From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98856][MODERATE 7.0] kprobes: Skip disarmed probes when checking optkprobe overlap Date: Sat, 24 Oct 2026 09:09:20 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98856 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: 5 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 985a568171e7bdba6dcde3420d0e5bb515813457 List-Id: CVE: CVE-2026-98856 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: kprobes: Skip disarmed probes when checking optkprobe overlap Commit: 985a568171e7bdba6dcde3420d0e5bb515813457 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=985a568171e7bdba6dcde3420d0e5bb515813457 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98856 Analysis date: Sat, 24 Oct 2026 09:09:20 -0400 ActionableScore: 5 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: An attacker able to manage the required kprobes can overwrite one byte of an active optimized jump displacement, causing corrupted kernel control flow and a credible host crash. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98856 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98856 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-2026-98856 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98856 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE_KPANIC RESULT=SAME (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:H/I:H/A:H';*CWE-20;CWE-691;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:H';BEST CVSS score: '7';DESCR 'An x86 optkprobe replaces five bytes of kernel text with a jump. An inactive probe inside that range could stop overlap lookup before the active optimized probe was found, allowing a new INT3 to overwrite the final byte of the active jump displacement and redirect kernel execution to an incorrect address. The demonstrated primitive is kernel text and control flow corruption with a credible kernel crash, while reliable arbitrary code execution or information disclosure is not established. For the CVSS the PR:H base value reflects that direct kprobe registration normally requires privileged tracing access. For the CVSS the PR:L paranoid value covers deployments that delegate tracing capabilities or expose probe management to a less privileged service account. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the ActionableScore threshold 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_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4. The independent weaker Aegis shadow evaluated CVSS 2.0 and ActionableScore 1 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE SIMPLEFIX LINUS KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 PrimitiveClass=CLASS_A RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 5. * Conservative score: 5; no floor or cap applied. * Raw paranoid score: 5. * Paranoid score: 5; delegated tracing is credible but not sufficiently proven for another reachability point. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 strong corruption primitive: attacker-arranged probes cause an INT3 byte to overwrite the displacement of an active five-byte kernel-text jump. * +2 strong exploit leverage: the corrupted displacement is subsequently consumed by CPU execution and redirects kernel control flow to an incorrect address. This is more than passive metadata corruption, although the destination is not shown to be arbitrarily controlled. * +1 reliable kernel crash/strong DoS: executing the malformed jump credibly causes an invalid control transfer and kernel fault. * No extra Availability point: it would duplicate the same crash. * No C/I points: arbitrary code execution, disclosure, credential modification, and a controlled destination are not established. * No local-unprivileged point or privilege penalty: the complete registration, disabling, optimization, and arming interface permissions are unresolved. * NEW52/B5-R does not apply: this is neither a retry-accumulated heap OOB write nor heap corruption. * B4-PENDING does not apply: no authorization DENY-to-ALLOW defect exists. 3. Reachability analysis The trigger requires control over placement and state transitions for probes A, B, and C, including a disarmed probe inside an active optimized jump. Direct kprobe management normally requires privileged tracing access, but the supplied evidence does not establish whether the complete sequence requires host-administrator-equivalent power or works through a delegated tracing service/capability. No namespace-scoped complete path, ordinary-user access, special hardware, or timing race is shown. The sequence is state-dependent but not demonstrated to require a narrow race. 4. Primitive and severity reading The exact primitive is a constrained one-byte kernel-text overwrite: `0xcc` replaces the final displacement byte of a live optimized jump. The active privileged consumer is CPU instruction execution, which uses the corrupted displacement for control flow. A credible delegated tracing boundary remains unresolved, so the active-state trust-boundary rule preserves mandatory review. This is CLASS_A because executable kernel state and subsequent control flow are directly corrupted. It is not a UAF, and neither arbitrary write nor reliable code execution is proven. ImportantCandidate is YES and auto-downgrade is disallowed because the corrupted active jump is actually executed, leaving material non-crash leverage unresolved. 5. One-sentence report phrase An attacker able to manage the required kprobes can overwrite one byte of an active optimized jump displacement, causing corrupted kernel control flow and a credible host crash. 6. Manual review advice MANUAL CHECK REQUIRED Determine the exact kprobe-management privilege boundary and whether probe-address selection can turn the constrained displacement corruption into a repeatable useful control-flow target. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: kprobes: Skip disarmed probes when checking optkprobe overlap Commit: 985a568171e7bdba6dcde3420d0e5bb515813457 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=985a568171e7bdba6dcde3420d0e5bb515813457 Commit description: On x86, an optkprobe at A replaces five bytes with a jump. If a disabled probe B is at A+2, get_optimized_kprobe() stops at B when arming a new probe C at A+4. It leaves A optimized: A A+1 A+2 A+3 A+4 A's jump | e9 | d0 | d1 | d2 | d3 | after C | e9 | d0 | d1 | d2 | cc | The INT3 for C overwrites the last byte of A's jump displacement, so execution can jump to the wrong address. B can have prepared optinsns while disarmed, but has no jump to unoptimize. Continue past disarmed and unprepared probes to find the active optimized probe before arming a probe in its jump. Link: https://lore.kernel.org/all/20260930053618.104498-1-leon.hwang@linux.dev/ Fixes: afd6625 ("kprobes: Introduce kprobes jump optimization") Cc: stable@vger.kernel.org Signed-off-by: Leon Hwang Signed-off-by: Masami Hiramatsu (Google) Signed-off-by: Greg Kroah-Hartman Changed files: kernel/kprobes.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=985a568171e7bdba6dcde3420d0e5bb515813457 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98856 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98856 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:L/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: unknown Paranoid ActionableScore: 5 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).