CVE-2025-47979: Mitigating Information Disclosure in Windows Failover Cluster Logs

Microsoft has published an advisory for CVE-2025-47979, an information‑disclosure vulnerability in the Windows Failover Cluster service that can cause sensitive cluster data to be written to accessible log files, creating a local, low‑privilege attack path that should be treated as operationally significant despite a middling CVSS score.

Background​

Failover clustering is a core Windows Server capability used to keep services, virtual machines and storage highly available across multiple nodes. Clustering services run with elevated privileges and routinely produce detailed diagnostic data to traces and persistent log files; when that telemetry includes sensitive values (connection strings, tokens, or configuration fragments) and those logs are readable by low‑privilege accounts, the result is an information‑disclosure vulnerability with outsized operational consequences.
Microsoft has listed CVE‑2025‑47979 in its Security Update Guide and assigned a CVSS v3.1 base score of 5.5 (Medium). That score reflects a local attack vector and a confidentiality‑only impact—Integrity and Availability are not reported as affected—yet multiple community analyses underscore that the practical business risk can be high if logs contain service credentials or tokens.

---

What the vulnerability actually is​

Technical summary​

• Vulnerability type: Information disclosure / Sensitive information written to logs (CWE‑532).
• Affected component: Windows Failover Cluster logging/diagnostic paths.
• Attack vector: Local — an actor with some local access or the ability to read cluster logs can extract sensitive material.
• Impact: Confidentiality — secret or sensitive data may be disclosed; Integrity and Availability are not indicated.
• CVSS v3.1 base score: 5.5 (Medium) as published in vendor and aggregator records.

This is not a remote code execution or memory‑corruption flaw; it is a logging/design defect where cluster components write more information than they should into persistent logs that are accessible to actors who should not see those values. The root class is straightforward — the cluster wrote secrets into a file — but the downstream effects can be complex, especially in environments where local accounts or shared admin workstations exist.

What types of data are at risk​

Failover Cluster logs commonly record operational state, diagnostics and error traces. The kinds of artifacts that could appear in mislogged entries include:

• Administrative configuration dumps and cluster resource identifiers.
• Resource names, connection strings, and endpoint URIs.
• Paths or temporary filenames referencing privileged locations.
• Diagnostic strings that can inadvertently include tokens, GUIDs or fragments of sensitive state.

Any one of these artifacts can materially accelerate reconnaissance or follow‑on attacks if harvested by an attacker with local access.

---

How serious is this? Interpreting the CVSS and real risk​

A CVSS base score of 5.5 places CVE‑2025‑47979 in the Medium severity bucket, primarily because the attack requires local access. However, several operational factors can make the practical risk much higher than the score suggests:

• Privileged context of cluster components — clustering code runs in elevated contexts and therefore touches high‑value state.
• Shared admin workstations and non‑segregated management networks increase the likelihood a low‑privilege user can reach logs.
• Long log retention policies mean historical logs could contain sensitive entries written before the patch was applied; patching does not retroactively sanitize existing files.

Security practitioners should therefore treat this as an operational urgency where context (who can read cluster logs, how logs are protected, and whether secrets are present in logs) determines prioritization more than the numeric CVSS figure.

---

Attack scenarios and realistic threat models​

1. Low‑privilege local user reads logs​

A contractor, developer, or compromised service account with a shell on a cluster node reads or copies cluster log files and exfiltrates sensitive lines. The harvested artifacts — service account names, resource identifiers, partial tokens — are then used to escalate and pivot. This is the canonical and most straightforward scenario.

2. Malicious insider / rogue administrator​

An internal actor with legitimate but limited local access intentionally searches logs for mislogged secrets. Because admins often have access to clusters, the ability to persistently read logs can lead to targeted exfiltration of configuration or credential information.

3. Chaining with other vulnerabilities​

An attacker may combine log‑harvested artifacts with other flaws (RCE, EoP, misconfigurations) to achieve lateral movement or full compromise. Even small leaks can dramatically lower the cost of subsequent attacks by revealing endpoints, account names, or token fragments.
Key takeaway: because the vector is local, organizations that permit broad local access or use shared admin tools are at much higher risk than tightly segmented environments.

---

What Microsoft says and why you must confirm the KB mapping​

Microsoft’s Security Update Guide lists CVE‑2025‑47979 and provides the official KB mappings for the fixed builds. Community analyses repeatedly stress that the Update Guide is the authoritative source for exact KB article numbers and the correct cumulative update or security-only rollup to apply for each Windows Server SKU. Because the Update Guide is delivered as a dynamic web application, it sometimes requires an interactive browser to render correctly; administrators should therefore consult it from a secure admin workstation and record the KB(s) that map to their specific Windows Server builds.
Note of caution: third‑party vulnerability trackers occasionally publish CVE→KB mappings before Microsoft fully populates the Update Guide. If an external scanner or feed reports a KB mapping that differs from MSRC, treat it as unverified until you confirm the information against Microsoft’s Security Update Guide and the Microsoft Update Catalog.

---

Immediate action checklist (first 24–72 hours)​

• Confirm applicability: use Microsoft’s Security Update Guide entry for CVE‑2025‑47979 and capture the KB article numbers for your Windows Server SKUs. Do this from a secured administrative workstation.
• Inventory cluster nodes: identify all nodes running Failover Cluster roles and enumerate who has local accounts on those nodes. Use PowerShell and your asset management tooling to create a prioritized target set.
• Limit local access: remove or restrict non‑essential local accounts on cluster nodes; enforce unique admin accounts and jump‑box usage for management.
• Patch: apply the exact KB(s) Microsoft lists for your build in a staged manner (test → pilot → production). Validate installations using Get‑HotFix or Windows Update history.
• Sanitize historical logs: rotate or securely delete archived logs that could contain sensitive entries written prior to the patch. Rotating logs and secure wiping is necessary because patching does not remove data already written to disk.
• Rotate exposed secrets: where feasible, rotate service credentials, certificates and tokens that might plausibly have been recorded in logs. Prioritize those whose rotation is low‑cost and high‑impact.

---

Detection, monitoring and longer‑term mitigations​

Monitoring and SIEM use cases​

• Ingest file‑access events for cluster log directories (e.g., C:\Windows\Cluster*) into your SIEM and alert on non‑admin reads.
• Correlate file reads with user context and process parentage to spot suspicious access patterns.
• Create hunts for anomalous cluster management activity following unexpected log reads. Example detection logic can be implemented in Kusto or EDR query languages to flag reads by non‑administrator principals.

Hardening recommendations (longer term)​

• Enforce least privilege for cluster operations and dedicated service accounts with minimal rights.
• Segregate administrative functions onto jump boxes and restrict management network access to a hardened administrative VLAN.
• Revisit logging levels and scrub/redact sensitive fields at the source where possible — design logs to avoid capturing secrets.
• Implement log retention policies and secure storage for logs (restrict direct access, use encrypted archives, and apply role‑based access controls).

---

Operational caveats and verifiability notes​

• There is no public proof‑of‑concept or known in‑the‑wild exploitation recorded at the time of the advisory’s publication, according to published trackers and the Microsoft entry. However, absence of observed exploitation is not evidence of absence—local vectors are often harder to detect.
• Public feeds and third‑party aggregators may initially disagree on precise CVE→KB mappings; always reconcile against Microsoft’s Security Update Guide and the Microsoft Update Catalog to avoid mis‑patching.
• Applying the patch does not sanitize logs written before the fix; admins must treat historical logs as potentially sensitive and take remediation steps accordingly.

These caveats matter because they affect prioritization: if your environment contains shared admin workstations, legacy retention windows or multi‑tenant clusters, the risk of exploitation and impact of residual data is meaningfully higher.

---

Why logging design matters — a deeper analysis​

Logging is essential for troubleshooting and compliance, but it is also a persistent source of data exfiltration risk when developers or subsystems do not follow redaction or access control principles. CVE‑2025‑47979 highlights several recurring operational mistakes:

• Logging sensitive values by default during high‑verbosity diagnostics without gating or redaction.
• Inadequate ACLs on log directories that permit non‑admin reads on cluster nodes.
• Reliance on perimeter controls and a false assumption that “local” attack vectors are low risk. Perimeter defenses cannot prevent an actor who already has local read access to logs.

Fixing the underlying code will prevent new entries from being written, but true remediation requires improving the people and process aspects of logging: who can access logs, how long logs are retained, and what is recorded in them. These are the controls that turn a fix into a durable reduction in enterprise risk.

---

Practical playbook for administrators (step‑by‑step)​

• Identify affected systems:
• Run inventory queries to find all cluster nodes and their OS/build. Use Get-Cluster and Get-HotFix to collect evidence.
• Confirm vendor KBs:
• Open Microsoft’s Security Update Guide for CVE‑2025‑47979 from a secure admin workstation and record the KB numbers for each SKU.
• Patch in rings:
• Deploy updates to test clusters first, validate failover behavior and cluster health, then stage through pilot and production rings.
• Harden log access:
• Apply ACLs to cluster log directories, ensuring only required admin accounts have read/write permission. Monitor for exceptions.
• Sanitize and rotate logs:
• Remove or securely archive pre‑patch logs, perform secure deletion if those logs contain verified secrets, and update retention policies to minimize risk.
• Rotate secrets where feasible:
• Replace service credentials or keys reasonably suspected to have been logged. Prioritize credentials whose compromise would be high impact and low cost to rotate.
• Implement detection:
• Add SIEM rules and EDR telemetry to detect non‑admin reads and suspicious cluster admin actions. Use the initial days after patching to baseline normal access patterns.

---

Strengths and weaknesses of the response ecosystem​

Strengths:

• Microsoft published an advisory and assigned a CVE, enabling targeted remediation and vendor‑backed KB mapping.
• Community trackers and threat feeds corroborate the severity profile and emphasize operational steps such as log sanitation and access governance.

Weaknesses and operational risks:

• The dynamic nature of Microsoft’s Update Guide and inconsistent third‑party CVE→KB mappings during fast patch cycles can create confusion and mis‑patching risk. Administrators must validate the exact KB(s) for their SKU.
• Patching alone does not remove historical exposures: log hygiene and secret‑rotation are required to close residual gaps.

---

Conclusion​

CVE‑2025‑47979 is a reminder that log hygiene and access governance are security controls, not mere operational conveniences. While the vulnerability’s CVSS score is Medium (5.5), the combination of privileged logging contexts and local‑readable log files can turn a local information leak into the first step of a high‑impact enterprise compromise. Administrators should:

• Confirm applicability and exact KBs via Microsoft’s Security Update Guide on a secure admin workstation;
• Patch cluster nodes promptly in a staged manner;
• Sanitize or rotate historical logs and rotate exposed credentials where practical;
• Harden local access, implement SIEM detection for non‑admin log reads, and revise logging practices to avoid recording secrets.

Patching closes the code defect, but full remediation depends on improving operational controls that govern who can see cluster telemetry, how long logs are kept, and what is permitted to appear in the logs in the first place. Treat CVE‑2025‑47979 as a practical operational priority for any environment where cluster log access is not tightly controlled.

---

Source: MSRC Security Update Guide - Microsoft Security Response Center