In a recent bulletin, the Health Sector Cybersecurity Coordination Center (HC3) issued alerts cautioning healthcare organizations about two prevalent cyberattack tactics: email bombing and credential harvesting. These methods, highlighted in the HC3 sector alert dated March 12, 2024, highlight the ongoing cybersecurity challenges faced by the healthcare sector. Email bombing, also known as mail bomb or letter bomb attacks, involves inundating an email address or server with numerous messages, typically orchestrated by a botnet. This flood of emails, a type of Denial of Service (DoS) attack, aims to overwhelm the victim’s mailbox, rendering it unusable and preventing access to important communications. Healthcare and Public Health (HPH) organizations are particularly susceptible to such attacks, as evidenced by past incidents where cyber assailants targeted government email inboxes, causing significant disruptions.
The HC3 alert provides a comprehensive overview of email bombing techniques, highlighting various methods employed by malicious actors to disrupt healthcare organizations’ operations and compromise their security. These include registration bombs, which involve automated bots inundating recipients with numerous newsletter sign-ups simultaneously, resulting in an overwhelming influx of emails and potential exposure to spam and malware. Attachment attacks aim to overload server storage by sending multiple emails with large attachments, rendering systems unresponsive and impeding regular operations. Similarly, link listings involve signing up targeted email addresses for multiple subscription services, indirectly flooding inboxes with unwanted content and increasing the risk of exposure to malicious links or phishing attempts. Mass mailings, whether intentional or accidental, can overwhelm recipients with a barrage of emails, disrupting communication channels and preventing productivity. Reply-all assaults exacerbate the situation by flooding inboxes with responses to extensive email chains, often compounded by automated replies like out-of-office messages, further complicating email management and potentially exposing sensitive information. Zip bombs, in the form of large, compressed archive files, also present a unique threat by consuming server resources upon decompression, leading to degraded performance and potential downtime. Each of these techniques presents distinct challenges and risks to healthcare providers, emphasizing the importance of robust cybersecurity measures to mitigate such threats effectively.
In response to email bombing attacks, healthcare organizations are advised to take proactive measures, such as refraining from engaging with attackers, reporting incidents to IT or cybersecurity teams, reviewing account information for suspicious activities, contacting financial institutions in case of unauthorized transactions, changing passwords, and seeking assistance from email service providers. HC3 advises healthcare organizations to establish robust security policies that cover both user behavior and technical processes. This entails implementing measures to identify early signs of attacks, such as monitoring for unusual patterns or spikes in email traffic indicative of email bombing attempts. Staff should be educated comprehensively about the risks associated with email bombing and trained to recognize suspicious email activity promptly. Organizations are also encouraged to adopt confirmed opt-in processes for new sign-ups, requiring users to verify their email addresses via a unique link before receiving further communications. Integration of reCAPTCHA for verification purposes can further strengthen defenses by distinguishing between human users and automated bots, preventing malicious actors from inundating systems with fraudulent sign-ups. Leveraging the MITRE ATT&CK framework enables organizations to classify adversary tactics and techniques systematically, facilitating a more proactive and targeted approach to threat detection and response. By implementing these security measures collectively, healthcare organizations can strengthen their resilience against email bombing and other cyber threats, improving the overall security posture of their systems and data.
Another tactic highlighted in the HC3 alert is credential harvesting, which involves adversaries acquiring login credentials through diverse methods such as phishing attacks, procurement from third-party websites, or brute-force techniques aimed at guessing passwords. Once obtained, compromised credentials can serve as a gateway for perpetrators to conduct various nefarious activities within healthcare organizations’ networks. For example, adversaries may leverage these credentials to orchestrate sophisticated phishing campaigns, where they masquerade as legitimate entities to deceive unsuspecting users and extract sensitive information. Compromised credentials also enable unauthorized access to confidential data repositories, posing a grave threat to patient privacy and organizational security.
To effectively mitigate cyber threats, healthcare organizations must adopt a comprehensive strategy. This begins with educating staff members on cybersecurity best practices, ensuring they are equipped to recognize and respond to potential threats like email bombing and credential harvesting. Organizations should also conduct thorough assessments of their enterprise risk, identifying vulnerabilities in systems and processes vulnerable to exploitation. These assessments inform the prioritization of security measures and resource allocation. Developing tailored cybersecurity roadmaps is also necessary, outlining strategic plans to improve cybersecurity, implement robust security protocols, and establish incident response procedures aligned with organizational objectives. Leveraging resources such as the Cyber Hygiene Vulnerability Scanning services offered by the Cybersecurity & Infrastructure Security Agency (CISA) further strengthens defenses. These scanning services proactively identify and address security weaknesses in external networks, strengthening resilience against cyber threats when paired with regular vulnerability scans and prompt action on findings.
