From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98983][MODERATE 7.0] unshare: don't drop active namespace references that were never taken Date: Mon, 26 Oct 2026 14:21:10 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98983 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: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 56fe03a0c05dba4c5f6a23c391f96de1614a098c List-Id: CVE: CVE-2026-98983 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: unshare: don't drop active namespace references that were never taken Commit: 56fe03a0c05dba4c5f6a23c391f96de1614a098c Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56fe03a0c05dba4c5f6a23c391f96de1614a098c Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98983 Analysis date: Mon, 26 Oct 2026 14:21:10 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate Manual review required: YES Summary: A low-privilege local failure path can corrupt active namespace reference accounting and hide still-live namespaces from administrative enumeration. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98983 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98983 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-2026-98983 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98983 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';CWE-911;CWE-682;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '3.6';DESCR 'A logic and reference accounting error in the ksys_unshare failure path calls put_nsproxy on an nsproxy that was prepared but never installed into a task. This drops active namespace references that were never acquired, can underflow the active count for new namespaces, and can remove namespaces still used by the caller from listns visibility. For the CVSS the PR:L value is selected because triggering requires a local process to execute unshare in a context where its real UID differs from its effective UID. AC:H is selected because set_cred_ucounts must also fail through an alloc_ucounts allocation failure. The demonstrated impact is incorrect namespace accounting and administrative visibility rather than UAF, arbitrary memory access, or privilege escalation. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 3.6 and the production ActionableScore returned 4 with recommendation Actionable Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage LOW to MODERATE_KPANIC because the ActionableScore threshold rule was applied. KP and FD specialist checks stage MODERATE_KPANIC to MODERATE because KP specialist did not establish a qualifying panic. final reconciliation stage MODERATE to MODERATE_KPANIC because the cross model evidence reconciliation rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN3 and DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.1 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 4) MAYBE INIT WARNONLY LEAK LINUS INCREASED_FROM_LOW_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN3 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 PrimitiveClass=CLASS_B RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 3. * Conservative score: 3; no floor or cap applied. * Raw paranoid score: 4. * Paranoid score: 4; no floor or cap applied. * Final recommended bucket: **Actionable Moderate**:: 2. Signal breakdown * +2 — Concrete active-state corruption: `put_nsproxy()` invokes active-reference teardown on an nsproxy never installed in a task. New namespace active counts underflow, while namespaces still used by the caller lose active references. * +1 — Below-host-admin local trigger: supplied evidence describes a local PR:L process invoking `unshare()` with differing real/effective UIDs. * +1 — Proven downstream integrity effect: the corrupted namespace state is later consumed by namespace enumeration, causing live namespaces to disappear from `listns()`. * -1 — Hard trigger condition: `set_cred_ucounts()` must encounter an `alloc_ucounts()` allocation failure. * Paranoid +1 — Specific unresolved trust-boundary consequence: attacker-induced active namespace bookkeeping is consumed by administrative namespace-discovery machinery; effects beyond loss of visibility are not established. No UAF, heap overwrite, arbitrary write, authorization bypass, crash, disclosure, or privilege escalation is shown. No extra availability or confidentiality point is awarded. 3. Reachability analysis The trigger is local and requires `unshare()`, differing real/effective UIDs, and allocation failure. The supplied PR:L assessment supports below-host-admin reachability, but does not establish that every required namespace operation is available through attacker-created user namespaces; therefore namespace-scoped privilege remains unknown. Numeric host UID 0 is not shown as required. The allocation-failure prerequisite supports high complexity, but does not negate the concrete state corruption. 4. Primitive and severity reading The primitive is incorrect decrement of active namespace references, including underflow and removal of still-live namespaces from enumeration. This is active structured-state/reference corruption, not a real UAF or ordinary memory overwrite. The later consumer and namespace/administrative trust boundary are specific, but broader security consequences remain unknown. Under the active-state trust-boundary rule, this warrants an Important candidate and mandatory review without asserting Important severity, panic, or privilege escalation. Auto-downgrade is disallowed because the non-panic integrity chain remains unresolved. 5. One-sentence report phrase A low-privilege local failure path can corrupt active namespace reference accounting and hide still-live namespaces from administrative enumeration. 6. Manual review advice MANUAL CHECK REQUIRED Review whether corrupted active counts affect namespace lifetime, host-level enumeration, cleanup, or policy consumers beyond the demonstrated `listns()` visibility loss. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: unshare: don't drop active namespace references that were never taken Commit: 56fe03a0c05dba4c5f6a23c391f96de1614a098c Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56fe03a0c05dba4c5f6a23c391f96de1614a098c Commit description: Active references on the namespaces of an nsproxy are taken when the nsproxy is installed into a task in switch_task_namespaces() and copy_namespaces() and dropped again by put_nsproxy() through deactivate_nsproxy(). But ksys_unshare() calls put_nsproxy() on an nsproxy that was never installed when set_cred_ucounts() fails. The new namespaces of that nsproxy go from zero to minus one and the namespaces shared with the caller lose a reference that belongs to the nsproxy the caller keeps using: WARNING: kernel/nscommon.c:171 at __ns_ref_active_put+0x1cd/0x230 nsproxy_ns_active_put deactivate_nsproxy ksys_unshare Afterwards the namespaces the caller lives in aren't listed by listns() anymore. set_cred_ucounts() only fails when alloc_ucounts() can't allocate and it only allocates when the real uid of the caller differs from its effective uid. Commit cefd55b ("nsproxy: fix free_nsproxy() and simplify create_new_namespaces()") separated the two cases on purpose. nsproxy_free() frees an nsproxy that was prepared but never installed and that's what a failed setns() uses in put_nsset(). Export it and use it for a failed unshare() as well. Fixes: a98621a ("unshare: fix nsproxy leak in ksys_unshare() on set_cred_ucounts() failure") Cc: stable@vger.kernel.org # v7.1+ Link: https://patch.msgid.link/20260930-work-mount-fixes-3-v1-16-be34c83956ae@kernel.org Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman Changed files: kernel/nscommon.c include/linux/nsproxy.h kernel/fork.c kernel/nsproxy.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=56fe03a0c05dba4c5f6a23c391f96de1614a098c ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98983 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98983 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:N/I:L/A:N The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L The Best / paranoid CVSS score: 3.6 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: 3 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: 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).