From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99282][MODERATE 7.0] net/sched: sch_teql: fix use-after-free on lower qdisc drop Date: Sat, 07 Nov 2026 22:08:15 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99282 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: unknown X-AL-KERNEL-Commit: fc55d92ae6a4b2e7d062cad6d4c67f6b061d9cde List-Id: CVE: CVE-2026-99282 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: net/sched: sch_teql: fix use-after-free on lower qdisc drop Commit: fc55d92ae6a4b2e7d062cad6d4c67f6b061d9cde Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fc55d92ae6a4b2e7d062cad6d4c67f6b061d9cde Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99282 Analysis date: Sat, 07 Nov 2026 22:08:15 -0400 ActionableScore: 5 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: A lower qdisc can free an skb while TEQL still writes and adjusts that stale skb, producing a repeatable kernel UAF with unresolved post-free corruption leverage. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99282 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99282 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-2026-99282 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99282 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 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:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-672;CWE-670;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'sch_teql treated every ndo_start_xmit result other than NETDEV_TX_OK as if the skb had not been consumed. A VLAN slave can propagate NET_XMIT_DROP after the lower qdisc has already freed the skb, after which teql_master_xmit writes skb dev and calls __skb_pull on freed memory. This provides a concrete use after free access and can cause a kernel crash. Reallocation of the freed skb before these writes may also corrupt another object, so privilege escalation cannot be excluded even though no arbitrary write primitive is proven. For the CVSS the PR:L value assumes a local user or process can generate traffic through an existing vulnerable TEQL and VLAN configuration. Creating the required qdisc topology normally requires CAP_NET_ADMIN. Direct remote reachability is not established and the specific network configuration raises attack complexity. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because FD false positive review allowed a downgrade. 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 produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH. The independent weaker Aegis shadow evaluated CVSS 1.9 and ActionableScore 1 with primitive class CLASS_B 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 5) MAYBE REMOTE LOCK LEAK UAF NETWORK SKB TEST QDISC KPANIC PACKET DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 5. * Conservative score: 5; no floor or cap changed the arithmetic. * Raw paranoid score: 5. * Paranoid score: 5; allocator reuse was not independently proven, so no speculative extra point. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 real UAF: the lower qdisc frees the consumed skb after returning `NET_XMIT_DROP`, but TEQL retains and uses that stale pointer. * +1 weak exploitation leverage: TEQL performs concrete post-free mutations, restoring `skb->dev` and applying `__skb_pull()` to freed structured storage. This is stronger than a read-only stale dereference, but target selection or controlled reclaim is not shown. * +1 reliable kernel crash/strong DoS: writes and pointer arithmetic through a freed skb plausibly cause an Oops or kernel crash. * +1 attacker-influenced repeatable lifetime sequence: after the demonstrated topology exists, packet transmission repeatedly induces lower-qdisc consumption followed by TEQL’s stale use. * No extra availability point: it would duplicate the same crash. * No Class A, arbitrary write, controlled reclaim, disclosure, LPE, or attacker-shaped replacement object is shown. * No repeated release/refcount operation exists; the bug is post-free access rather than a second `put` or `free`. * B4-PENDING does not apply: there is no authorization DENY-to-ALLOW defect. 3. Reachability analysis The demonstrated trigger needs TEQL, VLAN, dummy, and a dropping lower qdisc. Creating that topology normally requires CAP_NET_ADMIN, while a local process may exercise an already configured path by sending traffic. The evidence does not establish whether one below-host-admin actor can create the complete topology, nor whether all required capability checks are usable in attacker-created user/net namespaces. Therefore both host-admin and namespace-scoped privilege remain unknown. No hard-race penalty applies: the shown drop/return/use sequence is deterministic once configured. 4. Primitive and severity reading This is an active structured-object UAF with concrete writes after the skb lifetime ends, not fixed stale storage or cleanup-only dereference. Later corruption of a reallocated object is credible but unproven. The explicit post-free mutations leave material exploit leverage unresolved, supporting CLASS_B, mandatory Important-vs-Moderate review, and prohibiting automatic downgrade. Likely operations severity is actionable Moderate unless further analysis demonstrates reclaim control or a stronger cross-boundary effect. 5. One-sentence report phrase A lower qdisc can free an skb while TEQL still writes and adjusts that stale skb, producing a repeatable kernel UAF with unresolved post-free corruption leverage. 6. Manual review advice MANUAL CHECK REQUIRED Review allocator reuse, exact `__skb_pull()` mutations, namespace capability scope, and whether ordinary users can drive traffic through a preconfigured vulnerable topology. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/sched: sch_teql: fix use-after-free on lower qdisc drop Commit: fc55d92ae6a4b2e7d062cad6d4c67f6b061d9cde Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fc55d92ae6a4b2e7d062cad6d4c67f6b061d9cde Commit description: The issue: teql_master_xmit() tests the slave's ndo_start_xmit() return value against NETDEV_TX_OK alone. A slave that consumes the skb but returns an error code (rc < NET_XMIT_MASK, e.g. NET_XMIT_DROP) is treated as if the skb were still owned, so the loop restores skb->dev and calls __skb_pull() on it. A VLAN slave returns the result of dev_queue_xmit() from its ndo_start_xmit() (propagated since cbbef5e ), and when the lower qdisc drops the packet that value is NET_XMIT_DROP after the skb has been freed, giving a use-after-free in teql_master_xmit(). The Fix: test for consumption with dev_xmit_complete(), which accepts NETDEV_TX_OK and every rc < NET_XMIT_MASK, matching other callers that need to distinguish consumed results from busy. Only NETDEV_TX_OK keeps the packet counted in tx_packets/tx_bytes and advances the slave; a consumed result that is neither a success nor NET_XMIT_CN ends the attempt and is charged to tx_dropped, so lower-qdisc drops are no longer reported as good transmits. NET_XMIT_CN is counted like success because it can accompany acceptance of the current packet: pfifo_head_drop drops the old head, enqueues the current skb and returns NET_XMIT_CN. Conditions to recreate the bug: With CONFIG_NET_SCH_TEQL, CONFIG_VLAN_8021Q and CONFIG_DUMMY enabled, add lkrdummy0 (dummy) and lkrvlan0 (VLAN id 37 on lkrdummy0); set a pfifo limit 0 root on lkrdummy0 and a teql0 root on lkrvlan0; bring teql0 up with an address and send one UDP packet to it. The VLAN xmit returns NET_XMIT_DROP from the lower qdisc while holding a freed skb. Fixes: 572a9d7 ("net: allow to propagate errors through ->ndo_hard_start_xmit()") Link: https://lore.kernel.org/netdev/179248763469.3135.1739559328868319628@kernel.org/ Link: https://lore.kernel.org/netdev/20261023162821.GN708417@horms.kernel.org/ Cc: stable@vger.kernel.org Signed-off-by: owen kwan Signed-off-by: Jamal Hadi Salim Reviewed-by: Simon Horman Link: https://patch.msgid.link/QDISC-Y0BY.v2.r0.20261024060625-2@mojatatu.com Signed-off-by: Paolo Abeni Signed-off-by: Greg Kroah-Hartman Changed files: net/sched/sch_teql.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=fc55d92ae6a4b2e7d062cad6d4c67f6b061d9cde ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99282 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99282 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:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 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: 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).