CVE-2025-53136: Windows Kernel Info Leak Threat to KASLR (TOCTOU)

A routine security update intended to tighten Windows kernel defenses has instead opened a new attack vector: a reliably exploitable information‑disclosure bug tracked as CVE‑2025‑53136 that leaks kernel addresses on Windows 11 and Windows Server 2022 24H2 builds. The vulnerability—rooted in changes to the kernel function RtlSidHashInitialize() applied while fixing an earlier October 2024 issue—temporarily writes a sensitive kernel pointer into a userland buffer, creating a timing window attackers can win with simple race logic. The result is a powerful primitive for defeating Kernel Address Space Layout Randomization (KASLR) and chaining into full local privilege escalation (LPE) when combined with other kernel weaknesses. (fedisecfeeds.github.io) (rapid7.com)

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Background​

Where the problem came from​

Microsoft issued an October 2024 patch (addressing CVE‑2024‑43511) that altered how SID and token structures are initialized inside the kernel. That code change called RtlSidHashInitialize() with parameters that resulted—under certain execution paths—in the kernel copying a pointer to a TOKEN.UserAndGroups field into a user-provided buffer before overwriting it with a safe value. Although the pointer is removed quickly, the brief exposure is enough for an attacker to read it from user space by racing reads against the write-removal window. Multiple independent analyses and vulnerability databases confirm the link between the October 2024 fix and the new disclosure. (cybersecuritynews.com) (wiz.io)

What systems are affected​

• Windows 11 (24H2) and Windows Server 2022 (24H2) are confirmed vulnerable in the released advisories and community analysis. Public vulnerability trackers and vendor advisories list the CVE and affected SKUs; vendor packages and KB identifiers are being tracked in major vulnerability databases. (nvd.nist.gov) (rapid7.com)

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The technical fault: how the leak actually happens​

The code path and the TOCTOU window​

At the heart of CVE‑2025‑53136 is a time-of-check/time-of-use (TOCTOU) style race triggered by two interacting operations:

• A kernel function (changed as part of the prior CVE fix) momentarily writes a kernel pointer—derived from the process TOKEN structure—into a user-supplied buffer.
• Almost immediately thereafter the code restores a safe value in that buffer.

The transient presence of that pointer in user memory creates a tiny but consistent time window. An attacker who can trigger the vulnerable kernel call and simultaneously sample the userbuffer at the right offset can capture the pointer before it is sanitized. Because the pointer is a kernel-resident address, capturing it reveals layout information that defeats KASLR and gives the attacker a deterministic view into kernel memory layout. Independent analysts who reviewed the patch and the exploit scenario describe that the window is sufficiently wide to make this a reliable primitive rather than an occasional fluke. (cybersecuritynews.com)

The system calls and the race strategy​

Proof-of-concept exploit paths observed in public writeups and technical analyses use two cooperating threads:

• One thread repeatedly calls NtQueryInformationToken() with the TokenAccessInformation information class to force the kernel routine down the vulnerable path.
• A second thread concurrently reads from the user buffer at the offset where the pointer is written, spinning until it captures a non-zero value—the leaked kernel pointer.

Because both threads run in usermode, this can be executed by low‑privilege processes including sandboxed contexts (Low IL or AppContainer), meaning that the attacker model is not limited to administrators or signed code. Crowdfense and other community writeups demonstrate the exploit reliably obtaining kernel pointers in most runs. (fedisecfeeds.github.io) (cybersecuritynews.com)

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Why this matters: consequences for enterprise defenders​

KASLR and kernel hardening undermined​

Modern Windows kernel hardening relies heavily on address randomization and layered mitigations to raise the bar for exploits. By leaking kernel addresses, CVE‑2025‑53136 undermines those protections:

• KASLR becomes ineffective for the leaking process: knowing kernel pointers makes it trivial to compute offsets and target kernel structures or functions.
• Sandbox escapes: sandboxes that prevent exposure to privileged APIs remain vulnerable when a sandboxed app can learn kernel layout and chain to other bugs or driver vulnerabilities.
• Rapid weaponization: once PoCs appear, attackers can weaponize the primitive by combining it with existing write primitives (write-what-where) to modify kernel token fields, flip privilege bits, or perform targeted code execution.

These impacts turn a local information leak—often considered “lower‑severity” than RCE—into a highly actionable foothold that accelerates escalation and post‑compromise movement. (rapid7.com)

Realistic attack chains​

A practical attack leveraging CVE‑2025‑53136 may follow this sequence:

• Low‑privilege code (e.g., malicious app, web sandbox escape, userland malware) runs on the host.
• The malware triggers the NtQueryInformationToken() race to leak a kernel pointer.
• Using that pointer, the attacker crafts or adapts a separate kernel bug (for example, a write-what-where or use‑after‑free in a driver) to overwrite the process TOKEN.Privileges or similar fields.
• The attacker escalates to SYSTEM and achieves persistence, lateral movement, or credential theft.

This “information disclosure → exploit chaining” model is well documented in recent kernel incidents and is precisely the concern raised by researchers. (wiz.io)

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Verification: what the advisories and trackers say​

• The vulnerability was assigned CVE‑2025‑53136 and is listed in public vulnerability trackers with a classification of NT OS Kernel Information Disclosure; NVD and other trackers show the CVE entry and reference the Microsoft Security Update Guide. (nvd.nist.gov)
• Rapid7, Wiz, and multiple security news outlets have published writeups and lists of affected packages and KBs to apply—these independently corroborate the presence and exploitability of the leak. (rapid7.com) (wiz.io)
• Crowd‑sourced and vendor analyses indicate the new leak is tied to changes made while remediating the October 2024 CVE (CVE‑2024‑43511). The researcher(s) reported the issue through a responsible disclosure timeline that began in early April 2025, with Microsoft acknowledging and assigning a CVE later in the cycle. Public writeups summarize that timeline and technical root cause. (cybersecuritynews.com) (fedisecfeeds.github.io)

Note: vendor portals such as the Microsoft Security Update Guide sometimes require interactive access; when MSRC pages are referenced by third‑party indexes, cross‑checking with NVD and reputable vulnerability databases helps verify KB IDs and patch availability. The public dataset entries for CVE‑2025‑53136 indicate Microsoft has published updates; users should confirm the exact KB numbers before declaring systems remediated. (nvd.nist.gov)

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Practical mitigation and immediate actions for IT teams​

Until organizations install Microsoft’s official remediation, adopt the following prioritized steps to reduce exposure and detection windows:

1. Patch aggressively (primary fix)​

• Monitor the Microsoft Security Update Guide for the cumulative update (LCU) and the matching Knowledge Base entries that remediate CVE‑2025‑53136.
• Prioritize Windows 11 (24H2) and Windows Server 2022 (24H2) hosts that accept user logins, host multi-tenant workloads, or run sandboxed applications.
• Validate KB installation across the estate (use WSUS, SCCM/ConfigMgr, or Microsoft Update Catalog fingerprints) before marking systems as remediated. Several vulnerability databases list the KBs tied to the CVE—use these as a checklist but always confirm on Microsoft’s advisory page. (rapid7.com) (wiz.io)

2. Harden local attack surface (compensating controls)​

• Enforce least privilege: remove or tightly control SeDebugPrivilege/SeImpersonatePrivilege from non‑trusted accounts. Limit local admin rights to essential users.
• Restrict execution of untrusted binaries: enable Windows Defender Application Control (WDAC) or AppLocker to prevent unauthorized code from running in user or sandboxed contexts.
• Tighten sandbox policies: reduce the number of allowed capabilities for AppContainer/Low IL apps; restrict access to APIs that could trigger Token queries or device control interfaces.

3. Detection and telemetry tuning​

• Add EDR/SIEM rules to flag abnormal high-frequency calls to NtQueryInformationToken(), unusual repeated reads of user buffers by sandboxed processes, or repeated thread‑spinning behavior around token APIs.
• Watch for post‑exploit signals: suspicious token modifications, unexpected elevation events, or processes with newly granted privileges should raise an immediate alert.
• Ensure kernel-level events and driver load events are being collected by EDR. Maintain memory‑forensics readiness: if compromise is suspected, capture a full memory image and preserve EDR artifacts immediately.

4. Network and host isolation​

• Segment high‑value systems (domain controllers, virtualization hosts, management servers) behind stricter network controls and privileged access workstations (PAWs).
• If you must delay patching for compatibility reasons, isolate affected hosts from user workstations and reduce local login footprints to limit the chance an attacker can chain the local leak into a domain compromise.

5. Regression testing and patch management​

• Add this scenario to your update regression test plans: verify that vendor patches do not introduce TOCTOU/temporary-write regressions in user-copy operations by instrumenting token APIs and testing concurrent access patterns.
• When Microsoft publishes KBs, test the package on representative systems before broad deployment, but prioritize high-risk systems for immediate rollout.

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Detection playbook: signals to hunt​

• Processes creating many handles to LSA, token‑related DeviceIoControl, or repeated calls to TokenAccessInformation.
• Low‑privilege processes performing tight read loops against their own memory pages at offsets consistent with SID/token layouts.
• Sudden token privilege escalations or token structural anomalies appearing in EDR telemetry.
• Unexpected driver loads around virtualization or file system drivers, which are commonly chained with token attacks.

Tune detection rules to reduce false positives but keep low‑latency alerts when combinations of these indicators appear. EDR vendors are updating detections and customers should ingest vendor telemetry signatures as they are released. (wiz.io)

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Readiness checklist for Windows administrators​

• Inventory endpoints and servers running Windows 11 (24H2) and Windows Server 2022 (24H2).
• Confirm patch status against Microsoft’s KBs that remediate CVE‑2025‑53136 (verify on Security Update Guide/NVD/rapid7 listings). (nvd.nist.gov)
• Harden least‑privilege for accounts and services; remove nonessential SeDebugPrivilege.
• Enable WDAC/AppLocker or equivalent controls to block untrusted code execution.
• Tune EDR to detect high‑frequency token queries, rapid userbuffer reads, and sudden token modifications.
• Segment high‑value systems and disable untrusted image mounts where possible.
• Prepare incident response playbooks for memory capture, log preservation, and reimaging procedures.

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Why this incident is a broader lesson in patch engineering​

CVE‑2025‑53136 illustrates an uncomfortable reality: fixes for one vulnerability can inadvertently open different attack surfaces—especially in complex, highly optimized kernel code paths. Processor and compiler optimizations, micro‑optimizations, and small refactors often interact in subtle ways that only surface under specific timing or concurrency scenarios. The kernel must balance performance with defensive semantics; in this case a benign optimization reintroduced a temporary exposure of privileged metadata to user space.
For defenders and vendors alike, the lesson is to treat security fixes with the same threat modeling and concurrent testing applied to feature code: add concurrency tests, fuzz user-to-kernel transitions under stress, and expand code review to consider TOCTOU and micro‑optimization side effects. Several community posts and vulnerability trackers emphasize the need for regression testing specifically targeting user-buffer sanitization in token and SID APIs.

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Technical caveats and what remains unverified​

• Public reporting indicates PoC reliability and the feasibility of capturing the leaked kernel pointer; however, the exact success rate may vary between hardware platforms, CPU microarchitectures, and system load. Researchers report high reliability in lab conditions, but real‑world timing variance can affect results—tune expectations accordingly. (cybersecuritynews.com)
• Some older or out‑of‑support SKUs may not receive the same cumulative updates; verify each product’s KB applicability before assuming coverage. Vendor advisory pages and the Microsoft Update Catalog are the ultimate sources for package IDs. (nvd.nist.gov)
• While no widespread in‑the‑wild exploitation was publicly confirmed at the time of reporting, the primitive is attractive and likely to appear in targeted or opportunistic attacks soon after PoC release—historical patterns suggest rapid weaponization once reliable primitives are public. Treat the absence of confirmed exploitation as temporary and plan for the worst case. (feedly.com)

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Final analysis: balancing urgency and operational risk​

CVE‑2025‑53136 is a sober reminder that kernel security is brittle: a small coding change intended to fix one flaw can expose kernel internals if concurrent behavior isn’t exhaustively tested. The vulnerability is not a remote‑code execution bug by itself, but it materially lowers the bar for privilege escalation when combined with other kernel bugs. For defenders, the appropriate response is clear: treat the CVE as high‑impact to your trust model and prioritize mitigation accordingly.
Actionable priorities for every environment are straightforward: patch quickly, harden local execution and sandbox policies, and tune detection for the attack patterns described above. In parallel, defenders should update regression and fuzzing suites to include high‑frequency user/kernel concurrency tests, and bias release pipelines toward safety checks that detect transient writes of kernel-origin data into user buffers.
Organizations that act decisively now—by applying Microsoft’s patch when available, constraining local execution paths, and improving telemetry—will significantly reduce their risk of this CVE becoming the pivot that turns a local foothold into full domain compromise. (rapid7.com)

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CVE‑2025‑53136 is a practical, verifiable leak that compounds the perennial tension between performance optimizations and security correctness in kernel code. It demands an operational response: patch, harden, detect, and test—quickly and deliberately.

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Source: eSecurity Planet Windows 11 Patch Opens Kernel Leak CVE-2025-53136