From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99138][IMPORTANT] tcp: fix use-after-free in do_tcp_getsockopt(TCP_CC_INFO) Date: Wed, 28 Oct 2026 22:41:59 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99138 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 86814e5370068ec2bf0caa6e6d55c3e5bfc6c324 List-Id: CVE: CVE-2026-99138 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: NO Patch: tcp: fix use-after-free in do_tcp_getsockopt(TCP_CC_INFO) Commit: 86814e5370068ec2bf0caa6e6d55c3e5bfc6c324 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=86814e5370068ec2bf0caa6e6d55c3e5bfc6c324 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99138 Analysis date: Wed, 28 Oct 2026 22:41:59 -0400 ActionableScore: 4 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: A concurrent BPF congestion-control unregister can leave `TCP_CC_INFO` processing calling through a stale `icsk_ca_ops` object, causing a real kernel UAF with unresolved callback-reuse leverage. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99138 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99138 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: IMPORTANT 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-2026-99138 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-99138 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT IMPORTANT AEGIS_AS=6 LEGACY=IMPORTANT RESULT=SAME INDEPENDENT_LEGACY=MODERATE_KPANIC INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_HARD_VETO PRE_MERGE_LEGACY=MODERATE_KPANIC (final reconciliation agrees; DECISION: both IMPORTANT) 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-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in do_tcp_getsockopt for TCP_CC_INFO can read a BPF struct_ops congestion control object after it has been freed and can then dereference or call its stale get_info function pointer. A local process can repeatedly query TCP_CC_INFO on a socket, but the lifetime transition requires the BPF congestion control object to be replaced or unregistered concurrently and reliable control may depend on delegated BPF or network administration capabilities. For the CVSS the PR:L value reflects required local code execution and practical influence over the affected socket or congestion control lifecycle. AC:H reflects the need to hit a concurrent free window. Impact is at least a local denial of service and the stale indirect function call provides a plausible but unproven path to kernel code execution or privilege escalation if freed memory reuse can be controlled. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7 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. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the manual review requirement was applied. final reconciliation stage MODERATE_KPANIC to IMPORTANT because a specific evidence based protection or manual review veto was applied and KP specialist did not establish a qualifying panic. 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. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK and TEMP_KPANIC_MERGE_IMPORTANT_VETO and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 6 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was IMPORTANT. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 4) MAYBE REMOTE READ LOCK BPF LEAK UAF NETWORK INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK TEMP_KPANIC_MERGE_IMPORTANT_VETO KPANIC_UNSUPPORTED_REMOVED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 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: 4. * Conservative score: 4. The real-UAF floor of 4 applies but does not change the score. * Raw paranoid score: 4. * Paranoid score: 4; no additional controlled-reclaim or privilege assumptions are justified. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 — Real active-object UAF: `icsk_ca_ops` can be freed while `do_tcp_getsockopt()` retains and uses the stale pointer. * +1 — Specific active structured use: the stale object’s `get_info` function pointer is read and potentially called. This is materially stronger than a shallow cleanup dereference, but is not controlled callback hijacking. * +1 — Plausible kernel crash/DoS: KASAN observed an eight-byte post-free read, and stale indirect-call processing can fault. * +0 — No race penalty: concurrency is required, but the evidence does not establish a narrow, one-shot, or externally uncontrollable race. * +0 — No local-unprivileged bonus: ordinary code can invoke `getsockopt(TCP_CC_INFO)`, but the complete trigger also needs concurrent BPF congestion-control replacement or unregister, whose privilege boundary is unresolved. * No controlled reclaim, attacker-shaped replacement, arbitrary write, disclosure, repeated refcount mutation, or proven LPE is shown. Confidentiality and integrity points are therefore withheld. * Extra availability is not counted separately from the same crash. * B4-PENDING does not apply; no authorization decision is changed from DENY to ALLOW. 3. Reachability analysis A local process can repeatedly query TCP congestion-control information on an affected socket. The freeing transition requires concurrent replacement or unregister of BPF `struct_ops` congestion control. The evidence does not establish whether one below-host-admin principal can perform both stages, whether delegated BPF/network capabilities suffice, or whether all required checks are namespace-scoped. The complete trigger is therefore potentially compound, with `HostAdminRequired` and namespace reachability unknown. No special hardware is required. 4. Primitive and severity reading This is an active structured-object UAF, not fixed stale storage or cleanup-only use. The stale path reads an ops member and may make an indirect call through `get_info`. That supports CLASS_B with meaningful unknown leverage past a simple crash, but not CLASS_A because reclaim, callback-target control, or another directed corruption primitive is absent. ImportantCandidate is YES because a concrete active-object UAF reaches an indirect function-pointer consumer and the BPF/delegated privilege boundary remains unresolved. Auto-downgrade is disallowed pending analysis of who controls unregister/replacement and whether freed ops storage or associated trampolines can be predictably reused. 5. One-sentence report phrase A concurrent BPF congestion-control unregister can leave `TCP_CC_INFO` processing calling through a stale `icsk_ca_ops` object, causing a real kernel UAF with unresolved callback-reuse leverage. 6. Manual review advice MANUAL CHECK REQUIRED Determine the complete BPF privilege model, race controllability, object/trampoline reclamation behavior, and whether one below-host-admin actor can drive both lifetime transition and stale callback invocation. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: tcp: fix use-after-free in do_tcp_getsockopt(TCP_CC_INFO) Commit: 86814e5370068ec2bf0caa6e6d55c3e5bfc6c324 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=86814e5370068ec2bf0caa6e6d55c3e5bfc6c324 Commit description: do_tcp_getsockopt() reads icsk->icsk_ca_ops and dereferences the get_info function pointer without rcu_read_lock(). With BPF struct_ops congestion control, ca_ops can point to dynamically allocated memory that is freed concurrently, resulting in a use-after-free when the kernel dereferences or calls through the stale pointer. BUG: KASAN: slab-use-after-free in do_tcp_getsockopt+0x2037/0x23e0 Read of size 8 at addr ffff888013701258 by task exploit/149 do_tcp_getsockopt+0x2037/0x23e0 (net/ipv4/tcp.c:4564) tcp_getsockopt+0x91/0xf0 __sys_getsockopt+0xf7/0x170 Fix this by wrapping the ca_ops load and get_info call within rcu_read_lock()/rcu_read_unlock(), and using READ_ONCE() to load the icsk_ca_ops pointer. Fixes: 0baf26b ("bpf: tcp: Support tcp_congestion_ops in bpf") Suggested-by: Eric Dumazet Cc: AutonomousCodeSecurity@microsoft.com Cc: stable@vger.kernel.org Reviewed-by: Eric Dumazet Signed-off-by: Cen Zhang (Microsoft Security FORGE Labs) Reviewed-by: Jiayuan Chen Reviewed-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/65fd3816ed5d541d9edd4bf4fcf97104a2cf907a.1787870710.git.blbllhy@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/ipv4/tcp.c net/ipv4/tcp_dctcp.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=86814e5370068ec2bf0caa6e6d55c3e5bfc6c324 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99138 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99138 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: 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: IMPORTANT KPANIC detected for this report: NO Published priority for this report (same as in Subject): IMPORTANT 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).