From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-63829][IMPORTANT] net: ip_gre: require CAP_NET_ADMIN in the device netns for changelink Date: Sun, 19 Jul 2026 10:13:53 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-63829 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: 7 X-AL-KERNEL-ActionableScore-Lower: 6 X-AL-KERNEL-Commit: 9831bc9ecb402957810c2045c663fbfe9b09e296 List-Id: CVE: CVE-2026-63829 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: net: ip_gre: require CAP_NET_ADMIN in the device netns for changelink Commit: 9831bc9ecb402957810c2045c663fbfe9b09e296 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9831bc9ecb402957810c2045c663fbfe9b09e296 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63829 Analysis date: Sun, 19 Jul 2026 10:13:53 -0400 ActionableScore: 7 ActionableScore lower bound: 6 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: GRE and ERSPAN changelink authorization checked CAP_NET_ADMIN only in dev_net(dev), allowing a caller with delegated network admin rights in one namespace to rewrite tunnel parameters owned by another namespace. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63829 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63829 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-2026-63829 IMPORTANT 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:C/C:H/I:H/A:H';CWE-862;CWE-863;CWE-269;CWE-284;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:C/C:L/I:H/A:L';BEST CVSS score: '7.8';DESCR 'GRE and ERSPAN tunnel changelink authorization was incomplete because the rtnetlink path checked CAP_NET_ADMIN only in dev_net(dev), while the tunnel link namespace t net could be different. A caller with network administration rights in the device namespace but not in the tunnel link namespace could still rewrite tunnel parameters that belong to the other namespace. For the CVSS the PR:L is used because the attacker needs local code execution with limited CAP_NET_ADMIN style control in one network namespace, not full host administrative privileges. The issue is not directly network reachable and is triggered through local rtnetlink control plane operations rather than packet traffic. Impact is a cross namespace authorization bypass that can affect tunnel routing and encapsulation policy, with plausible confidentiality impact from traffic redirection, high integrity impact from unauthorized configuration changes, and availability impact from breaking tunnel connectivity.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES REMOTE HARDWARE KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=6 ## 1. ActionableScore * Conservative score: 6 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown * Security-boundary bypass with practical sensitive-object access: +2 The bug bypasses the intended CAP_NET_ADMIN check in the tunnel link netns and allows a caller privileged only in dev_net(dev) to modify a GRE or ERSPAN tunnel owned by another netns. * Cross-boundary isolation/policy bypass: +1 The affected condition is explicitly cross-netns: dev_net(dev) and t->net can differ after device creation or movement. * Confidentiality impact plausible: +1 Unauthorized tunnel reconfiguration can plausibly redirect, mirror, or alter encapsulated traffic paths, especially for ERSPAN/GRE deployments. * Integrity impact plausible: +1 The attacker can rewrite live tunnel parameters without authorization in the tunnel namespace. * Availability impact realistic: +1 Bad tunnel parameters can break tunnel connectivity or disrupt encapsulation policy. * Practical exploit chain strongly implied: +1 for paranoid score only The commit directly describes the missing check and notes that parsers update live tunnel fields before the normal changelink path completes. * Requires CAP_NET_ADMIN in one namespace: 0 penalty No full -2 penalty is applied because the issue bypasses a meaningful namespace/capability boundary. The attacker does not need full host root, only CAP_NET_ADMIN style control in the wrong namespace. * Remote reachable: +0 This is rtnetlink control-plane access, not packet-triggered remote reachability. * Memory corruption / LPE primitive: +0 No UAF, OOB write, type confusion, or arbitrary write is indicated. Call-site confidence: high. The affected changelink entry points and the new authorization check are visible in the patch. ## 3. Reachability analysis The bug is triggered locally through RTM_NEWLINK/changelink operations for ip_gre or erspan devices. The realistic attacker is a process with CAP_NET_ADMIN in dev_net(dev), for example a container or delegated network namespace administrator, but without CAP_NET_ADMIN in the tunnel link namespace t->net. Namespace delegation is central to the impact because the bug exists only when those namespaces differ. The path is not remotely reachable through packet traffic. Exploitation requires GRE or ERSPAN tunnel objects in a cross-netns configuration, so it is configuration-dependent but plausible in containerized or delegated networking environments. ## 4. Severity interpretation This behaves like an Important-candidate access-control and namespace-boundary bypass, not like memory corruption. The realistic impact is unauthorized tunnel reconfiguration with possible traffic redirection, policy bypass, and tunnel disruption. There is no demonstrated kernel memory corruption or direct privilege escalation primitive, so it should not be treated as a memory-safety Important. However, because it breaks a capability boundary across network namespaces and can affect network traffic policy, it should not be auto-closed as an ordinary Moderate. ## 5. One-sentence report phrase GRE and ERSPAN changelink authorization checked CAP_NET_ADMIN only in dev_net(dev), allowing a caller with delegated network admin rights in one namespace to rewrite tunnel parameters owned by another namespace. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This needs manual review because it is a namespace capability-boundary bypass with practical network policy impact, and the real severity depends on whether the affected product allows delegated CAP_NET_ADMIN or container-controlled tunnel device movement. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net: ip_gre: require CAP_NET_ADMIN in the device netns for changelink Commit: 9831bc9ecb402957810c2045c663fbfe9b09e296 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9831bc9ecb402957810c2045c663fbfe9b09e296 Commit description: A tunnel changelink() operates on at most two netns, dev_net(dev) and the tunnel link netns t->net. They differ once the device is created in or moved to a netns other than the one the request runs in. The rtnl changelink path checks CAP_NET_ADMIN only against dev_net(dev), so a caller privileged there but not in t->net can rewrite a tunnel that lives in t->net. Add rtnl_dev_link_net_capable() next to rtnl_get_net_ns_capable() in net/core/rtnetlink.c. It requires CAP_NET_ADMIN in the link netns and is skipped when the link netns is dev_net(dev), where the rtnl path already checked it. The other patches in this series use the same helper. Gate ipgre_changelink() and erspan_changelink() with it, at the top of the op before any attribute is parsed, because the parsers update live tunnel fields first. ipgre_netlink_parms() sets t->collect_md before ip_tunnel_changelink() runs. Commit 8b484ef ("ip6: vti: Use ip6_tnl.net in vti6_siocdevprivate().") added the same check on the ioctl path. This adds it on RTM_NEWLINK. Reported-by: Xiao Liang Closes: https://lore.kernel.org/netdev/CABAhCOSzP1vaThGV35_VnsRCb=87_CPjPVsTHbq905k8A+BuUg@mail.gmail.com/ Fixes: b57708a ("gre: add x-netns support") Cc: stable@vger.kernel.org Signed-off-by: Maoyi Xie Reviewed-by: Kuniyuki Iwashima Link: https://patch.msgid.link/20260612085941.3158249-2-maoyixie.tju@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/core/rtnetlink.c include/net/rtnetlink.h net/ipv4/ip_gre.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=9831bc9ecb402957810c2045c663fbfe9b09e296 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63829 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63829 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:C/C:L/I:H/A:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H The Best / paranoid CVSS score: 7.8 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: 6 Paranoid ActionableScore: 7 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).