From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80996][LOW] net: l2tp: do not propagate multicast notification errors Date: Fri, 11 Sep 2026 17:33:15 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80996 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: 1 X-AL-KERNEL-Commit: 0fe037d5eaad938aa3e9143ee071aa237750b42b List-Id: CVE: CVE-2026-80996 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: net: l2tp: do not propagate multicast notification errors Commit: 0fe037d5eaad938aa3e9143ee071aa237750b42b Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0fe037d5eaad938aa3e9143ee071aa237750b42b Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80996 Analysis date: Fri, 11 Sep 2026 17:33:15 -0400 ActionableScore: 2 ActionableScore lower bound: 1 Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80996 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80996 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-2026-80996 LOW https://www.kernelcve.org/list/?q=CVE-2026-80996 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-703;CWE-755;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'L2TP netlink create and modify handlers could return a multicast notification error after the live tunnel or session operation had already completed. This creates a state mismatch where user space may believe the operation failed and retry it, while the kernel object already exists. Repeated retries can accumulate live L2TP tunnels or sessions and may lead to resource exhaustion. For the CVSS the PR:L is used because triggering requires local access to the L2TP generic netlink control plane with CAP_NET_ADMIN or an equivalent delegated network administration capability. The issue is not directly network reachable and is triggered by local control plane commands rather than L2TP packet traffic. Impact is denial of service through resource consumption only.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES SIMPLEFIX LINUS NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ActionableScoreLower=1 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate**:: No floor or cap changed the score. 2. Signal breakdown Conservative signals: * +1: committed-operation state mismatch. L2TP create or modify can succeed, but the command may return a multicast notification error afterward, causing callers to retry while the kernel object already exists. * +1: resource accumulation concern. Repeated retries may accumulate live L2TP tunnels or sessions. * -1: privilege-gated local control plane. Triggering requires access to L2TP generic netlink create or modify operations, normally requiring CAP_NET_ADMIN or equivalent delegated network administration rights. Paranoid delta: * +1: sustained retries may produce stronger resource exhaustion than a single failed command result. Non-awarded signals: * RealUAF not awarded. No stale pointer, post-free dereference, double release, or refcount corruption is shown. * PrimitiveClass remains NONE. The patch shows error propagation semantics, not kernel memory corruption. * Controlled reclaim not demonstrated. * Arbitrary write not demonstrated. * Confidentiality and integrity impact not awarded. * Remote reachability not awarded because the issue is triggered through local netlink control plane commands, not L2TP packet traffic. * Concrete persistent kernel reference leak not awarded because objects are live and intentionally committed, not lost references from kernel cleanup. * Reliable kernel crash not awarded because the demonstrated consequence is possible resource accumulation, not panic or Oops. * Extra availability point beyond resource exhaustion not awarded. 3. Reachability analysis The vulnerable path is reached by issuing L2TP tunnel or session create or modify commands through generic netlink. The multicast notification is sent after the live operation has already completed. If notification allocation, encoding, or multicast delivery fails, the old code returned that notification error as the command result. The attacker is a local control-plane actor, not a remote packet sender. Ordinary network traffic does not directly trigger the bug. The relevant privilege is expected to be CAP_NET_ADMIN or equivalent rights for the target network context. The supplied evidence does not fully prove whether the complete trigger chain is available with attacker-created namespaces, so NamespaceScopedPrivilege is UNKNOWN. HostAdminRequired is also UNKNOWN because host-admin-equivalent privilege is not positively established, but below-host-admin namespace reachability is not fully established either. No special hardware, firmware, boot mode, or race timing is required. The effect depends on callers retrying after a false failure and on notification failure conditions. 4. Primitive and severity interpretation The exact primitive is a logic and error-handling flaw: best-effort multicast notification failure is reported as failure for an already committed L2TP operation. This can produce user/kernel state disagreement and repeated creation of live objects. This is not active structured UAF, not fixed stale storage, and not cleanup lifetime corruption. No concrete repeated release or refcount mutation exists. The first operation does not free an object and no second lifetime operation on a dangling reference is shown. PrimitiveClass is NONE because the patch establishes no memory corruption, lifetime violation, authorization bypass, semantic reinterpretation, or ownership violation. The demonstrated consequence is resource consumption from retries. The speculative stronger consequence is broader resource exhaustion under sustained abuse, but there is no evidence of privilege escalation or confidentiality/integrity impact. ImportantCandidate is NO because the issue is DoS/resource-exhaustion oriented and lacks an unresolved corruption or boundary-bypass primitive. AutoDowngradeAllowed is YES because no meaningful Important-grade primitive would be lost by treating this as ordinary Moderate or Low-like triage. 5. One-sentence report phrase L2TP netlink create and modify handlers could report failure after a live operation had already completed, causing callers to retry and potentially accumulate live tunnel or session objects until resources are exhausted. 6. Manual review recommendation NO MANUAL CHECK NEEDED Reason: this is a local control-plane error-handling/resource-exhaustion issue with no UAF, memory corruption, authorization bypass, remote packet trigger, or privilege-escalation evidence. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net: l2tp: do not propagate multicast notification errors Commit: 0fe037d5eaad938aa3e9143ee071aa237750b42b Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0fe037d5eaad938aa3e9143ee071aa237750b42b Commit description: The tunnel create, tunnel modify, session create, and session modify netlink handlers send multicast notifications through helpers that can fail while allocating or encoding a message, or while multicasting it. For tunnel and session create/modify, a notification is sent after the live operation has completed. Returning a best-effort notification error as the command result can therefore report failure for an operation that already committed and can cause callers to retry and accumulate live objects. Keep sending notifications for listener visibility, but do not propagate their best-effort status as the command result. This also keeps the tunnel modify command consistent with the other notification-only paths. Fixes: 33f72e6 ("l2tp : multicast notification to the registered listeners") Cc: stable@vger.kernel.org Reported-by: Vega Signed-off-by: Zihan Xi Reviewed-by: Simon Horman Link: https://patch.msgid.link/54f48e812ca0424c47ffdb9a8182180921f7e6b2.1787247008.git.zihanx@nebusec.ai Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/l2tp/l2tp_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=0fe037d5eaad938aa3e9143ee071aa237750b42b ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80996 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80996 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:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.7 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: 1 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).