From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99112][MODERATE REGULAR] net/sched: cls_flower: validate mask pointer after nla_next() Date: Fri, 30 Oct 2026 11:47:02 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99112 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: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 45e60747a9db2307929260d9aa9c1c6cbb70ee77 List-Id: CVE: CVE-2026-99112 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: net/sched: cls_flower: validate mask pointer after nla_next() Commit: 45e60747a9db2307929260d9aa9c1c6cbb70ee77 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=45e60747a9db2307929260d9aa9c1c6cbb70ee77 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99112 Analysis date: Fri, 30 Oct 2026 11:47:02 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: A CAP_NET_ADMIN-gated malformed cls_flower tunnel mask can cause a confirmed slab out-of-bounds read and possible kernel crash, without a shown disclosure or write primitive. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99112 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99112 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-99112 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99112 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H';CWE-125;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.1';DESCR 'A malformed cls_flower tunnel option mask can leave the mask cursor on incomplete trailing bytes or beyond the mask payload after nla_next. The next tunnel option helper can call nla_type and nla_parse_nested_deprecated with this unchecked pointer, causing a confirmed slab out of bounds read in __nla_validate_parse and potentially a kernel crash. For the CVSS the PR:L value is selected because reliable triggering requires local access to traffic control configuration with CAP_NET_ADMIN, which may be delegated inside a network namespace and does not necessarily represent full host administration. The base impact is availability loss without proven disclosure or modification, while the paranoid score reserves limited confidentiality impact because adjacent slab data is consumed as parser metadata. The issue is not directly triggered by ordinary remote packet traffic. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 6.1 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage IMPORTANT to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE REMOTE READ KASAN OOB LEAK NETWORK LINUS LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 2. * Conservative score: 2; no floor or cap applied. * Raw paranoid score: 2. * Paranoid score: 2; confidentiality was not added because no disclosure path is shown. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 weak/indirect corruption candidate: malformed nested mask attributes advance `nla_opt_msk` beyond the valid mask payload, producing a confirmed slab out-of-bounds read in `__nla_validate_parse()`. * +1 reliable kernel crash/strong DoS: the invalid parser walk plausibly causes an Oops or kernel crash. * No OOB-write or lifetime-corruption points: the evidence shows reads through `nla_type()` and nested parsing, not a write. Therefore NEW52/B5-R does not apply. * No confidentiality point: adjacent slab bytes are consumed internally as parser metadata, but no bytes are shown reaching userspace, packets, or another observable output. * No extra availability point: it would duplicate the same possible crash. * No privilege penalty: host-admin-equivalent privilege is not positively established. * No local-unprivileged bonus: the complete below-host-admin/net-namespace trigger is not positively established. * No remote bonus: ordinary network packets do not configure cls_flower attributes. 3. Reachability analysis The trigger is a malformed traffic-control netlink configuration using cls_flower tunnel-option key and mask attributes. CAP_NET_ADMIN is associated with this operation, but the supplied evidence only says it may be delegated in a network namespace; it does not prove that every required device, qdisc, filter, and tunnel-option stage is available in an attacker-created namespace. Accordingly, both effective host-admin and complete namespace-scoped reachability remain unknown. Numeric host UID 0 is not inherently required because capability-bearing non-root processes can issue traffic-control requests. No special hardware, boot option, race, or remote packet sequence is required. An attacker with the necessary traffic-control authority can instantiate the malformed filter directly. 4. Primitive and severity reading The exact primitive is an attacker-shaped, read-only slab out-of-bounds parser walk caused by validating the old mask cursor but not the cursor produced by `nla_next()`. It is neither a UAF nor an active-state write. The shown consequence is invalid kernel memory consumption and plausible crash; disclosure, state modification, arbitrary access, and privilege escalation are unproven. This is CLASS_C rather than CLASS_A/B. ImportantCandidate is NO because there is no write, lifetime violation, authorization bypass, shared-backing modification, or demonstrated trust-boundary corruption. Auto-downgrade is allowed, although manual confirmation of namespace reachability and any observable parser output is recommended. 5. One-sentence report phrase A CAP_NET_ADMIN-gated malformed cls_flower tunnel mask can cause a confirmed slab out-of-bounds read and possible kernel crash, without a shown disclosure or write primitive. 6. Manual review advice MANUAL CHECK RECOMMENDED Confirm whether the complete trigger works with attacker-obtainable namespace-scoped CAP_NET_ADMIN and whether any parser result can become externally observable. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: cls_flower: validate mask pointer after nla_next() Commit: 45e60747a9db2307929260d9aa9c1c6cbb70ee77 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=45e60747a9db2307929260d9aa9c1c6cbb70ee77 Commit description: fl_set_enc_opt() iterates the key's nested tunnel-option attributes with nla_for_each_attr() while advancing a single mask pointer via nla_next() at the bottom of each loop, so the mask cursor is driven by the number of key attributes rather than by the mask's own attributes. The nla_ok() added by commit c96adff ("cls_flower: call nla_ok() before nla_next()") only validates the mask pointer that was just consumed; the pointer produced by nla_next() is used by the next iteration (fl_set_geneve_opt() and siblings) without any validation. The mask's nested attributes are validated with NL_VALIDATE_LIBERAL, which merely warns on trailing bytes that do not form a complete attribute. A mask carrying one valid attribute plus 1-3 residue bytes (or a non-aligned attribute length making msk_depth negative) therefore reaches the next iteration with msk_depth != 0, so neither the !msk_depth check in fl_set_enc_opt() nor the !depth check in the per-type helpers fires. nla_type() then reads past the mask payload and nla_parse_nested_deprecated() iterates with an nla_len taken from those bytes, reading well beyond the mask attribute (KASAN: slab-out-of-bounds read in __nla_validate_parse from fl_change()). Validate the advanced mask pointer as well: when the mask is not legitimately exhausted (msk_depth != 0) and the new pointer fails nla_ok(), reject the filter with -EINVAL. An exactly exhausted mask still skips the check, preserving exact-match behaviour for the remaining key attributes. Fixes: c96adff ("cls_flower: call nla_ok() before nla_next()") Reported-by: TencentOS Corvus AI Cc: stable@vger.kernel.org Signed-off-by: Aohan Mei Link: https://patch.msgid.link/20260826025123.62758-1-ljp1205831794@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/sched/cls_flower.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=45e60747a9db2307929260d9aa9c1c6cbb70ee77 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99112 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99112 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:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H The Best / paranoid CVSS score: 6.1 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: 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: 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).