From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-97958][LOW] net/sched: cls_api: Don't replay RTM_GETCHAIN in tc_ctl_chain(). [ Upstream Date: Fri, 25 Sep 2026 10:17:56 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-97958 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: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: a1c2840d95af1fa3d83ba71e23fa0c674a4c6796 List-Id: CVE: CVE-2026-97958 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: net/sched: cls_api: Don't replay RTM_GETCHAIN in tc_ctl_chain(). [ Upstream Commit: a1c2840d95af1fa3d83ba71e23fa0c674a4c6796 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a1c2840d95af1fa3d83ba71e23fa0c674a4c6796 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97958 Analysis date: Fri, 25 Sep 2026 10:17:56 -0400 ActionableScore: 1 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-2026-97958 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97958 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-2026-97958 LOW https://www.kernelcve.org/list/?q=CVE-2026-97958 CHECK WITH IMPACT FROM ORIG NN MODERATE 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-835;**CWE-400;CWE-667;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A local denial of service can occur in tc_ctl_chain because RTM_GETCHAIN requests are replayed after EAGAIN when the sending netlink socket does not receive its responses and its receive buffer becomes full. The repeated replay can consume CPU while holding RTNL, trigger hung task reports, and block traffic control and other network configuration operations. For the CVSS the PR:L reflects that the attacker normally needs CAP_NET_ADMIN or equivalent delegated network administration capability, but does not necessarily need full host root privileges. The issue is not directly network reachable because it is triggered through local rtnetlink control plane operations rather than packet traffic. Base impact is availability degradation. Under sustained abuse the availability impact may be high due to CPU consumption and RTNL contention.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES REMOTE NETWORK HARDWARE DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 1 * Conservative score: 1 * Raw paranoid score: 1 * Paranoid score: 1 * Final recommended bucket: **Ordinary Moderate**:: No floor or cap applies. 2. Signal breakdown * +1 Reliable strong DoS. Repeated RTM_GETCHAIN replay after netlink returns EAGAIN can keep tc_ctl_chain running, consume CPU, hold RTNL, trigger Hung Task reports, and block traffic-control and related rtnetlink configuration operations. * +0 Remote reachability. The vulnerable path is reached through local rtnetlink control-plane messages, not ordinary network packets. * +0 Local unprivileged trigger. The supplied patch does not establish that an ordinary host user can complete the required traffic-control operations without delegated CAP_NET_ADMIN or equivalent capability. * +0 Memory corruption. No UAF, stale pointer, double release, invalid free, OOB access, refcount misuse, or attacker-controlled kernel memory mutation is established. * +0 Confidentiality and integrity. The replay loop causes CPU and RTNL contention only. No disclosure or unauthorized modification primitive is shown. * +0 Additional availability point. The CPU hog and blocked RTNL path are the same demonstrated DoS consequence and are not counted twice. * +0 Race penalty. This is deterministic replay on EAGAIN when the receive buffer is full, not a narrow timing race. * +0 privilege penalty. Host-admin-equivalent privilege is not positively established. The exact rtnetlink capability scope and complete setup path are not visible in the supplied context. CWE candidates are CWE-835, CWE-400, and CWE-667. 3. Reachability analysis The attacker sends RTM_GETCHAIN requests on a local rtnetlink socket and intentionally does not receive replies. Once the socket receive buffer is full, netlink delivery can return EAGAIN. The old replay handling restarts RTM_GETCHAIN indefinitely or for a prolonged period, resulting in CPU consumption and RTNL contention. Traffic-control operations normally involve CAP_NET_ADMIN. However, the supplied patch does not show the exact rtnetlink permission check, the relevant target network namespace, or whether every required stage can be completed by an attacker in a self-created user and network namespace. Therefore HostAdminRequired is UNKNOWN and NamespaceScopedPrivilege is UNKNOWN. No separate host-admin provisioning, special hardware, boot option, firmware condition, or uncommon kernel configuration is established by the patch. The required chain or qdisc state may need to exist, but this is ordinary traffic-control runtime state rather than evidence of a security boundary bypass. 4. Primitive and severity interpretation The exact primitive is an uncontrolled replay loop in a local rtnetlink control-plane handler after EAGAIN. The loop repeatedly re-enters tc_ctl_chain for RTM_GETCHAIN while the netlink response cannot be queued because the sender does not drain its receive buffer. This is a Class C availability issue. It is not a lifetime bug, memory-corruption bug, authorization bypass, or active-object ownership violation. There is no stale-object dereference, no repeated release or refcount mutation, no controlled reclaim, no arbitrary write, and no practical privilege-escalation mechanism established by the patch. The demonstrated consequence is local CPU consumption, Hung Task diagnostics, and blocking of RTNL-dependent network configuration. The likely operational severity is low to ordinary Moderate. Sustained abuse can materially affect network administration, but the supplied evidence does not support Important-grade kernel-corruption or security-boundary impact. ImportantCandidate is NO because no unresolved Class B lifetime or corruption primitive exists. AutoDowngradeAllowed is YES because the issue is a bounded logic and resource-consumption defect without demonstrated memory-safety, confidentiality, integrity, or authorization impact. 5. One-sentence report phrase A local attacker able to issue RTM_GETCHAIN rtnetlink requests can trigger repeated request replay after a full netlink receive buffer returns EAGAIN, causing CPU consumption and RTNL contention that may delay traffic-control updates and degrade system responsiveness. 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch establishes a local deterministic CPU-hog and control-plane DoS only, with no memory corruption, lifetime violation, privilege escalation, remote reachability, or security-boundary bypass evidence. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: cls_api: Don't replay RTM_GETCHAIN in tc_ctl_chain(). [ Upstream Commit: a1c2840d95af1fa3d83ba71e23fa0c674a4c6796 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a1c2840d95af1fa3d83ba71e23fa0c674a4c6796 Changed files: kernel/time/clockevents.c net/core/skbuff.c include/linux/skbuff.h net/netlink/af_netlink.c include/linux/rcupdate.h include/linux/rhashtable.h net/sched/cls_api.c include/net/netlink.h net/core/rtnetlink.c net/socket.c arch/x86/entry/syscall_64.c arch/x86/entry/entry_64.S 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=a1c2840d95af1fa3d83ba71e23fa0c674a4c6796 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97958 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97958 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:L/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: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: unknown Paranoid ActionableScore: 1 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).