From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-97615][LOW] net: bridge: use option bits for CFM/MRP frame handlers Date: Fri, 25 Sep 2026 15:19:30 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-97615 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: unknown X-AL-KERNEL-Commit: 994fd705ca498223d188024cde833739a9dddbd2 List-Id: CVE: CVE-2026-97615 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: net: bridge: use option bits for CFM/MRP frame handlers Commit: 994fd705ca498223d188024cde833739a9dddbd2 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=994fd705ca498223d188024cde833739a9dddbd2 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97615 Analysis date: Fri, 25 Sep 2026 15:19:30 -0400 ActionableScore: 2 ActionableScore lower bound: unknown 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-2026-97615 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97615 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-2026-97615 LOW https://www.kernelcve.org/list/?q=CVE-2026-97615 CHECK WITH IMPACT FROM ORIG NN LOW 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:L/A:L';*CWE-664;CWE-665;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'A logic error in Linux bridge CFM and MRP handling allows one global frame handler list node to be inserted into frame handler lists of multiple bridges. Removing the handler from one bridge can then corrupt list state associated with another bridge and can disable or misdirect CFM or MRP special frame processing. For the CVSS the PR:L score is used for the paranoid assessment because a delegated CAP_NET_ADMIN user, container root, or service account may be able to configure bridge protocol instances without full host root privileges. The issue is not directly network reachable because creating CFM MEP or MRP instances is the required trigger. Remote Layer 2 traffic may be affected after the bridge has entered the corrupted state. Impact is limited availability degradation and possible limited integrity impact on bridge control protocol processing. No UAF, out of bounds access, arbitrary write, kernel crash, or privilege escalation primitive is demonstrated by this patch.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES INIT SKB IMPROVEONLY LINUS PACKET NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2 * Raw paranoid score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate**:: No floor or cap was applied. 2. Signal breakdown * +1 Concrete cross-list state corruption. The same static `br_frame_type.list` hlist node can be linked into frame lists for multiple bridges. A later `hlist_del_rcu()` uses linkage overwritten by the later insertion and can modify the other bridge list. * +1 Limited protocol availability impact. The resulting state can disable or misdirect CFM or MRP frame handling for another affected bridge, disrupting the relevant bridge-control protocol processing. Important non-awarded signals: * No real UAF was established. The affected CFM and MRP `br_frame_type` objects are static objects and the patch does not show their release or reuse after free. * No controlled reclaim, attacker-controlled replacement, arbitrary write, callback hijack, or directed kernel memory corruption is established. * No reliable kernel crash, panic, OOB access, information disclosure, privilege escalation, or authorization bypass is established. * No direct remote reachability was established. Received Layer 2 frames may encounter already-corrupted handler state, but they do not create the cross-bridge list corruption by themselves. * No local-unprivileged-trigger point was awarded. The supplied patch does not establish that an ordinary unprivileged user can create the required bridges and CFM or MRP instances. * No CAP_NET_ADMIN or host-administrator penalty was applied. The required capability scope is not visible in the supplied context, so host-admin equivalence is unresolved rather than assumed. * No niche-subsystem penalty was applied. CFM and MRP are uncommon, but the supplied evidence does not prove that an attacker cannot instantiate the required topology when permitted to manage a network namespace. * No confidentiality or integrity point was awarded. Incorrect CFM or MRP handler processing is a protocol-functionality problem, but the patch does not establish unauthorized modification of protected data or a security boundary. 3. Reachability analysis The direct trigger requires enabling CFM or MRP on more than one bridge and later removing an instance from one of those bridges. This is a network control-plane operation, not a packet-only trigger. An attacker needs sufficient authority to create and configure bridges, ports, and CFM MEP or MRP instances. The exact capability checks for the relevant bridge netlink operations are not present in the supplied patch. Linux bridge configuration commonly uses CAP_NET_ADMIN evaluated against a target network namespace, but the complete sequence has not been verified here. Therefore, HostAdminRequired is UNKNOWN and NamespaceScopedPrivilege is UNKNOWN. No special hardware, firmware interaction, sysctl, boot parameter, or race condition is shown. The list corruption is a deterministic lifecycle/configuration sequence once the necessary bridge protocol instances can be configured. CFM and MRP support must be compiled and enabled, but this alone is not treated as a scoring penalty. 4. Primitive and severity interpretation The exact primitive is deterministic corruption of linked-list membership for static CFM or MRP handler objects. A single global `hlist_node` is inserted into multiple per-bridge `frame_type_list` lists. Its `next` and `pprev` linkage then represents only the most recent insertion, while previous list heads can still reference it. Deleting the handler from one bridge can unlink or alter state associated with another bridge. This is not an active-object use-after-free. The node remains static, is not freed, and the supplied evidence does not show stale post-lifetime dereference, allocator reuse, refcount mutation, or a second release operation. It is therefore not a repeated release or refcount case. The demonstrated consequence is bridge protocol handler state corruption, potentially causing CFM or MRP frames to be processed incorrectly or not processed for an affected bridge. A kernel crash remains speculative because the patch and supplied context do not show an invalid dereference after the corruption. Exploitation leverage beyond protocol disruption is not established. The issue is classified as CLASS_C because it is a constrained list-corruption and invalid-state condition with no independently useful memory-corruption primitive. It is not an ImportantCandidate. AutoDowngradeAllowed is YES because the available evidence supports a limited configuration-induced protocol DoS or logic failure, without unresolved UAF, controlled corruption, ownership violation, or security-boundary bypass. Likely operational severity is Ordinary Moderate or Low-like. Manual confirmation is still useful because bridge CFM and MRP deployments may use these protocols for industrial Ethernet or topology-management functions, where protocol disruption can have operational impact disproportionate to the kernel-memory primitive. 5. One-sentence report phrase A shared static CFM or MRP frame handler node could be linked into multiple Linux bridge handler lists, so removing it from one bridge could corrupt another bridge handler list and disrupt CFM or MRP protocol processing. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Verify the exact rtnetlink capability checks and namespace scope for CFM and MRP creation, and verify whether corrupted handler-list traversal can produce a kernel fault in affected kernel versions. No UAF or attacker-controlled memory-write primitive is currently established. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net: bridge: use option bits for CFM/MRP frame handlers Commit: 994fd705ca498223d188024cde833739a9dddbd2 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=994fd705ca498223d188024cde833739a9dddbd2 Commit description: CFM and MRP register a global br_frame_type whose hlist_node is linked into the per-bridge frame_type_list when the first MEP/MRP instance is created. Enabling the protocol on multiple bridges therefore inserts the same node into multiple lists. Unregistering it on one bridge then corrupts list state belonging to another. These handlers can only be installed once per bridge, and they are uncommon. Track their per-bridge enable state with net_bridge option bits, which already live on the Rx hot cache line, and dispatch the matching handler directly from the receive path. Check both bits together first as an unlikely case. Remove the generic frame_type_list and br_frame_type helpers, which have had no other users since CFM and MRP were added. That shrinks struct net_bridge by 8 bytes and drops the list walk from the fast path. When neither protocol is compiled in, BR_CFM_MRP_OPTS is 0 and the compiler prunes the branch. Fixes: 90c628d ("net: bridge: extend the process of special frames") Fixes: dc32cbb ("bridge: cfm: Kernel space implementation of CFM. CCM frame RX added.") Cc: stable@vger.kernel.org Reported-by: Vega Suggested-by: Nikolay Aleksandrov Co-developed-by: Yilin Zhu Signed-off-by: Yilin Zhu Signed-off-by: Zhiling Zou Acked-by: Nikolay Aleksandrov Link: https://patch.msgid.link/0345b9d5aa60ba416f6738ff1b87140f0a749cb8.1788417901.git.zhilinz@nebusec.ai Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/bridge/br_cfm.c net/bridge/br_device.c net/bridge/br_input.c net/bridge/br_mrp.c net/bridge/br_private.h 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=994fd705ca498223d188024cde833739a9dddbd2 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97615 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97615 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:H/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L The Best / paranoid CVSS score: 4.4 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: unknown 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).