From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-63831][IMPORTANT] mac802154: llsec: add skb_cow_data() before in-place crypto Date: Sun, 19 Jul 2026 10:19:20 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-63831 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 8 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 3a2b378b3a9ca75d3518d879148d2ad25b5714a9 List-Id: CVE: CVE-2026-63831 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: mac802154: llsec: add skb_cow_data() before in-place crypto Commit: 3a2b378b3a9ca75d3518d879148d2ad25b5714a9 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3a2b378b3a9ca75d3518d879148d2ad25b5714a9 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63831 Analysis date: Sun, 19 Jul 2026 10:19:20 -0400 ActionableScore: 8 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: mac802154 LLSEC performs in-place crypto on skb data that may be shared with other clones, allowing adjacent 802.15.4 traffic to cause shared skb corruption and possible use-after-free leading to kernel crash or worse memory-corruption impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63831 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63831 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-2026-63831 IMPORTANT CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;*CWE-787;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'mac802154 LLSEC can perform in-place crypto on skb data that is still shared with other skb clones. On the RX path a received 802.15.4 frame may be cloned before it is passed to multiple subscribers, and later LLSEC decrypt may modify the shared buffer through the crypto scatterlist. This can silently corrupt data visible to other clones and in the worst case can become a use-after-free when another clone releases the shared backing storage while crypto still writes through it. For the CVSS the PR:N is used for the paranoid score because an attacker does not need a local account if they can inject or influence reachable 802.15.4 traffic in the adjacent WPAN environment. The issue is adjacent-network reachable rather than Internet remote. Impact is at least denial of service via kernel crash and data corruption, with a defensible worst case of confidentiality and integrity impact because the bug class includes shared skb memory corruption and UAF reports.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES DANGER UAF SKB KERNEL_PANIC_PLUS_UAF IPV6 KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Triggered signals: * Remote reachable / network-triggerable: +2 The vulnerable path is reachable through IEEE 802.15.4 traffic when mac802154 LLSEC is enabled. This is adjacent-network reachable, not Internet remote. * Generic memory corruption, strong corruption primitive: +2 The commit explicitly describes shared skb data corruption and slab-use-after-free reports. * Real lifetime corruption: +1 The bug can involve writes through skb data that may already have been freed by another clone. * Reliable kernel crash / strong DoS: +1 KASAN/KMSAN slab-use-after-free and kernel crashes are explicitly mentioned. * Weak LPE concern: +1, paranoid only UAF with kernel writes into freed/shared skb backing storage is a plausible escalation concern, but no controlled reclaim or exploit primitive is demonstrated. * Dirty-Pipe-like shared ownership/COW concern: +1, paranoid only The root issue is missing copy-on-write isolation before in-place writes to data shared by skb clones. This is not page-cache corruption, so it should not receive the full Dirty-Pipe-like +2 treatment. * Confidentiality impact plausible: +1, paranoid only Possible only as a consequence of kernel memory corruption. Not demonstrated. * Integrity impact plausible: +1 Silent corruption of data visible to other skb clones is directly described. Subtracted signals: * Hard or unreliable race / special timing required: -1 The strongest UAF scenario depends on concurrent clone lifetime and freeing behavior. * Rare AND difficult-to-reach subsystem/configuration: -1 Requires IEEE 802.15.4 with LLSEC/security enabled, which is not a broad default networking path. ## 3. Reachability analysis An attacker does not need a local account if they can inject or influence reachable IEEE 802.15.4 traffic in the adjacent WPAN environment. This supports PR:N in a CVSS-style paranoid interpretation, but the exposure is adjacent-network rather than general Internet remote. The vulnerable path depends on mac802154 LLSEC being configured and active. This is not a common default server exposure, but it is realistic for systems using 802.15.4 security. Namespaces are not the main factor here because the primary trigger can be external radio traffic rather than a local userspace API. Call-site confidence: high. The patch shows the exact encrypt and decrypt call sites and places skb_cow_data() immediately before in-place crypto. ## 4. Severity interpretation This is not an ordinary Moderate cleanup. The patch addresses an skb ownership and lifetime violation where in-place crypto can modify shared data and can lead to use-after-free. Realistic impact includes adjacent-network DoS and data corruption under specific LLSEC traffic conditions. The conservative score treats this as Actionable Moderate because the subsystem is niche and the strongest UAF condition has timing/configuration requirements. The paranoid score reaches Strong Important candidate because the patch context explicitly identifies kernel UAF and shared skb memory corruption, which should not be auto-closed without manual review. ## 5. One-sentence report phrase mac802154 LLSEC performs in-place crypto on skb data that may be shared with other clones, allowing adjacent 802.15.4 traffic to cause shared skb corruption and possible use-after-free leading to kernel crash or worse memory-corruption impact. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch explicitly fixes shared skb memory corruption and reported slab-use-after-free, and the trigger can be adjacent-network reachable in affected 802.15.4 LLSEC deployments. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: mac802154: llsec: add skb_cow_data() before in-place crypto Commit: 3a2b378b3a9ca75d3518d879148d2ad25b5714a9 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3a2b378b3a9ca75d3518d879148d2ad25b5714a9 Commit description: llsec_do_encrypt_unauth(), llsec_do_encrypt_auth(), llsec_do_decrypt_unauth(), and llsec_do_decrypt_auth() all perform in-place cryptographic transformations on skb data. They build a scatterlist with sg_init_one() pointing into the skb's linear data area and then pass the same scatterlist as both src and dst to the crypto API (e.g. crypto_skcipher_encrypt/decrypt, crypto_aead_encrypt/decrypt). On the RX path, __ieee802154_rx_handle_packet() clones the received skb before handing it to each subscriber via ieee802154_subif_frame(). The cloned skb shares the same underlying data buffer via reference counting. When llsec_do_decrypt() subsequently modifies this shared buffer in place, it corrupts data that other clones -- potentially belonging to other sockets or subsystems -- still reference. On the TX path, similar data sharing can occur when an skb's head has been cloned (skb_cloned() returns true). The fix is to call skb_cow_data() before performing any in-place crypto operation. skb_cow_data() ensures that the skb's data area is not shared: if the skb head is cloned or the data spans multiple fragments, it copies the data into a private buffer that can be safely modified in place. This is the same pattern used by: - ESP (net/ipv4/esp4.c, net/ipv6/esp6.c) - MACsec (drivers/net/macsec.c) - WireGuard (drivers/net/wireguard/receive.c) - TIPC (net/tipc/crypto.c) Without this guard, in-place crypto on shared skb data leads to: - Silent data corruption of other skb clones - Use-after-free when the crypto API scatterwalk writes through a page that has already been freed by another clone's kfree_skb() - Kernel crashes under concurrent 802.15.4 traffic with security enabled (KASAN/KMSAN reports slab-use-after-free) Found by 0sec ( https://0sec.ai ) using automated source analysis. Fixes: 4c14a2f ("mac802154: add llsec decryption method") Fixes: 03556e4 ("mac802154: add llsec encryption method") Cc: stable@vger.kernel.org Reported-by: Doruk Tan Ozturk Closes: https://lore.kernel.org/linux-wpan/20260525161806.96158-1-doruk@0sec.ai/ Reviewed-by: Alexander Lobakin Signed-off-by: Doruk Tan Ozturk Closes: Link: https://lore.kernel.org/20260526183726.56100-1-doruk@0sec.ai Signed-off-by: Stefan Schmidt Signed-off-by: Greg Kroah-Hartman Changed files: net/ipv4/esp4.c net/ipv6/esp6.c drivers/net/macsec.c drivers/net/wireguard/receive.c net/tipc/crypto.c net/mac802154/llsec.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=3a2b378b3a9ca75d3518d879148d2ad25b5714a9 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63831 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63831 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:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7.5 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: 8 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: YES 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).