From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-90088][MODERATE REGULAR] Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop [ Upstream Date: Fri, 18 Sep 2026 03:01:06 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-90088 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 3 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: e7c0aa45ae6c5a338661b23812bfcdef50bf3e96 List-Id: CVE: CVE-2026-90088 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop [ Upstream Commit: e7c0aa45ae6c5a338661b23812bfcdef50bf3e96 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e7c0aa45ae6c5a338661b23812bfcdef50bf3e96 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90088 Analysis date: Fri, 18 Sep 2026 03:01:06 -0400 ActionableScore: 3 ActionableScore lower bound: unknown Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90088 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90088 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 REGULAR 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-2026-90088 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90088 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-835;**CWE-400;*CWE-20;BEST CVSS score: '6.5';DESCR 'A Bluetooth RFCOMM peer can provide a zero MTU in a PN frame, causing the affected DLC to retain an invalid fragmentation size. When the local endpoint later sends data, the sendmsg path repeatedly creates zero length fragments because the remaining length never decreases. This can continuously allocate skbs until system memory is exhausted, resulting in OOM activity, severe loss of responsiveness, or a system wide denial of service. For the CVSS the PR:N value is used because a remote peer may trigger the vulnerable state without privileges on the target when the RFCOMM endpoint accepts the connection. The attack is adjacent rather than Internet remote because it normally requires Bluetooth radio proximity and access to an RFCOMM session. Impact is availability only because the code shows uncontrolled allocation and an infinite loop but no UAF, out of bounds access, information leak, or write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) SKIP CVE-2026-90088 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE REMOTE INIT SIMPLEFIX NETWORK MEMORY DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 3 * Conservative score: 3 * Raw paranoid score: 3 * Paranoid score: 3 * No floor or cap was applied. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown * +2 Remote reachable. An RFCOMM peer directly supplies the zero MTU through a PN frame. Exploitation is Bluetooth-adjacent rather than Internet-routable. * +1 Reliable strong DoS. Once the affected local endpoint sends data, fragmentation makes no progress and continuously allocates zero-length skbs until memory exhaustion or OOM disruption. * No additional Availability point. System memory exhaustion is the same demonstrated DoS consequence, not an independent persistent effect. * No resource-leak point. The defect causes an active unbounded allocation loop rather than a permanently lost reference from normal cleanup. * No UAF, OOB access, overwrite, disclosure, authorization bypass, or ownership violation is established. * Controlled corruption, arbitrary write, confidentiality impact, integrity impact, and privilege escalation are not demonstrated. * No rare-hardware penalty. Bluetooth access is required, but the evidence does not establish uncommon physical hardware. * No race penalty. The failure follows a deterministic protocol and send sequence. 3. Reachability analysis A remote Bluetooth peer can negotiate MTU zero when it can establish or influence an RFCOMM session. The victim endpoint must subsequently send nonempty data, but this may occur during ordinary service operation and does not require attacker-controlled timing. The attacker requires Bluetooth radio proximity or equivalent access to the Bluetooth transport, not local execution or host-administrator privilege. Pairing and profile authorization may restrict exposure in particular deployments, but they are not established as mandatory by the supplied evidence. No namespace capability, boot option, special sysctl, or rare device prerequisite is shown. An exposed RFCOMM endpoint is the primary deployment prerequisite. 4. Primitive and severity interpretation The exact primitive is attacker-controlled assignment of zero to an active RFCOMM DLC MTU, followed by a non-progressing fragmentation loop that repeatedly allocates skbs. This is a deterministic resource-exhaustion and DoS condition, not memory corruption or a lifetime violation. PrimitiveClass is CLASS_C because the demonstrated behavior is host resource exhaustion without an independently useful corruption primitive. ImportantCandidate is NO because there is no UAF, controlled overwrite, security-boundary bypass, or exploitation leverage beyond availability loss. AutoDowngradeAllowed is YES because no unresolved corruption or ownership primitive would be discarded, although the adjacent remote trigger justifies review rather than immediate dismissal. The likely operational severity is Moderate for systems exposing RFCOMM services to untrusted nearby peers. 5. One-sentence report phrase A nearby Bluetooth RFCOMM peer can negotiate a zero MTU and cause the send path to allocate zero-length skbs indefinitely, resulting in system memory exhaustion and denial of service when the affected endpoint transmits data. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Confirm whether the product enables and exposes RFCOMM services to untrusted Bluetooth peers and whether pairing or profile authorization prevents the trigger. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop [ Upstream Commit: e7c0aa45ae6c5a338661b23812bfcdef50bf3e96 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e7c0aa45ae6c5a338661b23812bfcdef50bf3e96 Changed files: net/bluetooth/rfcomm/core.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=e7c0aa45ae6c5a338661b23812bfcdef50bf3e96 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90088 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90088 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: Not available The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 6.5 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: 3 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: NO Published priority for this report (same as in Subject): MODERATE REGULAR 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).