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CyberDudeBivash Threat Intel | Government Targeting | Windows Priv-Esc

New Stealthy PowerShell Scripts Targeting Government Agencies + CVE-2025-29970 Microsoft “Brokering File System” Flaw Enabling SYSTEM Privileges

Author: CyberDudeBivash  |  Published: 23 Dec 2025 (IST)  |  Category: Threat Intel / Incident Response / Windows Security

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Table of Contents

1. TL;DR (Executive Snapshot)
2. Threat Story #1: Stealthy PowerShell Scripts Targeting Government Agencies
3. Attack Flow & Kill Chain (Fileless + Steganography Patterns)
4. Detections: Telemetry, SIEM Queries, Windows Logs
5. Mitigations: Hardening, Prevention, and Response Actions
6. Threat Story #2: CVE-2025-29970 “Brokering File System” SYSTEM Privilege Escalation
7. Patch Guidance, Exposure, and Validation Checklist
8. 30–60–90 Day Defensive Playbook
9. CyberDudeBivash Services & Apps (Lead CTAs)
10. FAQ
11. References
12. Hashtags

TL;DR (Executive Snapshot)

• Government-focused intrusions are increasingly “fileless”: recent reporting shows multi-stage phishing leading to stealthy PowerShell execution via WMI, in-memory payload loading, and hiding base64 data inside images using markers such as BaseStart- and -BaseEnd. (See Zscaler ThreatLabz and related analyses.) (Sources: Zscaler ThreatLabz, Cyble) 
• CVE-2025-29970 is a High severity local privilege escalation in Microsoft’s Brokering File System (use-after-free, CWE-416) with a Microsoft CVSS v3.1 base score of 7.8. Attackers with local access and low privileges can potentially escalate toward SYSTEM. 
• Action now: Patch Windows where applicable, restrict PowerShell, enable Script Block Logging, tighten WMI/Win32_Process creation telemetry, and hunt for suspicious image downloads followed by base64 extraction + reflection-based assembly loads. 

Threat Story #1: New Stealthy PowerShell Scripts Targeting Government Agencies

A recent wave of government-focused intrusion reporting highlights a tactic that keeps winning: attackers push victims through a staged infection chain where PowerShell does the “quiet work” in-memory. Instead of dropping obvious executables, the chain often ends with PowerShell fetching an image from the internet and extracting a base64-encoded payload hidden inside the file, then loading it as a .NET assembly without writing a traditional binary to disk. This is specifically documented in a spear-phishing campaign attributed to BlindEagle targeting a Colombian government agency, with PowerShell execution delivered in a stealthy, fileless manner and payload data embedded inside an image between recognizable markers. 

Operationally, this pattern is designed to defeat basic endpoint controls and bypass simplistic attachment scanning. The attacker’s goal is not just access—it’s quiet persistence and lateral movement inside a high-value environment where email trust relationships, internal accounts, and organizational workflows can be abused to increase delivery success.

CyberDudeBivash Analyst Note: When a threat actor chooses “image + hidden base64 + in-memory assembly load,” they’re optimizing for stealth and speed. That combination typically means you must rely on telemetry (process lineage, script block logs, network artifacts, and AMSI/ETW) rather than “file-based” detections alone.

Attack Flow & Kill Chain (Fileless + Steganography Patterns)

While exact artifacts differ per campaign, the documented flow in recent reporting follows a consistent blueprint:

1. Initial access: spear-phishing email crafted to look internal or authoritative, sometimes sent from a compromised account in the same organization. 
2. Stage loader: script/HTML/SVG or multi-step dropper to bootstrap execution and evade attachment controls.
3. Stealth execution: WMI is used to spawn PowerShell (e.g., via Win32_Process creation), minimizing visible windows and reducing user suspicion. 
4. Payload concealment: PowerShell downloads an image and extracts embedded data between markers such as BaseStart- and -BaseEnd. 
5. In-memory load: decoded content is loaded via reflection (e.g., Reflection.Assembly::Load) and executed directly in memory, minimizing disk artifacts. 
6. Post-exploitation: credential access, persistence, and C2 with further living-off-the-land techniques.

Why this matters for government networks: These environments often contain legacy endpoints, mixed logging maturity, and high trust in internal email. Attackers exploit those assumptions.

Detections: Telemetry, SIEM Queries, Windows Logs

Your detection strategy should focus on process lineage + PowerShell visibility + WMI eventing. Below are practical, SOC-ready signals to prioritize.

1) Process & Command-Line Red Flags

• Parent-child anomalies: Office apps, browsers, or scripting hosts spawning powershell.exe.
• Encoded commands: PowerShell with -EncodedCommand, -ExecutionPolicy Bypass, -NoProfile.
• Hidden window usage: flags suggesting minimized/hidden execution to reduce user awareness.

2) PowerShell Logging Must-Haves

• Script Block Logging: capture script content (high value for base64 extraction logic).
• Module Logging: capture loaded PowerShell modules.
• AMSI integration: ensure your EDR leverages AMSI where possible.

3) WMI Execution Hunting

• Look for WMI-based process creation consistent with “fileless” chains (e.g., process creation via WMI pathways). 
• Correlate WMI process creation with immediate outbound connections to unusual hosts, especially image fetches followed by PowerShell-heavy activity.

4) Network Signals (High Confidence)

• PowerShell contacting external repositories to fetch “benign-looking” images that become payload carriers. 
• Short burst download followed by no file writes but immediate .NET runtime activity (in-memory load pattern).

IOC Guidance: Because many campaigns rotate infrastructure rapidly, rely on behavior-based analytics. Use IOCs as “breadcrumbs,” not your primary detection control.

Mitigations: Hardening, Prevention, and Response Actions

Immediate (0–72 hours)

• Turn on PowerShell visibility: Script Block Logging + Module Logging in high-risk segments (government endpoints, finance, HR, executive assistants).
• Constrain PowerShell: enforce least privilege; reduce who can run full language mode; restrict script execution where operationally possible.
• Block common abuse patterns: tighten egress and block unknown destinations; watch for suspicious image downloads used as payload carriers. 
• Email defense: add extra controls for internal-to-internal email anomalies; monitor compromised internal accounts.

Short-Term (1–4 weeks)

• Attack surface reduction: disable legacy scripting where feasible; block macro abuse; harden Office spawning behavior.
• WMI governance: restrict WMI usage in user workstations; alert on process creation sequences consistent with fileless tradecraft. 
• Detection engineering: implement behavioral rules for “image download → base64 extract markers → reflection assembly load” patterns. 

Medium-Term (1–3 months)

• Zero Trust segmentation: limit lateral movement paths; reduce shared admin credentials.
• Continuous patching discipline: privileged escalation bugs become “finisher moves” after phishing—so keep Windows fully patched.
• Red-team simulations: simulate fileless PowerShell tradecraft in a lab and validate your detections.

Response trigger: If you see WMI-spawned PowerShell that downloads an image then runs reflection-based loads, treat it as a likely compromise and isolate fast.

Threat Story #2: CVE-2025-29970 — Microsoft “Brokering File System” Flaw Grants SYSTEM Privileges

CVE-2025-29970 is a Windows-related privilege escalation vulnerability described as a use-after-free in Microsoft’s Brokering File System. It allows an authorized attacker to elevate privileges locally. Microsoft’s CNA CVSS v3.1 score is 7.8 (High) with vector AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H, meaning it is not a remote bug by itself—but it is highly valuable after initial access (phishing, drive-by, stolen creds) to jump from low privilege to higher privileges.

In real-world attacker playbooks, local privilege escalation (LPE) flaws are often chained immediately after a foothold is obtained. That’s why LPE vulnerabilities matter even when the initial entry point is “just a phishing email” or a script-based loader: once the attacker lands code execution as a standard user, an LPE can transform that into a near-complete endpoint takeover.

Severity & Classification

• Type: Elevation of Privilege (Local)
• Root cause class: Use After Free (CWE-416)
• CVSS v3.1: 7.8 High (Microsoft CNA score)

Known Affected Platforms (as listed in NVD CPE notes)

NVD’s change history lists affected configurations including Windows Server 2022 (23H2), Windows Server 2025, and Windows 11 24H2 (arm64/x64) up to specific build exclusions. Use Microsoft update guidance and your patch management data to map exact build numbers in your fleet.

CyberDudeBivash Practical Risk View: Treat CVE-2025-29970 as a “post-compromise amplifier.” If your environment has active phishing or fileless PowerShell activity, this class of bug increases the probability of full endpoint control.

Patch Guidance, Exposure, and Validation Checklist

CVE-2025-29970 appears in May 2025 Patch Tuesday roundups from multiple security vendors and researchers. Use those as a starting point, then validate patch state via your endpoint inventory and update compliance. 

Validation Checklist (SOC + IT Ops)

1. Inventory: Identify all Windows 11 24H2 endpoints and Windows Server 2022/2025 builds in scope. 
2. Patch state: Confirm May 2025 security updates are installed (or later cumulative updates that supersede them). 
3. Privileged monitoring: On endpoints that cannot patch immediately, increase telemetry and apply additional restrictions to PowerShell and WMI.
4. Post-patch verification: Re-check build numbers and update KB presence through your endpoint management solution.
5. Threat hunting: Prioritize hunts where fileless PowerShell activity is observed—LPE exploit attempts may follow. 

Minimum bar: If a machine touches sensitive data, it must be patched fast. LPE vulnerabilities are frequently used to disable EDR, dump creds, and persist.

30–60–90 Day Defensive Playbook (Government-Grade)

Day 0–30: Stop the bleeding

• Patch: prioritize systems aligned with NVD-flagged configurations and May 2025 Windows patch rollups. 
• Enable PowerShell Script Block + Module logging in critical networks.
• Roll out behavioral detections for WMI-spawned PowerShell + “image payload” patterns. 

Day 31–60: Increase attacker cost

• Constrain scripting across non-admin users and sensitive endpoints.
• Harden email trust flows; add higher friction for suspicious internal senders and newly compromised accounts.
• Segment networks; reduce lateral paths from user subnets into admin/service zones.

Day 61–90: Prove resilience

• Run purple-team exercises simulating fileless PowerShell intrusion chains.
• Track MTTD/MTTR improvements and close logging gaps.
• Standardize “rapid isolation” and “credential reset” workflows for high-risk endpoints.

CyberDudeBivash Services & Apps

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FAQ

Is CVE-2025-29970 remotely exploitable?

The CVSS vector indicates local attack requirements (AV:L). In practice, attackers often chain local privilege escalation after they already gained initial access through phishing or another foothold. 

Why do attackers hide payloads inside images?

Images are common on networks, often permitted through filtering, and can carry encoded data that blends into normal traffic. Recent reporting describes base64 embedded between markers like BaseStart- and -BaseEnd, then loaded in-memory as a .NET assembly. 

What is the fastest detection win for fileless PowerShell attacks?

Enable Script Block Logging and correlate it with process creation telemetry (especially WMI-spawned PowerShell) and unusual outbound requests that fetch “benign-looking” files followed by reflection-based assembly loads.

References

• Zscaler ThreatLabz reporting on BlindEagle campaign targeting a Colombian government agency. 
• Cyble analysis describing base64 extraction between BaseStart- and -BaseEnd and in-memory .NET assembly loading.
• NVD entry for CVE-2025-29970 (description, CVSS 7.8, CWE-416, affected configuration notes).
• Rapid7 May 2025 Patch Tuesday roundup listing CVE-2025-29970. 
• Sophos Patch Tuesday coverage mentioning CVE-2025-29970 among Windows EoP issues. 
• Zero Day Initiative May 2025 security update review (contextual Microsoft update coverage). 

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