From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99053][MODERATE 7.0] tipc: hold a reference to nodes found by link name Date: Mon, 26 Oct 2026 15:36:03 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99053 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: 4 X-AL-KERNEL-Commit: b60259d4047fbb735476c729dcf9306a038b6110 List-Id: CVE: CVE-2026-99053 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: tipc: hold a reference to nodes found by link name Commit: b60259d4047fbb735476c729dcf9306a038b6110 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b60259d4047fbb735476c729dcf9306a038b6110 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99053 Analysis date: Mon, 26 Oct 2026 15:36:03 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: TIPC generic-netlink link handlers can race peer-node retirement, write through a freed node’s lock, and subsequently consume stale link and media-address state. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99053 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99053 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-2026-99053 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99053 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in tipc_node_find_by_name can return a node after leaving RCU lacking a retained kref. Timer driven peer cleanup can then free the node before LINK_SET, LINK_GET, or LINK_RESET_STATS locks or accesses it, producing a confirmed slab use after free in _raw_read_lock_bh. For the CVSS the PR:L value reflects that reliable triggering requires a local process able to issue privileged TIPC generic netlink link commands, typically with CAP_NET_ADMIN. AC:H reflects the required timing race with peer cleanup. The confirmed primitive includes access and lock state modification through a freed node pointer. This supports kernel crash and possible corruption of a reclaimed slab object, while controlled disclosure or privilege escalation is not proven. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because a specific evidence based protection or manual review veto was applied and FD false positive review allowed a downgrade. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were V33_ACTIVE_STATE_BOUNDARY_CANDIDATE and IMPORTANT_CANDIDATE_MANUAL_REVIEW and KP_ONLY_DOWNGRADE_VETO and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH. The independent weaker Aegis shadow evaluated CVSS 1.6 and ActionableScore 5 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE OOB LOCK DANGER TIPC ERRORPATH UAF HARDWARE LINUS KPANIC PACKET V33_ACTIVE_STATE_BOUNDARY_CANDIDATE IMPORTANT_CANDIDATE_MANUAL_REVIEW KP_ONLY_DOWNGRADE_VETO DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 4. * Conservative score: 4; no floor or cap changed it. * Raw paranoid score: 5. * Paranoid score: 5; no floor or cap changed it. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 real UAF: RCU lookup returns `tipc_node` without retaining a kref; timer cleanup can free it before handler use. * +1 reliable crash/strong DoS: KASAN confirms a four-byte post-free spinlock write in `_raw_read_lock_bh`. * +1 structured stale-object leverage: handlers subsequently consume active node/link state; LINK_SET additionally uses `node->links[bearer_id].maddr` in `tipc_bearer_xmit()`. * Paranoid +1: the confirmed stale-state write followed by privileged network-state consumption forms a specific unknown namespace/delegated-interface trust-boundary chain. * No race penalty: the interleaving is required, but supplied evidence does not establish narrow, one-shot, or externally uncontrollable timing. * No controlled reclaim, attacker-shaped replacement object, arbitrary write, disclosure, LPE, or proven C/I impact. * No extra availability point for the same crash. * NEW52/B5-R does not apply: no retry-accumulated OOB write. B3-PENDING and B4-PENDING also do not apply. 3. Reachability analysis A local process invokes TIPC generic-netlink LINK_SET, LINK_GET, or LINK_RESET_STATS while timer-driven peer cleanup retires the selected node. The hints indicate CAP_NET_ADMIN is typically required, but the supplied source does not identify the governing user/network namespace or prove that the complete trigger is host-admin-only or fully namespace-scoped. TIPC peer/down-node setup is required; no special hardware is involved. The race is concrete, but its practical repeatability is unresolved. 4. Primitive and severity reading This is an active structured-object UAF, not fixed stale storage or a cleanup-only dereference. The first demonstrated stale operation writes lock state into freed slab storage; later operations access link pointers/state, and LINK_SET passes a stale media address to transmission. That supports CLASS_B and a plausible crash, but not CLASS_A because reclaim control or directed corruption is absent. The concrete write, later privileged consumer, and credible but unresolved namespace/delegated-interface boundary require Important review under the active-state trust-boundary rule. Auto-downgrade is unsafe even though Important severity and host compromise are not proven. 5. One-sentence report phrase TIPC generic-netlink link handlers can race peer-node retirement, write through a freed node’s lock, and subsequently consume stale link and media-address state. 6. Manual review advice MANUAL CHECK REQUIRED Review capability namespace scope, trigger repeatability, slab reuse behavior, and whether stale link/media-address consumption can affect a more privileged network stack. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: tipc: hold a reference to nodes found by link name Commit: b60259d4047fbb735476c729dcf9306a038b6110 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b60259d4047fbb735476c729dcf9306a038b6110 Commit description: tipc_node_find_by_name() returns a node after dropping its RCU read lock without taking a reference. The LINK_SET, LINK_GET and LINK_RESET_STATS handlers then lock and access the node, racing with timer-driven cleanup of a down peer. Generic netlink serialization does not exclude the node timer. The following interleaving can leave a handler using a freed node: CPU 0: find the node under RCU and release the node read lock CPU 1: tipc_node_timeout() clears the links and unlinks the down node CPU 1: drop the list and timer references, queuing tipc_node_free() CPU 0: leave the RCU read-side critical section CPU 1: complete the grace period and free the node CPU 0: acquire the node lock through the stale pointer LINK_SET also uses the node's media address after releasing the node lock, when passing queued packets to tipc_bearer_xmit(). KASAN on v7.3-rc5 reported: BUG: KASAN: slab-use-after-free in _raw_read_lock_bh Write of size 4 at addr ffff88807e06f008 by task poc/92 Call Trace: _raw_read_lock_bh kernel/locking/spinlock.c:287 tipc_nl_node_set_link net/tipc/node.c:2475 genl_family_rcv_msg_doit net/netlink/genetlink.c:1114 genl_rcv_msg net/netlink/genetlink.c:1209 netlink_rcv_skb net/netlink/af_netlink.c:2575 Allocated by task 0: tipc_node_create net/tipc/node.c:539 tipc_node_check_dest net/tipc/node.c:1196 tipc_disc_rcv net/tipc/discover.c:252 Freed by task 92: kfree mm/slub.c:6801 rcu_core kernel/rcu/tree.c:2919 Last potentially related work creation: __call_rcu_common.constprop.0 kernel/rcu/tree.c:3181 tipc_node_timeout net/tipc/node.c:814 Acquire a reference to the selected node with kref_get_unless_zero() before leaving RCU, returning NULL if the node has already been released. Release that reference on every caller exit after the last node access, including transmission in LINK_SET. Keep the existing link lookup order and locking so concurrent link removal still takes the existing error paths. Fixes: 6a939f3 ("tipc: Auto removal of peer down node instance") Cc: stable@vger.kernel.org Signed-off-by: Chengfeng Ye Link: https://patch.msgid.link/20260928161246.1895273-1-nicoyip.dev@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: kernel/locking/spinlock.c net/tipc/node.c net/netlink/genetlink.c net/netlink/af_netlink.c net/tipc/discover.c mm/slub.c kernel/rcu/tree.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=b60259d4047fbb735476c729dcf9306a038b6110 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99053 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99053 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:L/I:L/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 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: 4 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).