Threat Advisory: Critical Remote Code Execution Vulnerability in Common Unix Printing System (CUPS)

Overview: A newly reported vulnerability in the Common Unix Printing System (CUPS) poses a significant security threat to UNIX-based systems, including Linux and macOS. Security researcher Simone Margaritelli has published the first of a series of blog posts detailing the issue, which can be exploited by sending a specially crafted HTTP request to the CUPS service. This vulnerability allows remote attackers to gain access to affected systems and execute arbitrary code, potentially escalating privileges and compromising critical assets.

Threat Topography:

• Threat Type: Remote Code Execution (RCE) vulnerability in the CUPS service
• Industries Impacted: A wide range of industries using UNIX-based systems, including finance, healthcare, and government
• Geolocation: Global impact, targeting UNIX-based systems worldwide
• Environment Impact: High severity, enabling remote access and arbitrary code execution on vulnerable systems

Key Findings:

• The vulnerability affects multiple UNIX-based operating systems, including Linux and macOS.
• All versions of Red Hat Enterprise Linux (RHEL) are impacted but are not vulnerable by default.
• The exploit involves sending a specially crafted HTTP request to the CUPS service.
• Attackers can gain remote access to systems, execute arbitrary code, and potentially escalate privileges.
• The vulnerability has a high severity score and poses significant risk to organisations relying on UNIX-based systems.

Mitigations/Recommendations:

• Temporarily disable the CUPS service if not in use.
• Restrict access to the CUPS web interface to trusted networks only.

• For systems that cannot be updated or rely on the CUPS service, block all traffic to UDP port 631 and DNS-SD traffic (excludes zeroconf).

• Use network segmentation and strict access controls to limit the spread of potential attacks.

• Ensure other vulnerabilities are identified and remediated by running comprehensive vulnerability scans and tests.

• Ensure robust incident response and disaster recovery plans are in place to mitigate damage in the event of an exploit.

CVE Designations:

• CVE-2024-47176 (Reserved)
• CVE-2024-47076 (Reserved)
• CVE-2024-47175 (Reserved)
• CVE-2024-47177 (Reserved)

This vulnerability in CUPS is a significant threat to UNIX-based systems globally, with the potential for severe impact if exploited. Organisations using Linux, macOS, or other UNIX-based systems should take immediate action to disable or restrict access to CUPS, block vulnerable ports, and apply strong security controls. Monitoring for updates and preparing to patch systems as more information becomes available will be crucial in the coming days.
Stay tuned for further updates as more details are disclosed.

Reduce the risk:

 In Integrity360's view, the newly reported CUPS vulnerability is undoubtedly severe, but certain factors significantly reduce the overall risk:

• Not Always Vulnerable by Default - In systems like Red Hat Enterprise Linux, while all versions are affected, the vulnerability is not exposed in its default configuration, reducing the likelihood of immediate risk in many environments.
• Uncommon External Exposure of Port 631 - CUPS, which typically runs on port 631 for printing services, is rarely exposed to the internet in most environments. This greatly reduces the attack surface, as an attacker would likely need to be within the network to exploit the vulnerability.
• Targeted Network Access Required - Exploiting this vulnerability requires network access, meaning that only environments where CUPS is actively used and potentially misconfigured are at risk. In environments with strong network segmentation, access controls, and security measures, the risk of exploitation is notably reduced.
• Workarounds Available - Mitigations such as disabling the CUPS service or blocking access to port 631 can further reduce exposure, providing immediate steps to minimize risk while waiting for a formal patch.

Despite these mitigating factors, the potential for remote code execution and privilege escalation means that organisations with CUPS in use should still treat this vulnerability as critical, particularly in high-value networks where even internal threats pose significant risks.