From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-97612][MODERATE 7.0] net: mpls: clear inner_protocol when the last label is popped Date: Fri, 25 Sep 2026 10:31:18 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-97612 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 011e17b5cae19b9f6a150923275e41c278de64f0 List-Id: CVE: CVE-2026-97612 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: net: mpls: clear inner_protocol when the last label is popped Commit: 011e17b5cae19b9f6a150923275e41c278de64f0 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=011e17b5cae19b9f6a150923275e41c278de64f0 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97612 Analysis date: Fri, 25 Sep 2026 10:31:18 -0400 ActionableScore: 5 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97612 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97612 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-97612 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-97612 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:H/I:H/A:H';*CWE-787;CWE-195;CWE-681;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7.8';DESCR 'A stale MPLS inner network header can survive after the last MPLS label is popped. Open vSwitch can later reuse this stale header after MPLS recirculation and fragmentation, causing a negative network offset to pass a signed bounds check. The negative value is converted to an unsigned length and used by memcpy in prepare_frag, resulting in a massive kernel out of bounds write. For the CVSS the PR:L because reliable triggering requires control of Open vSwitch flow configuration or equivalent delegated network administration capabilities. The issue is not directly network reachable through packet traffic alone, although a remote peer may supply packets after a privileged actor has installed a vulnerable MPLS flow configuration. Impact includes kernel crash and may include confidentiality integrity and privilege escalation consequences because the patch context demonstrates an out of bounds kernel write. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) YES REMOTE KASAN SKB HARDWARE LINUS IPV6 KPANIC PACKET KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 PrimitiveClass=CLASS_A RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 4 * Conservative score: 5 * Raw paranoid score: 4 * Paranoid score: 5 * Applied conservative floor: 4 -> 5. A concrete attacker-influenced kernel out of bounds write must not be automatically closed as ordinary Moderate. * Applied paranoid floor: 4 -> 5. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 Strong kernel corruption primitive. A stale inner_network_header creates a negative skb_network_offset. The signed bounds check accepts the negative value, which is widened to unsigned int and passed as hlen to memcpy. The resulting approximately 4 GiB copy writes beyond the small per CPU l2_data buffer. * +1 Reliable kernel crash or strong DoS. The supplied reproducer shows a supervisor kernel page fault in memcpy through prepare_frag and ovs_fragment. * +1 Integrity plausible. The vulnerable operation is a real kernel write past the intended destination buffer. The exact overwritten objects and useful post corruption state are not established. * Controlled reclaim, arbitrary kernel read write, controlled target selection, callback control, credential corruption, information disclosure, and demonstrated privilege escalation are not established. * Direct remote reachability is not awarded. A remote packet alone does not establish the complete sequence because the MPLS push pop recirculation and fragmentation action path requires a relevant Open vSwitch flow configuration. * Local unprivileged trigger is not awarded. The supplied material does not establish that an ordinary unprivileged user can create the necessary Open vSwitch MPLS action configuration. * No host admin penalty is applied. The supplied evidence suggests network administration or Open vSwitch control plane access is relevant, but it does not prove that host admin equivalent privilege is required for every deployment. * No niche subsystem penalty is applied. Open vSwitch MPLS configuration is specialized, but no evidence proves that an attacker cannot reach it in an evaluated deployment. * No extra Availability point is awarded. The demonstrated Oops is already counted as the reliable kernel crash signal. * No paranoid bonus is awarded. The concrete out of bounds write is serious, but the available evidence does not establish a distinct controlled reclaim, target selection, or post corruption exploitation primitive beyond the same overwrite. 3. Reachability analysis The direct trigger is an Open vSwitch datapath sequence involving MPLS push, removal of all labels, recirculation, another MPLS push, and the OVS fragmentation path. The attacker must be able to cause packets to execute a matching vulnerable OVS action graph and reach ovs_fragment. The supplied evidence supports that packet contents can reach the copy source and that the malformed state produces the negative length. It does not establish who can install or modify the required OVS flows. In common host deployments, configuring OVS flows and MPLS actions is performed by an administrator or a delegated network management component. However, the exact capability checks and whether all required stages can be completed from an attacker controlled network namespace are not supplied. HostAdminRequired is therefore UNKNOWN. NamespaceScopedPrivilege is also UNKNOWN. The existence of network namespaces or potentially delegated CAP_NET_ADMIN would not by itself prove that the complete OVS configuration and vulnerable execution path is namespace scoped. This is not directly remote reachable in the strict sense because untrusted network traffic requires prior vulnerable local control plane configuration. A remote peer may nevertheless provide packet data after a privileged or delegated actor has installed the relevant OVS MPLS actions. 4. Primitive and severity interpretation The exact primitive is an attacker influenced out of bounds kernel write caused by signed to unsigned conversion of a stale negative skb header offset. The stale inner header metadata is not a use after free. It is stale protocol state that is later trusted by ovs_fragment. The memcpy destination starts at a small per CPU l2_data buffer, while the derived length can become approximately 4 GiB. The supplied trace confirms an attempted supervisor mode write in memcpy with RDX equal to 0xfffffff8. This is stronger than a NULL pointer dereference or crash only invalid state. The write target begins at a fixed kernel buffer and the supplied evidence does not show controlled placement, a chosen final target, controlled object replacement, callback dispatch, arbitrary read write, or a demonstrated LPE chain. Therefore, this is CLASS_A due to a concrete attacker influenced OOB write, but it is not scored as a demonstrated arbitrary kernel write or demonstrated privilege escalation. ImportantCandidate is YES because a concrete kernel memory corruption primitive exists and the practical reachability and post corruption leverage require manual investigation. AutoDowngradeAllowed is NO because automatically treating the bug as only an OVS crash could discard a real out of bounds kernel write primitive. Likely operational severity is at least actionable Moderate. It can become an Important classification if manual review confirms that a below host admin actor can install the necessary OVS actions, influence packet payloads, and obtain useful corruption of adjacent per CPU state. 5. One-sentence report phrase A stale MPLS inner header offset can become a negative value that bypasses a signed bounds check and is widened into an approximately 4 GiB memcpy length in the Open vSwitch fragmentation path, causing a kernel out of bounds write and crash. 6. Manual review recommendation MANUAL CHECK REQUIRED A concrete kernel out of bounds write is established, but the complete privilege boundary for OVS flow setup and the practical control over the overwritten kernel state are unresolved. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net: mpls: clear inner_protocol when the last label is popped Commit: 011e17b5cae19b9f6a150923275e41c278de64f0 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=011e17b5cae19b9f6a150923275e41c278de64f0 Commit description: skb_mpls_push() records the pre-encapsulation network header once, gated on !skb->inner_protocol. skb_mpls_pop() never clears that record, so it outlives the encapsulation it describes. Open vSwitch can then re-push MPLS onto a packet whose inner_network_header still points at the older, deeper offset: push a label, pop every label, recirculate (ovs_flow_key_update() re-derives key->eth.type and resets network_header, but leaves inner_*), then push again. ovs_fragment() trusts the record: skb->network_header = skb->inner_network_header; so skb_network_offset() goes negative. The bound check is signed: if (skb_network_offset(skb) > MAX_L2_LEN) a negative offset passes it, and prepare_frag() widens the value: unsigned int hlen = skb_network_offset(skb); memcpy(&data->l2_data, skb->data, hlen); which is a ~4GiB memcpy out of a 30-byte per-CPU buffer. Reproduced on v7.3-rc1. RDX is the truncated length, (unsigned int)(-8): BUG: unable to handle page fault for address: ffffe8ffffc16000 #PF: supervisor write access in kernel mode Oops: 0002 [#1] SMP KASAN NOPTI RIP: 0010:memcpy+0x8/0x20 RDX: 00000000fffffff8 RSI: ffff888105d732db RDI: ffffe8ffffc16000 prepare_frag+0x3df/0x4e0 ovs_fragment+0x589/0x7e0 do_output+0x4ce/0x5e0 do_execute_actions+0x55d2/0x7b30 ovs_execute_actions+0xea/0x450 Same root-cause shape as commit 975b5b0 ("ipv6: sr: restore network header before routing and forwarding"): a stale network header offset reaching a consumer that widens it. Here it originates in the MPLS push/pop path. Clear inner_protocol once the packet is no longer MPLS, so a later push re-records the current header. net/sched/act_mpls.c is the only other skb_mpls_pop() caller and gets the same fix; sch_frag.c saves and restores inner_protocol around fragmentation in the same way OVS does. Fixes: 48d2ab6 ("net: mpls: Fixups for GSO") Cc: stable@vger.kernel.org Signed-off-by: Fourie Zhang Acked-by: Jiri Benc Link: https://patch.msgid.link/20260902092719.2874481-1-fouriezhang@tencent.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/sched/act_mpls.c net/core/skbuff.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=011e17b5cae19b9f6a150923275e41c278de64f0 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97612 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97612 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:H/I:H/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7.8 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: 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: YES 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).