From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74688][MODERATE 7.0] sctp: clear control chunk transport if it is being removed [ Upstream Date: Sat, 22 Aug 2026 17:14:25 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74688 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: dbb3f418a8665ffb0514e1a9520ab6a1c5d4d886 List-Id: CVE: CVE-2026-74688 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: sctp: clear control chunk transport if it is being removed [ Upstream Commit: dbb3f418a8665ffb0514e1a9520ab6a1c5d4d886 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dbb3f418a8665ffb0514e1a9520ab6a1c5d4d886 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74688 Analysis date: Sat, 22 Aug 2026 17:14:25 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate at minimum / Strong Important candidate for manual review Manual review required: YES Summary: An SCTP peer may trigger a stale `chunk->transport` use-after-free when a queued control chunk survives peer transport removal, causing at least a remote kernel crash and requiring manual review due to network-reachable kernel lifetime corruption. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74688 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74688 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-2026-74688 MODERATE 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-664;CWE-362;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.1';DESCR 'An SCTP use after free can occur when sctp_make_heartbeat_ack caches a peer transport pointer in a control chunk without taking a reference. If src_out_of_asoc_ok keeps the HEARTBEAT ACK queued and the peer transport is removed before that queued control chunk is sent, the chunk can retain a stale transport pointer and later dereference freed memory during transmission. For the CVSS the PR:N is used because a network peer can potentially trigger the affected SCTP association state without local code execution on the victim when SCTP is reachable. The issue is network reachable over SCTP, but reliable triggering depends on specific ASCONF and HEARTBEAT timing and therefore AC:H is appropriate. Impact is at least remote denial of service via kernel crash and for the paranoid score may include confidentiality and integrity impact because the primitive is a stale pointer use after free in kernel networking memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum / Strong Important candidate for manual review (with actual score 5) YES UAF NETWORK LINUS KPANIC KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: **4** * Paranoid score: **5** * Final recommended bucket: **Actionable Moderate at minimum / Strong Important candidate for manual review** ## 2. Signal breakdown * **Remote reachable / network-triggerable: +2** SCTP is a network protocol path, and the stale `chunk->transport` can be reached by peer-driven SCTP association state when SCTP is exposed. * **Memory corruption, weak primitive: +1** The patch and commit explicitly describe a stale pointer and use-after-free, but there is no demonstrated attacker-controlled reclaim, overwrite, callback control, type confusion, or refcount takeover. * **Real lifetime corruption: +1** `chunk->transport` is cached without a reference, the peer transport is removed and scheduled for RCU freeing, and the queued control chunk can later dereference the freed transport. * **Reliable kernel crash / strong DoS: +1** A stale transport pointer dereference in kernel networking code can realistically crash the kernel. * **Hard or unreliable race / special state required: -1** Triggering depends on a specific SCTP state sequence involving `src_out_of_asoc_ok`, queued `HEARTBEAT ACK`, peer transport removal, and later `ASCONF_ACK` clearing suppression. * **Paranoid uplift to 5** Because this is a network-reachable kernel UAF in protocol code, manual-review sensitivity justifies treating it as Actionable Moderate at minimum, even though the demonstrated primitive is weaker than a reclaimable UAF. ## 3. Reachability analysis A remote SCTP peer may be able to influence the affected association state if SCTP is enabled and reachable. No local code execution on the victim is required in that model, so PR is effectively none for network exposure. The path is not as broadly exposed as TCP or UDP, and many systems do not expose SCTP services by default. Realistic exploitation requires a specific protocol sequence and timing around queued control chunks and transport removal, so exploitability is non-trivial. Namespaces and containers mainly matter if SCTP exposure is delegated through network namespaces or containerized services. The main practical risk is to hosts or appliances that expose SCTP to untrusted peers. ## 4. Severity interpretation This is more than an ordinary Moderate because the patch fixes a real stale-pointer lifetime bug in a network protocol path. Conservative handling should treat it as a remote DoS with weak UAF primitive. Theoretical memory corruption potential exists because the stale object is freed under RCU and later dereferenced, but the supplied patch does not show attacker-controlled reclaim or a write primitive. Therefore it should not be scored as proven privilege escalation, but it should not be auto-closed. ## 5. One-sentence report phrase An SCTP peer may trigger a stale `chunk->transport` use-after-free when a queued control chunk survives peer transport removal, causing at least a remote kernel crash and requiring manual review due to network-reachable kernel lifetime corruption. ## 6. Manual review recommendation **MANUAL CHECK REQUIRED** Reason: network-reachable kernel UAF candidates historically need manual review even when the demonstrated impact is only DoS, because exploitability depends on object lifetime, RCU reuse behavior, and protocol-state controllability. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: sctp: clear control chunk transport if it is being removed [ Upstream Commit: dbb3f418a8665ffb0514e1a9520ab6a1c5d4d886 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dbb3f418a8665ffb0514e1a9520ab6a1c5d4d886 Changed files: net/sctp/associola.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=dbb3f418a8665ffb0514e1a9520ab6a1c5d4d886 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74688 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74688 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:N/I:N/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: 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).