From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74714][MODERATE 7.0] bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch() [ Upstream Date: Sat, 22 Aug 2026 15:07:04 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74714 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: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: cc0295f89296ed351fc4b0b48fee887ba02c5d24 List-Id: CVE: CVE-2026-74714 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch() [ Upstream Commit: cc0295f89296ed351fc4b0b48fee887ba02c5d24 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cc0295f89296ed351fc4b0b48fee887ba02c5d24 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74714 Analysis date: Sat, 22 Aug 2026 15:07:04 -0400 ActionableScore: 6 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A race in bpf_iter_tcp_established_batch can take a reference on a TCP_NEW_SYN_RECV request_sock while its refcount is still zero, causing refcount corruption and a use-after-free that is locally triggerable through BPF TCP iterator reads plus TCP connection churn. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74714 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74714 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-2026-74714 MODERATE 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:H/I:H/A:H';*CWE-416;CWE-362;CWE-911;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 bpf_iter_tcp_established_batch can corrupt the reference count of a TCP_NEW_SYN_RECV request_sock because the iterator used sock_hold on a socket that can be visible in the ehash table with sk_refcnt equal to 0. The lost iterator reference can leave the request_sock one reference short and allow it to be freed while still reachable, creating a use after free condition. For the CVSS the PR:L is used because reliable triggering requires a local user or process that can read a BPF TCP iterator while creating TCP connection churn. The issue is not directly network reachable by packet traffic alone, although TCP connection activity is part of the race. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality and integrity impact due to use after free memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES REMOTE BPF UAF NETWORK HARDWARE KPANIC INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 6 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown * Generic memory corruption, strong corruption primitive: +2 Explicit use-after-free is described. The request_sock can be freed while still reachable due to refcount corruption. * Real lifetime corruption: +1 This is a refcount lifetime bug involving sock_hold on an object with sk_refcnt equal to 0 and later refcount_set clobbering the iterator reference. * Reliable kernel crash / strong DoS: +1 The commit shows refcount_t warning and states the reproducer works in seconds with tcp_syncookies=0 and concurrent connect close plus iter tcp reads. * Weak to moderate LPE concern: +1 UAF plus refcount abuse in TCP socket lifetime handling is enough for manual review, but no attacker controlled reclaim, type confusion, callback control, or arbitrary write is shown. * Common networking core path or packet-processing adjacency: +1 The affected object is TCP_NEW_SYN_RECV request_sock in the TCP ehash path, although the vulnerable reader is the BPF TCP iterator rather than ordinary packet processing alone. * Requires admin/root/CAP_* in typical BPF deployments: -2 Creating or attaching BPF iterators is normally gated by CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN, or root controlled policy. If an already created iter tcp link is readable by a less privileged local user, the practical reachability becomes worse. * Paranoid adjustment: +1 If a lower privileged local process can read an exposed iter tcp link while generating TCP churn, the issue becomes an actionable local UAF despite BPF setup being privileged. BPF gating keeps the paranoid score capped at 6 absent a demonstrated reclaim or LPE exploit. ## 3. Reachability analysis The bug is not directly remote reachable by network packets alone. TCP connection churn is part of the race, but a local process must read the BPF TCP iterator at the same time. In conservative product configurations where unprivileged BPF is disabled, the vulnerable iterator setup requires privileged BPF access, so the issue is privileged local. In a less restrictive deployment, or if a privileged service exposes an iter tcp link with readable permissions, a local lower privileged user could plausibly trigger it by combining iterator reads with local TCP connect close churn. The path is not a default ordinary syscall path for all users because it depends on BPF iterator availability. The race is not merely theoretical because the commit says it reproduces in seconds under the stated conditions. Call-site confidence: high. The patch and commit show the affected function, the refcount misuse, the race sequence, and the corrected refcount_inc_not_zero behavior. ## 4. Severity interpretation This is above an ordinary Moderate because the bug is an explicit refcount lifetime error leading to UAF in TCP socket handling. Realistic demonstrated impact is local kernel crash or warning driven DoS. Practical privilege escalation is not demonstrated, but the UAF plus refcount corruption makes it unsafe to auto-close without manual review. Conservative interpretation is Actionable Moderate. Paranoid interpretation reaches the upper Actionable Moderate range because a local lower privileged trigger may exist when an iter tcp link is exposed, but the BPF privilege gate and lack of controlled reclaim keep it below a high-end Important score. ## 5. One-sentence report phrase A race in bpf_iter_tcp_established_batch can take a reference on a TCP_NEW_SYN_RECV request_sock while its refcount is still zero, causing refcount corruption and a use-after-free that is locally triggerable through BPF TCP iterator reads plus TCP connection churn. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: explicit UAF, refcount lifetime corruption, reproducible race, and possible local privilege escalation concern despite BPF privilege gating. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch() [ Upstream Commit: cc0295f89296ed351fc4b0b48fee887ba02c5d24 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cc0295f89296ed351fc4b0b48fee887ba02c5d24 Changed files: lib/refcount.c net/ipv4/tcp_ipv4.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=cc0295f89296ed351fc4b0b48fee887ba02c5d24 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74714 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74714 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: 5 Paranoid ActionableScore: 6 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).