From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98586][IMPORTANT] sctp: hold asoc or transport before mod_timer() in timer handlers [ Upstream Date: Sat, 24 Oct 2026 10:50:55 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98586 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: f7dea7eaea20fe9b80f8f77ba44d02b4a17f8050 List-Id: CVE: CVE-2026-98586 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: NO Patch: sctp: hold asoc or transport before mod_timer() in timer handlers [ Upstream Commit: f7dea7eaea20fe9b80f8f77ba44d02b4a17f8050 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f7dea7eaea20fe9b80f8f77ba44d02b4a17f8050 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98586 Analysis date: Sat, 24 Oct 2026 10:50:55 -0400 ActionableScore: 6 ActionableScore lower bound: 5 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: An SCTP timer-cleanup race can free an association or transport before the timer handler performs stale hold/put refcount mutations, producing a real active-object UAF with underflow and crash or corruption potential. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98586 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98586 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: IMPORTANT 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-2026-98586 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-98586 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT IMPORTANT AEGIS_AS=6 LEGACY=IMPORTANT RESULT=SAME (final reconciliation agrees; DECISION: both 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-911;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'An SCTP timer handler can call mod_timer() before acquiring the association or transport reference required by the rearmed timer. Concurrent timer cleanup can delete the timer, release its reference, and free the object before the handler calls the hold operation. The resulting use after free includes a reference count update on freed memory followed by a later put, which can cause refcount underflow, kernel memory corruption, and a kernel crash. For the CVSS the PR:N value is selected because a remote SCTP peer may influence association and transport timer activity without an authenticated account on the target. AC:H reflects the need to win a narrow race with timer cleanup. Remote trigger reliability and attacker control over object reuse are not established, so privilege escalation and arbitrary code execution remain unproven. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 8.1 and the production ActionableScore returned 6 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage IMPORTANT to IMPORTANT because KP specialist did not establish a qualifying panic. 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 KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 3.7 and ActionableScore 6 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was IMPORTANT. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) MAYBE OOB RACE UAF NETWORK TIMER LINUS KPANIC_UNSUPPORTED_REMOVED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 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: 5. * Conservative score: 5; no floor or cap changed it. * Raw paranoid score: 6. * Paranoid score: 6; no floor or cap changed it. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 Real UAF: cleanup may delete the rearmed timer, drop its reference, and free the association/transport before the handler calls `*_hold()`. * +1 Concrete repeated refcount/lifetime mutation: the cleanup put may end lifetime; the timer handler retains the exact object pointer, performs a stale refcount hold, and later puts that same object. * +1 Reliable kernel crash/strong DoS: the documented stale refcount operations can underflow the refcount and fault or corrupt kernel state. * +2 Plausible remote reachability: an unauthenticated SCTP peer can influence association/transport timer activity. Complete race reliability is not established. * -1 Hard timing: cleanup must occur specifically after `mod_timer()` and before the old `*_hold()`. * Paranoid +1: the stale `*_hold()` itself performs a write-like refcount mutation through storage whose original object lifetime may already have ended. Not awarded: controlled reclaim, attacker-selected target/payload, arbitrary write, disclosure, LPE, or C/I impact. The crash was not counted again as separate availability impact. CLASS_A is unsupported. 3. Reachability analysis The credible actor is a remote SCTP peer influencing timer and association lifecycle activity without authentication. The supplied evidence does not fully establish how reliably that peer induces the necessary cleanup interleaving, so effective host-admin requirements remain UNKNOWN rather than positively NO. No namespace capability, prior privileged setup, special hardware, or local UID requirement is established. The race is narrow, although network activity may permit repeated attempts. 4. Primitive and severity reading This is an active structured-object UAF, not fixed stale storage. Cleanup can release the timer’s lifetime reference and destroy the association or transport while the handler still holds its pointer. The later stale `hold` and eventual `put` actively mutate refcount state; this is category B post-lifetime mutation, not merely a stale cleanup read. The shown effects are refcount underflow, kernel corruption, and plausible crash. Useful reclaim, directed corruption, or privilege escalation remains unproven. It is CLASS_B rather than CLASS_A. ImportantCandidate is YES because a remotely influenced active-object UAF performs concrete post-free refcount mutations whose non-crash leverage remains unresolved. Auto-downgrade is disallowed for the same reason. No authorization decision is modified, so B4-PENDING does not apply. 5. One-sentence report phrase An SCTP timer-cleanup race can free an association or transport before the timer handler performs stale hold/put refcount mutations, producing a real active-object UAF with underflow and crash or corruption potential. 6. Manual review advice MANUAL CHECK REQUIRED Review remote control over association teardown, allocator reuse between cleanup and stale refcount mutation, and whether the underflow can affect a reclaimed object. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: sctp: hold asoc or transport before mod_timer() in timer handlers [ Upstream Commit: f7dea7eaea20fe9b80f8f77ba44d02b4a17f8050 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f7dea7eaea20fe9b80f8f77ba44d02b4a17f8050 Changed files: net/sctp/input.c net/sctp/sm_sideeffect.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=f7dea7eaea20fe9b80f8f77ba44d02b4a17f8050 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98586 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98586 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:N/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: IMPORTANT KPANIC detected for this report: NO Published priority for this report (same as in Subject): IMPORTANT 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).