From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99191][MODERATE 7.0] calipso: keep BIG TCP payload_len in calipso_skbuff_setattr() [ Upstream Date: Wed, 28 Oct 2026 22:11:59 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99191 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: 4 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 1c9fcfca51e3c5cd46dd72a4da74d56eff183513 List-Id: CVE: CVE-2026-99191 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: calipso: keep BIG TCP payload_len in calipso_skbuff_setattr() [ Upstream Commit: 1c9fcfca51e3c5cd46dd72a4da74d56eff183513 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1c9fcfca51e3c5cd46dd72a4da74d56eff183513 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99191 Analysis date: Wed, 28 Oct 2026 22:11:59 -0400 ActionableScore: 4 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: Attacker-influenced forwarded IPv6 traffic can make CALIPSO replace the BIG TCP length marker with a wrapped length that privileged networking consumers subsequently trust. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99191 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99191 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-2026-99191 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99191 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L';CWE-190;CWE-682;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.8';DESCR 'CALIPSO updated the 16 bit IPv6 payload_len field by adding len_delta even when BIG TCP used payload_len 0 as a marker for obtaining the real length from skb len. This could replace the marker with a small incorrect value or wrap the field when the packet crossed IPV6_MAXPLEN. nf_tables, conntrack, and sch_cake rely on ipv6_payload_len, so attacker influenced forwarded traffic could be misclassified, truncated, dropped, or incorrectly accounted when CALIPSO labeling and BIG TCP or boundary crossing conditions are present. For the CVSS the PR:N value is selected because a network sender does not need a local account when its traffic reaches the configured forwarding and labeling path. AC:H reflects the required BIG TCP or size boundary condition and the uncommon CALIPSO and NetLabel configuration. No OOB access, UAF, arbitrary write, information leak, or demonstrated firewall bypass is established. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 4.8 and the production ActionableScore returned 4 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. 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 has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 4.8 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 4) MAYBE REMOTE LEAK NETWORK SKB DEBUGFS TEST IPV6 KPANIC PACKET - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 PrimitiveClass=CLASS_B RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 4. * Conservative score: 4; no floor or cap applied. * Raw paranoid score: 4. * Paranoid score: 4; no additional unsupported policy-bypass or memory-corruption effect added. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 remote/network trigger: an external sender can inject size-influenced IPv6 traffic into an already configured forwarding and CALIPSO-labeling path. * +1 active structured-state corruption: the code replaces BIG TCP’s `payload_len == 0` marker with a wrapped or truncated 16-bit value. * +1 privileged downstream consumption: `ipv6_payload_len()` and consumers including nf_tables, conntrack, and sch_cake subsequently trust the corrupted length. * +1 specific cross-boundary uncertainty: attacker-influenced packet metadata is rewritten by and consumed within the router’s more privileged network stack; policy/accounting consequences remain unresolved. * -1 uncommon, host-provisioned path: CALIPSO/NetLabel mapping and applicable forwarding configuration must already exist. * No OOB access, UAF, arbitrary write, checksum-placement write, protected-state change, firewall bypass, host crash, or confidentiality impact is shown. * NEW52 B5-R and NEW53 B3-PENDING do not apply: there is neither a retry-accumulated heap overwrite nor a shared-backing write. 3. Reachability analysis The triggering actor may be a remote sender without local privileges after an administrator has configured CALIPSO/NetLabel forwarding. That prior setup limits exposure but does not make each packet trigger host-admin-only. No namespace capability is involved or shown. BIG TCP or a payload-length boundary condition raises complexity, but no narrow timing race exists. 4. Primitive and severity reading The primitive is attacker-influenced corruption of an active IPv6 length field: zero means “derive the real BIG TCP length from the skb,” while the vulnerable arithmetic converts it into a misleading literal length. Later privileged packet-processing consumers use that value. This is CLASS_B semantic/structured-state corruption, not kernel-memory corruption. Packet truncation, drops, misclassification, and incorrect accounting are supported; authorization bypass, protected policy change, panic, and cross-host compromise are unproven. ImportantCandidate is YES under active-state/trust-boundary review, not because Important severity is proven. Auto-downgrade is disallowed until downstream netfilter/routing/accounting consequences are checked. 5. One-sentence report phrase Attacker-influenced forwarded IPv6 traffic can make CALIPSO replace the BIG TCP length marker with a wrapped length that privileged networking consumers subsequently trust. 6. Manual review advice MANUAL CHECK REQUIRED Review whether the incorrect length can alter netfilter, conntrack, routing, queueing, or namespace/host policy decisions beyond packet-local loss. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: calipso: keep BIG TCP payload_len in calipso_skbuff_setattr() [ Upstream Commit: 1c9fcfca51e3c5cd46dd72a4da74d56eff183513 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1c9fcfca51e3c5cd46dd72a4da74d56eff183513 Changed files: net/ipv6/calipso.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=1c9fcfca51e3c5cd46dd72a4da74d56eff183513 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99191 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99191 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:L The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L The Best / paranoid CVSS score: 4.8 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: 4 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).