Brother Printer Vulnerability: Unpatchable Default Admin Password Flaw Affects 689 Models

A critical vulnerability affecting 689 Brother printer models, along with devices from Fujifilm, Toshiba, and Konica Minolta, exposes default administrator passwords that can be remotely generated by attackers. The flaw, designated as CVE-2024-51978 (CVSS 9.8), cannot be patched via firmware updates, requiring hardware redesigns for a permanent fix¹. This article provides a technical breakdown of the vulnerability, its implications, and mitigation strategies for affected organizations.

Executive Summary for CISOs

The vulnerability allows attackers to derive default admin passwords using the device’s serial number, potentially compromising network integrity. Over 800,000 printers globally are exposed via port 9100, with Brother confirming that firmware updates cannot resolve the core issue². Enterprises must prioritize segmentation and password changes, while home users should follow Brother’s recommended reset procedures.

• Affected Vendors: Brother (689 models), Fujifilm, Toshiba, Konica Minolta
• Key CVEs: CVE-2024-51978 (password flaw), CVE-2024-51977 (data leak), CVE-2024-51979 (RCE)
• Mitigation: Password changes, network segmentation, firmware updates for secondary flaws

Technical Analysis of the Vulnerability

The primary flaw (CVE-2024-51978) stems from a predictable password generation algorithm tied to device serial numbers. Researchers speculate the default password follows patterns like "BR" + serial[-4:] + "!", though Brother has not disclosed the exact formula³. Attackers can exploit this via port 9100 (JetDirect) or through secondary vulnerabilities like CVE-2024-51979, a stack buffer overflow enabling remote code execution.

Brother’s advisory confirms that common default passwords include “initpass” or device-labeled “Pwd”. Resetting these requires a network factory reset if credentials are forgotten, a process detailed in Brother’s support documentation⁴. The inability to patch the flaw via firmware leaves organizations reliant on workarounds such as VLAN segmentation and disabling unused protocols (e.g., Telnet, FTP).

Mitigation Strategies

For enterprises, immediate actions should include:

1. Changing default admin passwords via the printer’s web interface (Settings > Security > Admin Password)
2. Segmenting printers onto secure VLANs and monitoring for anomalous traffic
3. Applying firmware updates for secondary flaws (e.g., CVE-2024-51979)

Home users are advised to perform a network factory reset (Settings > All Settings > Network > Network Reset) and disable IPv6 if unused⁵. Brother’s support portal provides model-specific firmware updates, though these do not address the serial-number flaw.

Relevance to Security Professionals

Red teams can leverage this vulnerability for network pivoting, while blue teams should prioritize detecting unauthorized access attempts to printer admin interfaces. SOC analysts should monitor for:

• Unusual traffic on port 9100/TCP
• Failed login attempts to printer web interfaces
• MAC address spoofing targeting printer VLANs

Threat intelligence researchers note that this flaw is particularly concerning for healthcare and financial sectors, where printers often handle sensitive documents. The lack of a firmware fix underscores the need for hardware-based security reviews in IoT devices.

Conclusion

The Brother printer vulnerability highlights systemic risks in embedded device security, particularly when flaws require hardware revisions. Organizations should treat affected printers as potential entry points for attackers and implement layered defenses. Future procurement should prioritize vendors with transparent security practices and patchable architectures.

References

1. “Millions of Brother Printers Contain Critical, Unpatchable Bug,” Dark Reading, Jun. 25, 2025. [Online]. Available: https://www.darkreading.com/endpoint-security/millions-brother-printers-critical-unpatchable-bug
2. “Brother Printer Default Passwords: Identification and Change,” The Word Network, May 3, 2025. [Online]. Available: https://www.thewordnetwork.org/brother-printer-default-passwords-identification-and-change
3. Brother Industries, “Admin Password FAQ,” Brother Support. [Online]. Available: https://support.brother.com/g/b/faqend.aspx?c=us&lang=en&prod=lmgroup1&faqid=faqp00100620_000
4. “Brother Printer Hacks: 689 Models Affected,” CyberShack. [Online]. Available: https://cybershack.com.au/computer/brother-printer-hacks-689-models-affected
5. Reddit Thread on Brother Printer Default Passwords. [Online]. Available: https://www.reddit.com/r/printers/comments/gonrko/new_brother_printer_default_passwords_do_not_work