Windows Kernel TOCTOU CVE-2024-30099: Patch June 2024 for Local Privilege Escalation

Microsoft confirmed a Windows kernel elevation-of-privilege flaw tracked as CVE-2024-30099 on June 11, 2024 — a time-of-check/time-of-use (TOCTOU) race-condition in kernel code that Microsoft rated as an important local Elevation of Privilege (EoP) and patched in the June 11, 2024 cumulative updates; administrators should treat this as a priority patching item for affected Windows builds.

Background / Overview​

CVE-2024-30099 is cataloged as a Windows Kernel Elevation of Privilege Vulnerability with the underlying weakness classified as CWE‑367: Time‑of‑check Time‑of‑use (TOCTOU) race condition. The National Vulnerability Database (NVD) lists the CVE with a publication date of June 11, 2024 and explicitly identifies the TOCTOU class, a pattern that occurs when kernel code checks a resource state and later uses it without adequate re-verification — opening a narrow timing window attackers can exploit. Independent vulnerability trackers and vendor analysis corroborate Microsoft’s characterization: the vulnerability received a CVSS v3.1 base score of 7.0 (High) with the vector AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H, indicating a local attack vector, low privileges required, and high confidentiality/integrity/availability impact if exploitation succeeds. This score and vector appear in multiple vendor databases that indexed Microsoft’s advisory. Why this matters: kernel-level EoP bugs are classic post‑compromise force multipliers. If an attacker who already has local code execution (for example a malicious user process or a malware foothold) can reliably win the race window, they may be able to convert that foothold into SYSTEM privileges and full control over the host. That is the operational risk defenders must prioritize.

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Technical anatomy — what a TOCTOU race in the Windows kernel looks like​

A TOCTOU race condition arises when code performs a security-relevant check (the time-of-check) and subsequently uses the verified resource (the time-of-use) without a robust lock or validation that preserves invariants across the interval. In kernel code, that can mean:

• file or object metadata is validated and then used while another thread or actor modifies the underlying resource, or
• pointers or handles are validated for ownership or bounds and later dereferenced after the resource was freed or reallocated, allowing attacker-controlled memory to be introduced.

In practical exploitation chains, an attacker typically must coordinate multiple threads, perform allocator grooming, or trigger specific kernel APIs repeatedly until the narrow window for mis-sequenced checks opens. Because the vulnerable code runs in kernel-mode, even a short-lived corruption can be escalated into process token manipulation, arbitrary kernel memory writes, or other powerful primitives that yield SYSTEM-level code execution. The NVD record and independent trackers both map CVE-2024-30099 to CWE‑367 (TOCTOU), supporting this attack model.

Exploit complexity and attacker prerequisites​

• Attack vector: Local — the attacker must be able to execute code on the host under a non‑privileged account or induce a victim process to run crafted inputs.
• Privileges required: Low — an ordinary authenticated user account is sufficient to attempt exploitation.
• Attack complexity: High — reliably winning TOCTOU windows often demands careful timing, multi-threaded triggers, and precise environment control. Multiple vendors that indexed Microsoft’s advisory mark the complexity higher even though the final payoff is significant.

Keep in mind: “High complexity” does not equal “no risk”. Skilled exploit authors and automated fuzzing techniques have repeatedly turned timing-window bugs into reliable exploits once patches or patch diffs appear publicly.

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Affected systems and patch mapping (what to patch)​

Microsoft addressed CVE-2024-30099 in the regular June 11, 2024 cumulative updates. The June cumulative KBs for each servicing branch contain fixes that map to this CVE; for example, the Windows 10/11 and Server cumulative KB articles released on June 11, 2024 list security fixes in that release wave. System administrators must map CVE→KB→SKU precisely in their environment, verify the correct KB for each OS build, and deploy via the organisation’s standard update channels (WSUS, SCCM/ConfigMgr, Intune, or manual deployment). Key operational points:

• Confirm affected host OS build numbers against your inventory and Microsoft’s KB mappings before deploying. Rapid7 and other vendors aggregated the KB identifiers used in the June 2024 rollup that remediate kernel EoPs, providing a convenient cross‑check to Microsoft’s support pages.
• Apply the June 11, 2024 cumulative that corresponds to each SKU (the update will typically replace kernel binaries and require a reboot). Validate the installed OS build after the reboot to ensure the update applied successfully.
• For highly controlled or air‑gapped environments, plan a test→pilot→broad rollout and confirm service and application compatibility in the pilot ring before completing mass updates.

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Exploit likelihood and telemetry — what the public record shows​

Public intelligence and exploitation prediction metrics for CVE-2024-30099 are mixed but lean toward low near-term mass exploitation with a non‑zero probability of targeted abuse:

• The EPSS (Exploit Prediction Scoring System) reported a very low probability for near-term exploitation in some mirrors, while other trackers showed small but non-negligible scores; different aggregation services produce different EPSS/percentile values due to differing models and update cadences. This divergence underscores the importance of using vendor advisories and patching rather than relying solely on probabilistic exploit scores.
• Several security vendors listed CVE-2024-30099 as “Exploitation More Likely” in the June 2024 bulletin roundup for Windows kernel EoPs, making it worthy of accelerated patching within enterprise windows. Tenable’s June Patch Tuesday writeup specifically flagged this CVE among kernel EoPs that month as requiring prioritization.

Important caveat: some public aggregators and mirrors claim the presence of a public proof-of-concept (PoC) on GitHub. that assertion was inconsistent across sources and could not be reliably corroborated by canonical vendor advisories (Microsoft) or by the NVD entry at the time of review — treat any third‑party PoC claims as unverified until you can validate the repository and test it in a safe lab. If you encounter a PoC repository, verify its origin, review the code cautiously offline, and do not test it on production systems.

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Detection, hunting and short‑term mitigations​

When vendor advisories with limited public exploit details are published, defenders must rely on behavioral detection and compensating controls rather than signature matching of exploit code.

Short-term detection signals to prioritize​

• Unexpected process elevation to SYSTEM from non‑privileged processes — correlate Event IDs for process creation and token changes with contextual process ancestry.
• Recurrent crashes or BSODs that reference kernel components after unusual user-space activity; sudden host instability following repeated similar user actions is suspicious.
• High-frequency or anomalous local activity that attempts to stress kernel APIs (multiple concurrent threads, rapid device or file operations) — especially from user profiles not normally exhibiting such loads.

Compensating controls (0–72 hours)​

• Ensure the June 11, 2024 cumulatives are scheduled and prioritized for deployment to pilot and high‑value hosts.
• Restrict local code execution on sensitive hosts: enforce application allow‑listing policies (WDAC/AppLocker) where feasible.
• Reduce the number of accounts with persistent local admin privileges and block unnecessary interactive logons on servers and jump boxes.
• Harden segmentation: isolate developer build servers, imaging or file‑processing hosts, and management jump boxes from general user workstations.
• Tune EDR/AV to alert on abnormal DeviceIoControl/IOCTL patterns, suspicious token duplications, or low‑privileged processes spawning SYSTEM children.

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Patching playbook — practical steps for administrators​

• Inventory: Use your asset management tool to create an authoritative list of Windows builds and SKUs in your environment. Map each host to Microsoft's KB for the June 11, 2024 cumulative (use Microsoft’s support pages and the Security Update Guide to verify KB numbers for each build).
• Test: Apply the update to a small pilot group that represents a cross-section of production roles (domain controllers, admin workstations, Hyper‑V hosts, VDI infrastructure). Validate critical functions (authentication, backups, virtualization tasks).
• Deploy: Stage broad rollout in prioritized waves — start with internet‑facing management hosts, domain controllers and jump boxes, then expand to remaining endpoints. Schedule reboots according to maintenance windows.
• Verify: Post‑deployment, confirm the OS build numbers and driver versions reported by the KB article. Use Windows Update history, systeminfo, or inventory scanners to assert success.

If you cannot patch immediately, apply the compensating controls listed above and raise the alerting sensitivity for local privilege escalations in your SIEM/EDR platforms.

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Confidence in the public details — how authoritative is the record?​

Microsoft’s Security Update Guide (MSRC) is the canonical vendor record: an entry there signals vendor acknowledgement and that remediation packages exist for supported SKUs. Security operations teams should use the MSRC mapping and Microsoft KB pages as the authoritative source for KB→SKU mappings rather than third‑party CVE mirrors. Independent security vendors and trackers provide useful operational context and prioritization guidance, but the vendor KB is the deterministic deployment unit. The “confidence” metric that Microsoft and other vendors sometimes surface reflects how certain the public record is about both the vulnerability’s existence and the technical detail available. A vendor‑acknowledged and patched CVE has high confidence in existence even when low‑level exploit mechanics are intentionally omitted from advisories — that omission is common for kernel bugs to limit short‑term weaponization. File-level community briefings and vendor summaries explain how to interpret those confidence signals for patch triage.

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Risk analysis — strengths of the response, residual risk, and recommended priorities​

Notable strengths in the vendor response and the public record

• Microsoft issued a patch in the June 11, 2024 cumulative updates and listed the CVE in its Security Update Guide, which is the authoritative remediation mapping for operators. Deploying those updates is the most effective mitigation.
• Multiple independent trackers and reputable security vendors indexed CVE-2024-30099 and published concise operational guidance and CVSS/CWE attributions, which improves enterprise situational awareness and prioritization.

Residual risks and reasons for caution

• The public advisories intentionally omit low-level exploit mechanics; until independent technical analyses or patch diffs are available, defenders cannot know the precise exploitation primitives or whether there are multiple distinct exploit paths. Treat vendor descriptions as authoritative for remediation, but do not assume completeness of the public technical narrative.
• Claims of a public PoC appear in some mirrors but are inconsistent. Do not assume a safe posture based on the absence of a widely confirmed public PoC — private or targeted exploitation remains possible. If a PoC is announced, treat it as an escalation in urgency and accelerate patching and detection hunts.

Operational priorities (ranked)

• Patch affected hosts with the June 11, 2024 cumulative updates and reboot to complete installation. Validate via build numbers.
• Prioritize domain controllers, management jump boxes, virtualization hosts, and admin workstations in your deployment timetable.
• If patching is delayed, enforce application allow‑listing, restrict interactive logons, and increase EDR sensitivity for local escalation patterns.
• Conduct targeted hunts for anomalous SYSTEM escalations and kernel-related crashes in the timeframe around your patching windows. Preserve forensic artifacts (memory images and WER dumps) if you suspect exploitation.

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Quick checklist for Windows administrators​

• Confirm which Windows builds in your estate are older than the fixed builds referenced in Microsoft’s June 11, 2024KBs.
• Schedule and test the June 11, 2024 cumulative updates in a pilot ring.
• Harden local privilege and application execution policies while updates are staged.
• Tune EDR to alert on suspicious DeviceIoControl/IOCTL, token duplication, and process ancestry indicating SYSTEM elevation.
• Preserve forensic data if you suspect exploitation — memory captures and minidumps are essential.

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Closing analysis and takeaway​

CVE-2024-30099 is a confirmed Windows kernel TOCTOU race-condition that Microsoft patched in the June 11, 2024 cumulative update cycle. The technical class (CWE‑367), the CVSS 3.1 severity (7.0), and the vendor remediation are corroborated across multiple authoritative sources and industry trackers; administrators should treat this as an operational priority — verify KB mappings, test updates in a pilot ring, and then deploy broadly. The public record does not fully disclose low‑level exploit mechanics — intentionally — and claims about public PoCs are inconsistent across mirrors. That means defenders must rely on prompt patching, compensating controls, and behavioral detection rather than waiting for community exploit details. The most reliable protection is the vendor-supplied update; once deployed and validated, the residual risk drops substantially. Administrators who prioritize the CVE→KB→build mapping, harden local privilege controls, and tune detection for kernel‑level escalation indicators will substantially reduce organizational exposure to this class of Windows kernel elevation‑of‑privilege vulnerabilities.

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Source: MSRC Security Update Guide - Microsoft Security Response Center