A public proof-of-concept (PoC) has been released for CVE-2026-39875, a macOS vulnerability affecting the Common UNIX Printing System (CUPS) that enables an unprivileged local attacker to perform arbitrary file writes with root privileges. The vulnerability impacts macOS Sonoma, Sequoia, and Tahoe versions prior to macOS 14.8.8, 15.7.8, and 26.6. Security researcher published the PoC, demonstrating that two logic flaws within the privileged cupsd printing daemon can be chained to abuse root-level file operations. While the PoC does not provide a direct interactive root shell, the ability to write files as root represents a significant privilege escalation risk and could potentially be leveraged to achieve full system compromise depending on the targeted files and system configuration.

The exploitation process involves an attacker first registering a malicious printer and capturing a valid CUPS authentication token during the printer probing process. The attacker can then replay this token to register another malicious printer configured with a file:// device URI, allowing the attacker to select a local file path that is not protected by System Integrity Protection (SIP). Due to improper validation timing, the CUPS daemon may perform privileged file operations before completing authentication checks. The attacker can then submit a crafted print job containing controlled data, causing the cupsd service running with root privileges to write attacker-controlled content to the selected location.

The publicly available PoC confirms that the vulnerability can be reproduced on affected macOS versions, including macOS Tahoe 26.4.1, Sequoia 15.7.5, and Sonoma 14.8.5, without requiring additional user interaction after execution. However, the researcher clarified that the script only demonstrates the creation of a root-owned file and does not automatically achieve complete privilege escalation. Despite this limitation, arbitrary root file write vulnerabilities are considered highly impactful because attackers with local access could abuse them to modify sensitive configuration files, persistence mechanisms, scheduled tasks, application support files, or other system resources to gain elevated privileges.

Apple has patched CVE-2026-39875 in macOS 26.6, macOS 15.7.8, and macOS 14.8.8, and organizations should prioritize applying these updates, especially on shared Mac environments, developer systems, and endpoints where untrusted local applications may execute. Security teams should monitor for suspicious printer registrations, unexpected CUPS configuration changes, unusual file-based printer destinations, and abnormal print job activity. Until all systems are patched, limiting unnecessary printer administration privileges and increasing monitoring of CUPS-related events can help reduce the risk of exploitation, as the availability of a public PoC increases the likelihood of active testing by attackers.