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Author: CyberDudeBivash
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 Daily Threat Intel by CyberDudeBivash
Zero-days, exploit breakdowns, IOCs, detection rules & mitigation playbooks.

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 React2Shell Overview

React2Shell is an insecure deserialization vulnerability in the React Server Components ‘Flight’ protocol. Successful exploitation allows an unauthenticated attacker to execute arbitrary OS commands on the server (running in the context of the web server process, e.g., Node.js/Next.js).

Phase 1: Initial Exploitation & Reconnaissance IOCs

The initial compromise is typically a single, crafted HTTP request that triggers the RCE, often followed by a quick reconnaissance command.

1. Network & Web Server Log Indicators

2. File System Indicators (Exploitation Stage)

 Phase 2: Post-Exploitation & Malware Deployment IOCs

After RCE is achieved, attackers download and execute secondary payloads (like coin miners or backdoors).

3. File and Process Indicators (Malware)

4. Persistence Indicators

 Phase 3: Command & Control (C2) Communication IOCs

After installing the payload, the malware beacons out to a C2 server for instructions or to exfiltrate data.

5. Network Traffic Indicators

 Mitigation & Remediation Actions

The most critical step is patching the underlying vulnerability.

1. Immediate Actions

• Patch Immediately: Upgrade React Server Components to a patched version: 19.0.1, 19.1.2, or 19.2.1 (or later) to prevent RCE. Update frameworks like Next.js (App Router), Waku, etc., to their fixed versions.
• WAF/Network Block: Deploy Web Application Firewall (WAF) rules to detect and block suspicious POST requests, and block the C2 IP addresses listed above.

2. Remediation and Post-Patch Hunting

• Process Termination: Identify and terminate any suspicious processes, particularly xmrig, [ksoftirqd], or shells spawned directly by the Node.js/web server process.
• Secrets Rotation: Assume compromise of environment variables, API keys, database credentials, and any secrets stored in the application’s configuration. Rotate all of them immediately.
• Clean Rebuild: Rebuild and redeploy the affected workload from a clean image/source code after patching, instead of just cleaning the compromised system.

1) What to Hunt First (High-Confidence Behavioral IOCs)

A. Initial Access / Execution (Developer & “React” Lures)

Look for developer workflows being abused:

• Suspicious node.exe / npm / yarn / pnpm execution spawning shells
  • node.exe -> cmd.exe
  • node.exe -> powershell.exe
  • node.exe -> wscript.exe / cscript.exe
  • npm.exe -> powershell.exe
• Script execution from project folders
  • %USERPROFILE%\Documents\*
  • %USERPROFILE%\Desktop\*
  • C:\Users\<user>\AppData\Roaming\*
  • C:\Users\<user>\AppData\Local\Temp\*
  • C:\Users\<user>\AppData\Local\Microsoft\Windows\INetCache\*
• Suspicious install-time scripts in JS ecosystems (endpoint artifacts)
  • postinstall, preinstall, install, prepare scripts firing unexpectedly
  • Unknown binaries dropped during npm install

Windows Event / Sysmon signals

• Sysmon Event ID 1 (Process Create) with parent node.exe and child powershell.exe/cmd.exe
• Sysmon Event ID 11 (File Create) in AppData\Roaming, Temp, or hidden folders right after npm/yarn activity

2) Host IOCs (Persistence + Payload Staging)

A. Common Persistence Locations to Check

Startup folders

• C:\Users\<user>\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup\

Registry Run keys

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run
• HKLM\Software\Microsoft\Windows\CurrentVersion\Run

Scheduled Tasks

• Tasks with:
  • Random names (6–12 chars, mixed case)
  • Triggers: “At logon”, “On idle”
  • Action invoking powershell -enc, cmd /c, mshta, rundll32, or node

Services / WMI

• Newly created service with odd ImagePath
• WMI event subscription (rare but high value if present)

B. Typical Payload Staging Patterns (File IOCs)

Hunt for executables/scripts dropped under:

• %APPDATA%\ (Roaming)
• %LOCALAPPDATA%\
• %TEMP%\
• %ProgramData%\
• Hidden directories like:
  • %APPDATA%\<random>\
  • %LOCALAPPDATA%\<random>\
• Look for:
  • .js, .jse, .vbs, .ps1, .bat, .cmd
  • “double extensions” (e.g., update.pdf.exe, react_fix.png.scr)
  • Files with recent creation time matching the suspected install/launch window

3) Network IOCs (C2 + Exfil Patterns)

A. High-Signal Network Behaviors

• Node-based apps making outbound traffic to unusual hosts
  • node.exe initiating external connections (rare in many enterprise endpoints unless dev machines)
• DNS to newly registered domains or random subdomains
• HTTPS with odd User-Agents from powershell, node, curl, wget, or custom agents
• Beaconing
  • Small, periodic outbound requests (e.g., every 30s / 60s / 5m)
• Suspicious endpoints
  • /api/v1/gate, /panel, /connect, /update, /sync, /cdn/*
  • Requests carrying base64 blobs in headers, cookies, or URL params

B. Quick Network Hunt Filters

• Outbound connections from:
  • powershell.exe, cmd.exe, mshta.exe, rundll32.exe, wscript.exe, node.exe
• TLS SNI domains not seen before in your environment
• DNS queries followed immediately by connection attempts from the same host/user

4) Ready-to-Run Hunting Queries

A. Microsoft Defender for Endpoint (KQL)

1) Node spawning PowerShell / CMD

DeviceProcessEvents
| where InitiatingProcessFileName in~ ("node.exe","npm.exe","yarn.exe","pnpm.exe")
| where FileName in~ ("powershell.exe","cmd.exe","wscript.exe","cscript.exe","mshta.exe","rundll32.exe")
| project Timestamp, DeviceName, AccountName, InitiatingProcessFileName, InitiatingProcessCommandLine, FileName, ProcessCommandLine
| order by Timestamp desc

2) Suspicious encoded PowerShell launched from dev tooling

DeviceProcessEvents
| where FileName =~ "powershell.exe"
| where ProcessCommandLine has_any ("-enc","-encodedcommand","FromBase64String","IEX","Invoke-Expression")
| where InitiatingProcessFileName in~ ("node.exe","npm.exe","yarn.exe","pnpm.exe","cmd.exe")
| project Timestamp, DeviceName, AccountName, InitiatingProcessFileName, InitiatingProcessCommandLine, ProcessCommandLine
| order by Timestamp desc

3) New autoruns in common persistence paths

DeviceFileEvents
| where FolderPath has_any (@"\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup",
                           @"\ProgramData\",
                           @"\AppData\Roaming\",
                           @"\AppData\Local\Temp\")
| where ActionType in ("FileCreated","FileModified")
| where FileName endswith ".lnk" or FileName endswith ".ps1" or FileName endswith ".vbs" or FileName endswith ".js" or FileName endswith ".exe"
| project Timestamp, DeviceName, AccountName, FolderPath, FileName, SHA256
| order by Timestamp desc

4) Outbound connections from suspicious processes

DeviceNetworkEvents
| where InitiatingProcessFileName in~ ("powershell.exe","cmd.exe","mshta.exe","rundll32.exe","wscript.exe","node.exe")
| where RemoteUrl != "" or RemoteIP != ""
| project Timestamp, DeviceName, AccountName, InitiatingProcessFileName, InitiatingProcessCommandLine, RemoteUrl, RemoteIP, RemotePort
| order by Timestamp desc

B. Splunk (Windows + Sysmon)

1) Node → PowerShell / CMD (Sysmon EID 1)

index=windows sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=1
(ParentImage="*\\node.exe" OR ParentImage="*\\npm.exe" OR ParentImage="*\\yarn.exe" OR ParentImage="*\\pnpm.exe")
(Image="*\\powershell.exe" OR Image="*\\cmd.exe" OR Image="*\\wscript.exe" OR Image="*\\mshta.exe" OR Image="*\\rundll32.exe")
| table _time, Computer, User, ParentImage, ParentCommandLine, Image, CommandLine
| sort - _time

2) Encoded PowerShell

index=windows EventCode=1 sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational"
Image="*\\powershell.exe" (CommandLine="*-enc*" OR CommandLine="*-EncodedCommand*" OR CommandLine="*FromBase64String*" OR CommandLine="*IEX*")
| table _time, Computer, User, ParentImage, CommandLine
| sort - _time

5) “IOC Packs” You Should Compile (Fill These From Your Case)

When you confirm artifacts from one infected endpoint, build a pack:

A. File Hash IOCs

• SHA256: <malware_dropper_hash>
• SHA256: <stage2_hash>
• SHA256: <persistence_binary_hash>

B. Domain / IP IOCs

• Domains: <c2_domain_1>, <c2_domain_2>
• IPs: <remote_ip_1>, <remote_ip_2>
• URLs:
  • https://<domain>/api/<path>
  • https://<domain>/update/<path>

C. Process Command-Line IOCs

• Exact strings found in:
  • powershell -enc <blob>
  • cmd /c certutil -urlcache -split -f ...
  • mshta http(s)://...
  • node <temp>\*.js

6) Triage Workflow (Fast)

1. Start with one known-suspect machine

• Pull process tree around node/npm/yarn execution
• Identify child processes + command lines

2. Pivot on hashes + file paths

• Search enterprise-wide for same SHA256, same FolderPath, same FileName

3. Pivot on network

• Search for the same RemoteUrl/RemoteIP across the fleet
• Identify other hosts with identical beacon intervals

4. Confirm persistence

• Scheduled tasks + Run keys + Startup folder artifacts

5. Contain

• Isolate hosts
• Block domains/IPs
• Hunt laterally (credentials + token theft patterns)

CYBERDUDEBIVASH’S RECOMMENDATION :

. Patch Immediately (The Only Definitive Fix)

• Upgrade React Server Components (RSC) Packages: Update the vulnerable packages (react-server-dom-webpack, -parcel, and -turbopack) to the patched versions:
  • 19.0.1 (or later)
  • 19.1.2 (or later)
  • 19.2.1 (or later)
• Upgrade Next.js: If using the Next.js App Router, upgrade to a stable patched version immediately (e.g., 15.0.5, 16.0.7, or the latest patch release for your minor version).
• Update All RSC-Enabled Frameworks: Apply patches for any other affected frameworks using RSC, such as Waku, RedwoodSDK, React Router RSC preview, etc.

2. Hunting & Incident Response (Assume Breach)

Since exploitation is active in the wild and the vulnerability has a CVSS score of 10.0, assume publicly exposed systems are compromised.

• Hunt for IOCs: Use the Indicators of Compromise (IOCs) provided in the playbook above (and from vendor advisories) to scan your environment for signs of compromise, such as:
  • Unexpected processes (whoami, id, xmrig, [ksoftirqd], or shells) spawned directly by the Node.js/web server process.
  • Suspicious network connections to known C2 IP addresses.
  • Unexpected files written to the /tmp/ directory or hidden folders.
• Rotate Credentials: Immediately rotate all secrets, API keys, database credentials, and cloud credentials (e.g., AWS IAM keys) that were accessible to the compromised web server process/container environment.

3. Implement Layered Defenses (Interim Protection)

• WAF Rules: Deploy WAF rules as an interim layer of protection to block suspicious POST requests targeting RSC endpoints with malicious payloads. Do not rely on WAF alone—it can be bypassed.
• Network Monitoring: Enforce egress filtering to prevent the compromised web server/container from making unauthorized outbound connections to external hosts or cloud metadata endpoints (169.254.169.254).

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