From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74619][MODERATE REGULAR] ovl: don't warn when the mount is completed from another user namespace Date: Sat, 22 Aug 2026 16:39:46 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74619 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: 3 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: 513478092966dc9818d96dd2b3ed613fd2f6e30e List-Id: CVE: CVE-2026-74619 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: ovl: don't warn when the mount is completed from another user namespace Commit: 513478092966dc9818d96dd2b3ed613fd2f6e30e Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=513478092966dc9818d96dd2b3ed613fd2f6e30e Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74619 Analysis date: Sat, 22 Aug 2026 16:39:46 -0400 ActionableScore: 3 ActionableScore lower bound: 2 Actionable bucket: Ordinary Moderate / Low-like. Not an Important candidate Manual review required: NO Summary: A local unprivileged user can repeatedly trigger a reachable overlayfs WARN_ON by completing an fscontext from another user namespace, causing log flooding and possible kernel panic on panic_on_warn systems, but no memory corruption or privilege escalation primitive is shown. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74619 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74619 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74619 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-617;CWE-755;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'overlayfs ovl_fill_super used a reachable WARN_ON when an fscontext fd created in one user namespace was completed from another user namespace. A local unprivileged user can reach this path by creating user and mount namespaces, opening an overlay fscontext, passing the fd, and issuing FSCONFIG_CMD_CREATE from a different namespace context. For the CVSS the PR:L is used because local code execution as an unprivileged user is required, but no administrative capability is required in the described namespace setup. The issue is not network reachable and does not provide a memory corruption primitive. Impact is denial of service through repeated WARN log flooding and kernel tainting, with full kernel panic possible on systems configured with panic_on_warn.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like. Not an Important candidate (with actual score 3) YES DISK WARNONLY HARDWARE LINUS INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 3 * Final recommended bucket: **Ordinary Moderate / Low-like. Not an Important candidate**:: ## 2. Signal breakdown * Local unprivileged trigger: +1 The commit explicitly describes a trigger using plain unshare, fsopen, fd passing, and fsconfig without administrative capability. * Reliable WARN/log DoS concern: +1 The WARN_ON is reachable repeatedly and can flood logs and taint the kernel. * Paranoid panic_on_warn availability impact: +1 On systems booted with panic_on_warn, the reachable WARN_ON can become a full kernel panic. This is configuration dependent, so it is counted only in the paranoid score. No memory corruption signal is applied. The patch only removes a reachable WARN_ON and keeps refusing the mount. There is no UAF, OOB access, double free, type confusion, arbitrary write, refcount takeover, or stale callback primitive. ## 3. Reachability analysis A local unprivileged user can trigger the warning when unprivileged user namespaces are available. The path uses fsopen for overlayfs in one user namespace and completes the fscontext from another namespace via fsconfig. This is not network reachable. Containers or namespace-enabled environments may make the trigger more practical, but the issue still requires local code execution. The affected overlayfs and fscontext paths are common enough to matter, but the severe panic outcome depends on panic_on_warn being enabled. ## 4. Severity interpretation This behaves like an ordinary Moderate or Low-like local denial of service issue rather than an Important-class vulnerability. The realistic impact is repeated kernel warnings, log flooding, kernel tainting, and possible panic only on panic_on_warn systems. Theoretical escalation is not supported by the patch because execution stops at the same error path and no memory lifetime or corruption primitive is introduced. ## 5. One-sentence report phrase A local unprivileged user can repeatedly trigger a reachable overlayfs WARN_ON by completing an fscontext from another user namespace, causing log flooding and possible kernel panic on panic_on_warn systems, but no memory corruption or privilege escalation primitive is shown. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED This can be auto-closed for Important triage purposes because it is a local WARN/log flooding DoS with configuration-dependent panic behavior and no evidence of memory corruption, information disclosure, integrity impact, or privilege escalation. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ovl: don't warn when the mount is completed from another user namespace Commit: 513478092966dc9818d96dd2b3ed613fd2f6e30e Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=513478092966dc9818d96dd2b3ed613fd2f6e30e Commit description: fsopen() records the caller's user namespace in fc->user_ns and hands back an ordinary file descriptor. Nothing ties the task that calls fsconfig(FSCONFIG_CMD_CREATE) to the task that created the context. The fd is inherited across fork() and exec() and it can be passed over a unix socket. Completing a context from another user namespace is allowed on purpose. vfs_cmd_create() authorizes the create with mount_capable(), which for FS_USERNS_MOUNT checks ns_capable(fc->user_ns, CAP_SYS_ADMIN), and that succeeds for a task holding CAP_SYS_ADMIN in an ancestor of fc->user_ns. So an unprivileged task can reach the WARN_ON() in ovl_fill_super(): create a user and a mount namespace in a child, call fsopen("overlay") there, send the fscontext fd to the parent and let the parent issue FSCONFIG_CMD_CREATE. Both namespaces come from a plain unshare(1) and no capability is needed anywhere: WARNING: fs/overlayfs/super.c:1551 at ovl_fill_super+0x7b9/0x1e20 [overlay] CPU: 3 UID: 1000 PID: 3243376 Comm: fswarn Call Trace: get_tree_nodev+0x71/0xa0 ovl_get_tree+0x15/0x20 [overlay] vfs_get_tree+0x2a/0x100 vfs_cmd_create+0x60/0xf0 __do_sys_fsconfig+0x4b2/0x500 The child needs the mount namespace because fsopen() itself gates on may_mount(), which asks for CAP_SYS_ADMIN in the user namespace owning the caller's mount namespace. fsconfig() doesn't repeat that check. It is a WARN_ON() and not a WARN_ON_ONCE(), so the condition can be raised in a loop to taint the kernel and flood the log, and it panics a kernel booted with panic_on_warn. Keep refusing the mount and stop warning about it. ovl_parse_param() already spells a user namespace check this way for Opt_override_creds. Fixes: 1784fbc ("ovl: port to new mount api") Cc: stable@vger.kernel.org # v6.5+ Link: https://patch.msgid.link/20260802-work-fill_super-warn-v1-1-4e987911a39a@kernel.org Reviewed-by: Jan Kara Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman Changed files: fs/overlayfs/super.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=513478092966dc9818d96dd2b3ed613fd2f6e30e ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74619 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74619 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:L/PR:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: 2 Paranoid ActionableScore: 3 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).