From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-68116][MODERATE 7.0] vxlan: mdb: Fix source list corruption on a failed replace Date: Mon, 10 Aug 2026 15:47:41 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-68116 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: 5bc8fc1d2ff802eec839e03adef5df597421898d List-Id: CVE: CVE-2026-68116 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: vxlan: mdb: Fix source list corruption on a failed replace Commit: 5bc8fc1d2ff802eec839e03adef5df597421898d Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5bc8fc1d2ff802eec839e03adef5df597421898d Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68116 Analysis date: Mon, 10 Aug 2026 15:47:41 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate at minimum Manual review required: NO Summary: A failed VXLAN MDB source-list replace can corrupt the logical source state of an existing multicast remote entry, causing EXCLUDE filters to forward traffic that should be blocked or INCLUDE filters to drop traffic that should be forwarded, with typical triggering requiring CAP_NET_ADMIN or delegated network-control privileges. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68116 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68116 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-68116 MODERATE CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L';CWE-703;CWE-754;CWE-284;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:L';BEST CVSS score: '4.5';DESCR 'A failed VXLAN MDB source list replace can corrupt the logical source state of an existing (*,G) remote entry. During replace, pre existing sources are marked for deletion and new sources are added, but an error in the middle of the add path could remove old sources as well as newly created ones. With an EXCLUDE filter this can allow traffic that should be blocked to be forwarded. With an INCLUDE filter this can drop traffic that should be forwarded. For the CVSS the PR:L is used in the paranoid score because delegated CAP_NET_ADMIN, container root, or a network management service may allow a less than full host administrator to update VXLAN MDB state. The issue is not directly network reachable through VXLAN packet traffic and is triggered through control plane MDB configuration. Impact is a network forwarding policy bypass with limited confidentiality, integrity, and availability impact rather than kernel memory corruption or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) YES DANGER INIT ERRORPATH NETWORK DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: **3** * Paranoid score: **5** * Final recommended bucket: **Actionable Moderate at minimum** ## 2. Signal breakdown Conservative signals: * **Security / forwarding policy bypass: +2** A failed VXLAN MDB source-list replace can remove pre-existing source entries and change multicast forwarding semantics. EXCLUDE mode can forward traffic that should be blocked, and INCLUDE mode can drop traffic that should be forwarded. * **Confidentiality impact plausible: +1** In EXCLUDE mode, traffic may be delivered where policy intended it not to be delivered. * **Integrity impact plausible: +1** The configured multicast forwarding policy can be corrupted logically. * **Availability impact realistic: +1** In INCLUDE mode, traffic that should be forwarded may be dropped. * **Requires CAP_NET_ADMIN in typical deployments: -2** Updating VXLAN MDB state is a control-plane operation and normally requires administrative network privileges. Conservative total: **3** Paranoid additions / adjustments: * **Common data-center networking exposure: +1** VXLAN is commonly used in virtualized, containerized, and data-center overlay networks, even though this specific path is not a default Internet-exposed packet parser. * **Reduced privilege / delegated network admin interpretation: +1 adjustment versus full -2 penalty** In practical deployments, VXLAN control may be reachable by container root, orchestrators, service accounts, or delegated CAP_NET_ADMIN rather than full host-root. This supports the paranoid score. Paranoid total: **5** No memory-corruption signals are awarded. The patch shows logical source-list rollback corruption, not UAF, OOB write, double-free, refcount takeover, arbitrary write, or privilege escalation. Call-site confidence: **high**. The replace path, add path, rollback path, and changed helper behavior are visible in the provided diff. ## 3. Reachability analysis The bug is triggered through VXLAN MDB control-plane configuration, specifically a failed replace of the source list for an existing `(*,G)` remote entry. It is not directly triggered by ordinary VXLAN data packets from the network. In typical host deployments, the attacker needs CAP_NET_ADMIN or equivalent privileges to manipulate VXLAN MDB state, so the conservative interpretation applies an admin privilege penalty. However, in containerized or orchestrated environments, network administration may be delegated to less-than-full host-root actors, which makes PR:L-style practical triage reasonable for the paranoid score. The affected functionality is configuration-dependent because VXLAN MDB support and multicast filtering must be in use. It is still relevant for data-center and overlay networking environments where forwarding policy correctness is security-sensitive. ## 4. Severity interpretation This behaves like an **actionable Moderate** issue rather than a Low correctness-only bug, because it can change forwarding behavior and potentially bypass multicast source filtering policy. It does **not** look like an Important-class memory-safety issue. The realistic impact is policy corruption, unintended forwarding, or unintended dropping of traffic. Theoretical privilege escalation is not supported by the patch. Because the issue affects VXLAN forwarding policy and can invert INCLUDE / EXCLUDE behavior, it should not be auto-closed purely because the CVSS-like score is moderate. ## 5. One-sentence report phrase A failed VXLAN MDB source-list replace can corrupt the logical source state of an existing multicast remote entry, causing EXCLUDE filters to forward traffic that should be blocked or INCLUDE filters to drop traffic that should be forwarded, with typical triggering requiring CAP_NET_ADMIN or delegated network-control privileges. ## 6. Manual review recommendation **MANUAL CHECK RECOMMENDED** YES REQUIRES MANUAL CHECK because this is a network forwarding policy bypass in VXLAN MDB control-plane handling, even though no kernel memory corruption or direct remote packet-triggered path is shown. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: vxlan: mdb: Fix source list corruption on a failed replace Commit: 5bc8fc1d2ff802eec839e03adef5df597421898d Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5bc8fc1d2ff802eec839e03adef5df597421898d Commit description: When replacing the source list of an MDB remote entry, all existing sources are first marked for deletion and vxlan_mdb_remote_srcs_add() is then called to add the new source list. Sources present in the new list have their deletion mark cleared, and any sources left marked afterwards are removed. If vxlan_mdb_remote_srcs_add() fails partway through, its error path deletes all entries on the remote's source list. That rollback is only correct for its other caller, vxlan_mdb_remote_add(), where the remote was just allocated and the list contains solely entries added during the call. On the replace path the list also holds pre-existing sources, so a failed replace tears them down together with their (S, G) forwarding entries instead of leaving the entry unchanged. This is reachable from an existing (*, G) remote. An EXCLUDE filter that loses sources starts forwarding traffic that should be blocked, while an INCLUDE filter that loses sources drops traffic that should be forwarded. Mark entries created during the current pass with a new VXLAN_SGRP_F_NEW flag. On failure, delete only those entries and clear the deletion mark on the pre-existing ones, so a failed replace leaves the source list untouched. Retain the flag until the whole operation succeeds and then clear it. Also stop vxlan_mdb_remote_src_add() from deleting a pre-existing entry it only looked up when adding that entry's forwarding entry fails. Fixes: a3a48de ("vxlan: mdb: Add MDB control path support") Cc: stable@vger.kernel.org Signed-off-by: James Raphael Tiovalen Reviewed-by: Ido Schimmel Reviewed-by: Antoine Tenart Reviewed-by: Nikolay Aleksandrov Link: https://patch.msgid.link/20260720160428.249356-1-jamestiotio@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: drivers/net/vxlan/vxlan_mdb.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=5bc8fc1d2ff802eec839e03adef5df597421898d ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-68116 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68116 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:H/UI:N/S:U/C:L/I:L/A:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L The Best / paranoid CVSS score: 4.5 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: 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).