f7e07232b26dc3d2ab353339f040 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68297 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68297 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: Not available 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: 3 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).