CVE-2025-59260: Mitigating Local Information Disclosure in Failover Cluster

Microsoft has confirmed CVE-2025-59260 as a local information‑disclosure vulnerability in the Microsoft Failover Cluster virtual driver that can write sensitive cluster state into log files or otherwise expose privileged configuration data to low‑privileged local actors, and Microsoft has published updates to address the defect.

Background​

Failover clustering and Storage Spaces Direct (S2D) are core Windows Server technologies used to provide high‑availability services, host virtual machine workloads, and underpin hyperconverged infrastructure. Cluster components run with elevated privileges and produce diagnostic traces and persisted logs that are used for troubleshooting, replication, and health monitoring. When those components inadvertently write secrets, tokens, GUIDs, connection strings, or kernel pointers into logs or return them to user contexts, the result is a classic information disclosure (CWE‑532) that can materially aid reconnaissance and follow‑on attacks.
Microsoft’s public advisory records CVE‑2025‑59260 as an information disclosure with a local attack vector and a CVSS v3.1 base score of 5.5 (Medium) using the vector string AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N — high confidentiality impact, no integrity or availability impact reported in the vendor vector. The vendor’s guidance and independent trackers consistently report that the vulnerability is local only and that vendor updates are available; administrators must map the CVE to the precise KB(s) for their installed Server build before claiming remediation. fileciteturn0file4turn0file17

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What we know (concise technical summary)​

• Affected component: Microsoft Failover Cluster / cluster virtual driver and related High Availability Services used in S2D/HCI and cluster hosts.
• Vulnerability class: Information disclosure (sensitive information unintentionally logged or returned to less‑privileged contexts).
• Attack vector: Local — an authenticated or local process must be able to interact with cluster services or read cluster log artifacts; remote network worming is not indicated.
• Privileges required: Low (non‑elevated/local accounts can trigger/read the outputs per published scoring).
• Impact: Confidentiality — High (leaked tokens, connection strings, or internal endpoints); Integrity/Availability reported as not impacted in the published CVSS vector.
• Exploit status: As of vendor disclosure and community trackers, no public proof‑of‑concept or confirmed in‑the‑wild exploitation has been broadly reported — but that absence does not reduce the operational urgency for affected, shared environments. fileciteturn0file1turn0file15

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Why an information‑disclosure in a cluster driver matters​

Failover Cluster services and S2D manage privileged state across nodes. Logs and diagnostic dumps produced during normal operations often contain:

• Administrative configuration and state dumps.
• Resource names, connection strings, endpoints, and temporary filesystem paths.
• Diagnostic messages that may include snippets of memory or partially redacted tokens and GUIDs.

Even small fragments — a GUID, partial token, or service account name — can shorten attacker reconnaissance and enable credential theft, lateral movement, or privilege escalation chains. In large estates where cluster nodes host multiple tenants (VDI, RDS, hyperconverged VMs), a low‑privilege local account or a compromised service may have the necessary access to harvest these logs. The real‑world operational risk therefore often exceeds the numeric CVSS rating because CVSS does not capture environment‑specific factors like shared admin workstations or permissive ACLs on cluster log files. fileciteturn0file8turn0file7

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Likely root causes (based on patterns from similar CVEs)​

Microsoft’s public advisory intentionally omits low‑level implementation details; however, historically similar kernel and driver info‑leaks arise from a small set of recurring mistakes:

• Returning uninitialized or partially initialized buffers to user mode (leftover kernel memory copied to user buffers).
• Incorrectly reporting returned lengths in IOCTL or RPC handlers (driver claims N bytes written while only M bytes were filled).
• Excessive diagnostic logging without redaction of sensitive fields.
• Insufficient validation of management API inputs or reparse‑point parsing that leads to out‑of‑bounds reads.

Until a researcher or Microsoft publishes a formal technical breakdown, any specific root‑cause claim is provisional. Administrators should assume any of these patterns are possible and act accordingly. fileciteturn0file9turn0file3

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Realistic attack scenarios and threat models​

The information‑disclosure classification lends itself to several practical attack patterns:

• Low‑privilege local user reads cluster logs
• Scenario: A contractor, build agent, or developer account with shell access to a cluster node copies cluster log files and extracts connection strings, GUIDs, or partial token fragments.
• Impact: These artifacts accelerate lateral movement and credential abuse.
• Malicious insider or rogue admin
• Scenario: An internal actor with limited but legitimate access purposefully searches logs for mislogged secrets and exfiltrates sensitive configuration.
• Impact: Direct exfiltration of configuration and credentials; harder to detect because activities originate from permitted hosts.
• Chaining with other vulnerabilities
• Scenario: Harvested secrets or endpoints are used to attack management APIs, exploit network‑facing services, or weaponize other local vulnerabilities (RCE/EoP).
• Impact: A local information leak becomes a stepping stone to full host compromise.

Because exploitation is local, environments with shared admin workstations, permissive local ACLs on logs, or long log retention windows are at substantially higher risk.

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Verification, confidence, and what to trust​

• Microsoft’s Security Update Guide entry is the canonical source for CVE→KB→build mappings and official remediation instructions. Administrators must consult that vendor page from a secure administrative workstation to capture the exact KB numbers for their Server SKUs.
• Multiple independent vulnerability aggregators and community summaries converge on the same high‑level facts (local information disclosure; CVSS 5.5; fix available), increasing confidence in both the existence and general classification of the bug. However, third‑party feeds may temporarily show provisional KB mappings that must be cross‑checked against Microsoft’s authoritative entries. fileciteturn0file4turn0file17
• Public technical write‑ups and proof‑of‑concepts are limited at disclosure. Treat any community technical reconstruction as provisional until corroborated by Microsoft or vetted researchers. This conservative stance reduces false positives in detection and prevents mistaken signature/IOCTL blocking based on incomplete analysis.

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Immediate remediation: a 0–72 hour operational playbook​

• Inventory and scope (0–6 hours)
• Use your management tooling (WSUS, SCCM/ConfigMgr, Intune, or third‑party EPM) to enumerate all hosts running Failover Cluster roles, S2D, and HCI components. Collect exact build strings for each host.
• Confirm vendor KBs (0–12 hours)
• From a secure admin workstation, open Microsoft’s Security Update Guide entry for CVE‑2025‑59260 and record the precise KB(s) that map to your Server builds; do not rely solely on third‑party aggregators for KB mappings.
• Patch staging and validation (12–48 hours)
• Test the published updates in a controlled ring (test → pilot → production). Validate cluster service health after patching and reboots. Confirm installation via Get‑HotFix or Windows Update history.
• Compensating controls if patching delayed (24–72 hours)
• Restrict local logins to cluster nodes: remove unneeded local accounts and require jump hosts with multi‑factor authentication for cluster management.
• Harden ACLs on cluster log directories to prevent low‑privilege reads. Rotate and inspect archived logs that predate the patch. fileciteturn0file4turn0file16
• Post‑patch hygiene (24–72+ hours)
• Rotate service account passwords, tokens, certificates, and connection strings if there is any plausible suspicion they were logged prior to remediation. Sanitize or securely delete historic logs that may contain sensitive artifacts.
• Forensics and containment (if suspicious activity is found)
• Preserve volatile memory, collect EDR telemetry and process dumps, and perform focused triage on a representative set of nodes. If evidence of compromise exists, rebuild from known‑good images after completing root‑cause analysis.

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Detection, hunting, and monitoring recommendations​

Because the vulnerability is a local information leak, detection and hunting should focus on who reads or interacts with cluster artifacts:

• Add SIEM/EDR rules to alert on non‑admin process reads of cluster log paths (for example, reads where InitiatingProcessAccountName is not SYSTEM or a designated admin account).
• Monitor for anomalous or repeated IOCTL or RPC activity against cluster management binaries originating from low‑privileged contexts. Correlate these with process creation events and outbound network activity that could indicate exfiltration.
• Baseline normal access patterns to cluster directories immediately after patching, then treat deviations in post‑patch windows as higher‑priority alerts.
• Hunt for sequences where low‑privilege processes copy or compress cluster logs before network activity, as this pattern can indicate staged exfiltration.

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Long‑term hardening (beyond the immediate patch)​

• Enforce least‑privilege on cluster nodes: limit local admin accounts, use role‑based access, and deploy purpose‑scoped service accounts for management tooling.
• Segregate administrative networks and require guarded jump hosts with MFA for all cluster administration. Isolate management APIs and restrict who can mount or inspect cluster resource disks.
• Redact and limit logging: implement log‑sanitization at source where possible, alter diagnostic verbosity to avoid emitting secrets, and encrypt archived logs. Adopt retention policies that minimize the window of exposure.
• Integrate file‑access telemetry into EDR/SIEM for critical directories and treat non‑admin reads as high‑priority alerts. This compensates for the fact that code fixes cannot retroactively sanitize historic logs.

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Operational risk assessment and scoring caveats​

• CVSS captures technical dimensions of a vulnerability but does not reflect environmental context. A Medium (5.5) score is accurate under the CVSS vector for a local attack but understates business risk for clusters that permit broad local user access, shared admin workstations, or long log retention windows. Operational risk is a function of both the vulnerability and the environment’s access controls. fileciteturn0file7turn0file8
• Patching eliminates the code defect going forward but does not remediate historical leakage; credential rotation and log sanitization are mandatory follow‑ups for hosts that may have logged sensitive artifacts.
• The lack of a public proof‑of‑concept reduces the risk of mass automated exploitation in the near term, but information disclosure bugs are frequently used silently as reconnaissance primitives and are therefore valuable to attackers conducting targeted compromises. Treat absence of PoC as not safe — prioritize remediation when the environment exposes the vector. fileciteturn0file1turn0file12

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Practical checklist (one page, for operations)​

• Inventory cluster nodes and capture exact OS build numbers.
• Retrieve the CVE entry from Microsoft’s Security Update Guide using a secure admin station and record KB→build mappings.
• Stage and deploy patches (test → pilot → prod), validate cluster health post‑reboot.
• Harden ACLs on cluster log and diagnostic directories; restrict local logins while patching.
• Rotate credentials/tokens/certificates that may have been logged; sanitize or delete archived logs containing secrets.
• Deploy SIEM/EDR rules to detect non‑admin reads of cluster logs and anomalous IOCTL/RPC patterns.

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Final analysis — strengths, weaknesses, and residual risks​

Strengths

• Microsoft has acknowledged and published an update for CVE‑2025‑59260, giving administrators a concrete remediation path and authoritative KB mapping source to reference.
• Community trackers and independent write‑ups converge on the same high‑level impact and guidance, allowing defenders to adopt a common operational playbook quickly.

Weaknesses / risks

• The vendor advisory omits detailed low‑level mechanics and IOCTL identifiers; defenders lacking precise code paths may struggle to craft deterministic detection signatures or block rules without risking false positives.
• Patching does not remove historically leaked secrets. Organizations must perform secrets hygiene and targeted forensic review where applicable. That operational burden amplifies remediation costs and complicates compliance reporting.

Residual risks

• Shared or multi‑tenant cluster hosts and management workstations remain highest risk until both code and operational controls (ACLs, admin separation, log hygiene) are enforced.
• If credentials or tokens were logged and later reused, a full threat lifecycle analysis — including token revocation and rotation — is required to reduce residual exposure.

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Microsoft’s CVE‑2025‑59260 advisory is a clear operational reminder: code fixes are necessary but not sufficient. For cluster and HCI operators, the right response combines prompt patching, targeted detection for non‑admin access to cluster telemetry, rotation of any possibly leaked secrets, and long‑term changes to logging and administrative controls so that secrets are never written where untrusted actors can read them. fileciteturn0file16turn0file12
Conclusion: apply the vendor patches now, verify KB→build mappings from Microsoft’s Security Update Guide, harden local access and log ACLs, rotate suspected secrets, and add SIEM/EDR rules to detect non‑admin reads of cluster logs — those steps will substantially reduce the real business risk posed by this local information‑disclosure vulnerability. fileciteturn0file15turn0file4

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Source: MSRC Security Update Guide - Microsoft Security Response Center