From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89478][MODERATE 7.0] sctp: drop a chunk if its transport was removed Date: Sat, 12 Sep 2026 06:44:07 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89478 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: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: c6c86a5e62a4fec36692ddd64b9144b660f71f96 List-Id: CVE: CVE-2026-89478 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: sctp: drop a chunk if its transport was removed Commit: c6c86a5e62a4fec36692ddd64b9144b660f71f96 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6c86a5e62a4fec36692ddd64b9144b660f71f96 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89478 Analysis date: Sat, 12 Sep 2026 06:44:07 -0400 ActionableScore: 6 ActionableScore lower bound: 5 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-2026-89478 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89478 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-2026-89478 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89478 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'An SCTP use after free can occur when a packet keeps a chunk.transport pointer while an authenticated ASCONF DEL-IP removes the same transport from the association. A DATA chunk from that packet can restore the removed transport into asoc peer last_data_from, and a later delayed SACK can carry the stale pointer into transport selection where freed transport state is read. This is a network reachable race condition with AC:H because the vulnerable window depends on packet backlog or direct receive timing around socket locking and transport removal. For the CVSS the PR:N is used for the paranoid score because a remote SCTP peer may trigger the path without local code execution on the target once it can reach and form the required association. If SCTP AUTH keys or association policy restrict the peer set, PR:L is a more realistic base interpretation. Impact is at least remote denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact because the primitive is UAF in kernel networking code.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) SKIP CVE-2026-89478 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE UAF NETWORK LINUS KPANIC PACKET DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 5 * Conservative score: 5. No floor or cap changed the score. * Raw paranoid score: 6 * Paranoid score: 6. No floor or cap changed the score. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown Conservative signals: * +2 Real UAF / active lifetime violation. The commit establishes that an SCTP transport can be removed from the association, later freed by RCU, and then read through a stale pointer during delayed SACK transport selection. * +2 Remote reachable / directly network-triggerable. The trigger is driven by SCTP protocol traffic, specifically authenticated ASCONF DEL-IP plus affected packet processing. This is not a local syscall-only or host-admin-only path. * +1 Reliable kernel crash / strong DoS. Reading freed transport state in kernel networking code is a realistic kernel fault / DoS condition. Paranoid additional signal: * +1 Attacker-influenced active-object lifetime manipulation. The remote SCTP peer can influence the relevant transport removal and packet/chunk sequence, and the stale object is later consumed in active SCTP output processing rather than only in a cleanup destructor. Negative signals: * 0 No hard-race penalty applied. The bug is a race, but the supplied evidence describes reachable backlog and direct receive windows rather than a proven one-shot or externally uncontrollable timing condition. * 0 No host-admin penalty applied. Host-admin-equivalent privilege is not required by the supplied trigger model. * 0 No rare-subsystem penalty applied. SCTP is less common than TCP, but the subsystem being optional or less common is not enough by itself for a negative point. Important non-awarded signals: * Strong exploitation leverage +2 not awarded. Controlled reclaim, attacker-shaped replacement object, arbitrary read/write, callback control, refcount takeover, or demonstrated LPE is not established. * Structured stale-object leverage was not separately stacked beyond the paranoid lifetime-manipulation point. The same stale transport consumption is the basis for the unresolved active-object concern. * Confidentiality and integrity points not awarded. The patch supports UAF and DoS, but not a concrete disclosure path or unauthorized modification primitive. * Extra availability point not awarded. The same stale transport use supports the kernel crash/DoS signal and is not counted again. * Concrete repeated release/refcount signal not awarded. The later vulnerable operation reads freed transport state, but the patch does not establish a second put/free/refcount mutation on the same dangling reference. Repeated release/refcount check: * First release can end lifetime: yes, sctp_transport_free drops the association reference and the transport can later be freed after remaining references go away. * Exact same reference survives: yes, the stale transport pointer can be carried through chunk->transport and asoc->peer.last_data_from. * Second operation is a real lifetime/refcount mutation: no, the later described operation is reading freed transport state in sctp_outq_select_transport. * +1 Concrete repeated release/refcount awarded: no. * Paranoid repeated-refcount leverage +1 awarded: no. * FLOOR 5 applied: no explicit floor needed because the conservative raw score is already 5. 3. Reachability analysis The evaluated attacker is a remote SCTP peer that can form or participate in an SCTP association and send authenticated ASCONF DEL-IP traffic. The issue is network-triggerable through SCTP packet processing and does not require local code execution on the target host. The ASCONF DEL-IP requirement means the peer must satisfy SCTP authentication or association policy, so deployments with strict SCTP AUTH keys or trusted peer lists may reduce practical exposure. That restriction does not make the issue host-admin-only. HostAdminRequired is NO because the supplied trigger is a protocol peer, not a host administrator. NamespaceScopedPrivilege is NO because the trigger is not based on namespace-scoped Linux capabilities. No prior local privileged setup by the attacker is established, although the vulnerable endpoint must have SCTP in use and reachable. The race is timing-dependent, but the same remote peer can influence the packet sequence and transport removal. The supplied evidence does not justify treating it as a rare one-shot race for ActionableScore purposes. 4. Primitive and severity interpretation The exact primitive is a real use-after-free of an SCTP transport object. The stale object is an active structured networking object, not fixed stale storage. The stale use is broader than cleanup-only behavior because the freed transport pointer can be placed into asoc->peer.last_data_from and later consumed by delayed SACK output transport selection. This is CLASS_B. It is a concrete kernel lifetime bug with active-object stale use, but the patch does not establish CLASS_A evidence such as controlled reclaim, directed write, arbitrary read/write, callback influence, credential manipulation, or demonstrated privilege escalation. Demonstrated consequence is remote kernel DoS through UAF-triggered invalid access. Speculative consequence is stronger exploitation through post-free object reuse, but that is not proven. Because the UAF is network reachable and involves active SCTP transport state rather than a narrow cleanup-only stale dereference, Important-vs-Moderate exploitation leverage remains unresolved. ImportantCandidate is YES because this is a network-reachable active-object UAF requiring manual exploitation-leverage review. AutoDowngradeAllowed is NO because automatic closure would discard a concrete unresolved kernel lifetime primitive in packet-processing code. Likely operational severity is at least Actionable Moderate. It is a Strong Important candidate only if later evidence shows controlled reuse, useful stale field consumption after replacement, information disclosure, memory corruption beyond stale read, or privilege escalation. 5. One-sentence report phrase An SCTP peer can trigger a race where an authenticated ASCONF DEL-IP removes a transport while queued DATA processing later reuses the stale transport pointer for delayed SACK selection, causing a network-reachable kernel UAF and possible DoS. 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a real network-reachable active-object UAF in SCTP transport handling, with DoS demonstrated and unresolved exploitation leverage beyond crash. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: sctp: drop a chunk if its transport was removed Commit: c6c86a5e62a4fec36692ddd64b9144b660f71f96 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c6c86a5e62a4fec36692ddd64b9144b660f71f96 Commit description: sctp_rcv() resolves the transport once per packet and leaves it in chunk->transport. The lookup reference, or the one sctp_add_backlog() takes if the socket is owned by userspace, keeps it around until the chunk has been processed. An authenticated ASCONF DEL-IP can remove it in the meantime. sctp_assoc_rm_peer() takes the transport out of the association and calls sctp_transport_free(), which tags it dead and drops the reference the association held. There is a window on both paths: the packet can sit on the socket backlog, and on the direct path the lookup completes before bh_lock_sock(). The DATA chunk in that packet puts the removed transport back into asoc->peer.last_data_from. Once the packet is done that reference goes away and the transport is freed by RCU, so the next delayed SACK carries the pointer into the SACK chunk and sctp_outq_select_transport() reads the freed transport's state. Drop the chunk in sctp_inq_push(), next to the existing rcvr->dead check. Both paths reach it with the association's socket lock held. The peer retransmits it. Fixes: 1da177e ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Hyunwoo Kim Acked-by: Xin Long Link: https://patch.msgid.link/aoUJHQmxL0LFIMCw@v4bel Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/sctp/inqueue.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=c6c86a5e62a4fec36692ddd64b9144b660f71f96 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89478 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89478 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:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 8.1 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: 5 Paranoid ActionableScore: 6 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).