From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74479][MODERATE REGULAR] net: pktgen: fix proc entry use-after-free Date: Sat, 15 Aug 2026 14:33:37 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74479 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: 4 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: 4ef801b838d85c0ea5852c50667f7344ce3b6cd0 List-Id: CVE: CVE-2026-74479 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: net: pktgen: fix proc entry use-after-free Commit: 4ef801b838d85c0ea5852c50667f7344ce3b6cd0 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4ef801b838d85c0ea5852c50667f7344ce3b6cd0 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74479 Analysis date: Sat, 15 Aug 2026 14:33:37 -0400 ActionableScore: 4 ActionableScore lower bound: 2 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A race between pktgen device rename and removal can pass a stale `proc_dir_entry` pointer to `proc_remove()`, causing a kernel use-after-free and likely local DoS, with limited but nonzero privilege-escalation concern in delegated CAP_NET_ADMIN environments. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74479 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74479 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74479 MODERATE CHECK WITH IMPACT FROM ORIG NN 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-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'pktgen has a race between NETDEV_CHANGENAME handling and kpktgend device removal where proc_remove can receive a stale proc_dir_entry pointer. The stale entry may already have been freed by the rename path, causing a slab use-after-free in proc_remove and a kernel crash. For the CVSS the PR:L is used in the paranoid score because reliable triggering may be possible for a local actor with delegated network administration or pktgen control rather than full host root in some deployments. The issue is not directly network reachable and is triggered through local pktgen and netdev control plane operations. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel use-after-free, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 3) YES REMOTE READ OOB DANGER RACE UAF HARDWARE LINUS DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 4 * Final recommended bucket: **Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * +1 Memory corruption, weak primitive: confirmed race-dependent slab use-after-free of `proc_dir_entry` in `proc_remove()`. * +1 Real lifetime corruption: stale procfs entry pointer can survive concurrent rename/removal. * +1 Reliable kernel crash / strong DoS: KASAN reports UAF in `proc_remove()`, and a normal kernel may crash or oops. * -1 Hard or unreliable race: triggering depends on timing between `NETDEV_CHANGENAME` and `kpktgend` removal. * -2 Requires admin/root/CAP_NET_ADMIN in typical deployments: pktgen and netdev rename/removal are normally privileged control-plane operations. Paranoid adjustments: * +1 Weak LPE concern: because this is a kernel heap UAF involving a procfs object passed into a removal/lifetime-management path, stale-object reuse should be manually reviewed, although no controlled reclaim or write primitive is demonstrated. * Privilege penalty is relaxed in the paranoid view because CAP_NET_ADMIN or pktgen control may be delegated to containers or reduced-capability service contexts and may not always mean full host root. Race-UAF downgrade applied: this is not treated as a strong corruption primitive because the patch does not show attacker-controlled reclaim, write-after-free, type confusion, callback control, or refcount takeover. ## 3. Reachability analysis The bug is locally triggerable through pktgen and netdev control-plane operations, not through incoming network traffic. In typical deployments, writing to pktgen control interfaces and renaming/removing network devices requires root or CAP_NET_ADMIN, so the conservative score is low. In containerized or delegated network-administration environments, the effective privilege may be closer to PR:L because a reduced-capability actor may control network devices or pktgen without being full host root. pktgen is not a common default data-plane path and is mostly a testing or traffic-generation facility, which limits exposure. Call-site confidence: high, because the patch directly shows `proc_remove(pkt_dev->entry)` being moved under `if_lock()` and the commit provides the exact racing call paths. ## 4. Severity interpretation This behaves more like a borderline but actionable Moderate than a clear Important issue. The realistic demonstrated impact is local DoS via kernel crash. The theoretical concern is higher because the primitive is a real kernel heap use-after-free, but there is no evidence in the patch of controlled object replacement, arbitrary write, callback hijack, or reliable privilege escalation. Manual review is still required because early triage should not auto-close confirmed kernel UAF races. ## 5. One-sentence report phrase A race between pktgen device rename and removal can pass a stale `proc_dir_entry` pointer to `proc_remove()`, causing a kernel use-after-free and likely local DoS, with limited but nonzero privilege-escalation concern in delegated CAP_NET_ADMIN environments. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: confirmed kernel heap use-after-free in a lifetime-management path. Even though the practical impact appears to be local DoS and triggering is privileged/timing-dependent, UAF cases should not be auto-closed without manual validation of reclaim and privilege-boundary scenarios. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net: pktgen: fix proc entry use-after-free Commit: 4ef801b838d85c0ea5852c50667f7344ce3b6cd0 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4ef801b838d85c0ea5852c50667f7344ce3b6cd0 Commit description: pktgen_change_name() replaces pkt_dev->entry while holding t->if_lock. pktgen_remove_device() removes the same entry before _rem_dev_from_if_list() takes that lock. This allows the following interleaving: CPU 0 (NETDEV_CHANGENAME) CPU 1 (kpktgend) if_lock(t) proc_remove(pkt_dev->entry) proc_remove(pkt_dev->entry) pkt_dev->entry = proc_create_data(...) if_unlock(t) The kthread can pass the stale proc_dir_entry to proc_remove() after the rename path has freed it. A reproducer with a widened race window reports: BUG: KASAN: slab-use-after-free in proc_remove+0x78/0x80 Read of size 8 at addr ffff8881478fea70 by task kpktgend_0/67 Call Trace: proc_remove+0x78/0x80 pktgen_remove_device.isra.0+0x11c/0x4c0 pktgen_thread_worker+0x1214/0x6bc0 kthread+0x2c6/0x3b0 Allocated by task 95: __proc_create+0x204/0x790 proc_create_data+0x72/0xe0 pktgen_thread_write+0xd61/0x1510 Freed by task 28: kmem_cache_free+0xcb/0x3d0 proc_free_inode+0x5b/0x80 rcu_core+0x50a/0x1850 The buggy address belongs to the object at ffff8881478fea00 which belongs to the cache proc_dir_entry of size 192 Move proc_remove() into the if_lock-protected list removal helper. Keep it before list_del_rcu() to preserve the ordering required by add_device(). The rename path must then finish replacing the entry before removal, or it observes that the device is no longer on the list. Fixes: 39df232 ("[PKTGEN]: fix device name handling") Cc: stable@vger.kernel.org Signed-off-by: Chengfeng Ye Reviewed-by: Simon Horman Link: https://patch.msgid.link/20260719145740.2888967-1-nicoyip.dev@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/core/pktgen.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=4ef801b838d85c0ea5852c50667f7344ce3b6cd0 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74479 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74479 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:H/UI:N/S:U/C:N/I:N/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: 2 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: 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).