From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-90335][LOW] tty: skip cdev_del() when no cdev is registered [ Upstream Date: Thu, 17 Sep 2026 16:55:39 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-90335 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 3dbf85ef40b6366ba15e882f7536cdc98bea579a List-Id: CVE: CVE-2026-90335 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: tty: skip cdev_del() when no cdev is registered [ Upstream Commit: 3dbf85ef40b6366ba15e882f7536cdc98bea579a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3dbf85ef40b6366ba15e882f7536cdc98bea579a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90335 Analysis date: Thu, 17 Sep 2026 16:55:39 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90335 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90335 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: LOW Manual review required: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-90335 LOW https://www.kernelcve.org/list/?q=CVE-2026-90335 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-703;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A NULL pointer dereference can occur in tty_unregister_device because cdev_del() may be called with a NULL cdev slot after TTY device registration failed before a cdev was allocated. The serial core may keep the port available for later operations, and a later device removal can reach the unregister path with driver cdevs index still NULL. For the CVSS the PR:L is used in the paranoid score because some environments may delegate device management, reset, bind, or unbind operations to a local service or reduced capability root context. The typical practical trigger still requires local control over the TTY device lifecycle or a driver error path during registration and removal. The issue is not network reachable. Impact is denial of service via kernel crash, with no clear UAF, OOB access, information disclosure, or privilege escalation primitive indicated by the code change.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES PRINTF-TTY SIMPLEFIX HARDWARE LINUS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2 * Raw paranoid score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate**:: No floor or cap changed the score. 2. Signal breakdown Positive signals: * +1: Invalid object pointer / NULL pointer dereference path. tty_unregister_device() can pass a NULL driver->cdevs[index] pointer to cdev_del(). * +1: Reliable kernel crash / DoS. The commit explicitly states that the NULL cdev slot causes a NULL-pointer dereference. Negative signals: * 0: No host-admin penalty applied because host-admin-equivalent privilege is likely in practical device lifecycle scenarios, but not fully proven by the supplied evidence. * 0: No race penalty. This is an ordered error/lifecycle state issue, not a timing race. * 0: No rare hardware penalty. TTY/serial is common enough, and the patch does not establish a rare physical-only prerequisite. Important non-awarded signals: * RealUAF not awarded. The bug is a NULL pointer dereference, not post-free use. * Concrete repeated release/refcount not awarded. There is no first release that may end lifetime followed by a second lifetime mutation on the same dangling reference. * Structured stale-object leverage not awarded. No stale active object reuse or attacker-shaped replacement is shown. * Weak LPE not awarded. The patch supports crash-only behavior. * Controlled reclaim not demonstrated. * Arbitrary write not demonstrated. * Confidentiality and integrity not awarded. * Remote reachability not established. * Extra availability point not awarded because the same kernel crash is already counted once. 3. Reachability analysis The vulnerable path is inside TTY device unregister handling after an earlier TTY device registration failure before cdev allocation. A realistic trigger likely requires local influence over device registration and later removal, such as driver/device lifecycle control, bind/unbind, reset, or a failing serial/TTY registration path. The supplied evidence does not prove that an ordinary unprivileged user can complete the trigger. It also does not prove that host-admin-equivalent privilege is strictly required in all cases. Therefore HostAdminRequired is UNKNOWN rather than YES or NO. No namespace-scoped privilege path is established. This is not a network-triggered issue. No prior special sysctl, boot option, or rare hardware prerequisite is established from the supplied input. This is not a race, so race repeatability is not relevant. 4. Primitive and severity interpretation The exact primitive is a NULL pointer dereference in tty_unregister_device() when driver->cdevs[index] is NULL but cdev_del() is still called. This is not an active structured UAF and not fixed stale storage. It is a crash-oriented invalid-state bug in an unregister path. The demonstrated consequence is kernel crash / denial of service. The speculative consequence does not extend to privilege escalation because no UAF, OOB access, controlled write, object replacement, refcount takeover, callback control, disclosure, or authorization bypass is indicated. PrimitiveClass is CLASS_C because the established behavior is invalid dereference / DoS-only. ImportantCandidate is NO because there is no meaningful unresolved exploitation primitive beyond crash. AutoDowngradeAllowed is YES because the issue appears suitable for ordinary Moderate / Low-like handling and does not preserve an Important-grade primitive. 5. One-sentence report phrase A failed TTY device registration can leave a NULL cdev slot that is later passed to cdev_del() during unregister, causing a local kernel crash and denial of service without evidence of UAF, information disclosure, or privilege escalation. 6. Manual review recommendation NO MANUAL CHECK NEEDED Reason: crash-only NULL pointer dereference, no memory corruption primitive, no authorization bypass, no network reachability, and no evidence of LPE. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: tty: skip cdev_del() when no cdev is registered [ Upstream Commit: 3dbf85ef40b6366ba15e882f7536cdc98bea579a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3dbf85ef40b6366ba15e882f7536cdc98bea579a Changed files: drivers/tty/tty_io.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=3dbf85ef40b6366ba15e882f7536cdc98bea579a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90335 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90335 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:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.7 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: unknown Paranoid ActionableScore: 2 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).