Public PoC Released for macOS CUPS Vulnerability Enabling Root Privilege Escalation
A public proof-of-concept exploit is now available for CVE-2026-39875, a critical vulnerability in macOS's Common UNIX Printing System (CUPS) that allows local privilege escalation to root.
A public proof-of-concept (PoC) exploit has been released for CVE-2026-39875, a critical vulnerability affecting the Common UNIX Printing System (CUPS) on macOS. This flaw permits an unprivileged local user to achieve arbitrary file writes with root privileges, posing a significant risk to system integrity.
The vulnerability, which impacts macOS Sonoma, Sequoia, and Tahoe versions prior to specific patch levels (macOS 14.8.8, 15.7.8, and 26.6), was detailed by security researcher Dallas Dubs. The PoC demonstrates how two logic flaws within the privileged cupsd daemon can be chained together. While the exploit doesn't directly yield an interactive root shell, the ability to write arbitrary files as root provides a potent mechanism for local privilege escalation, especially when targeting critical system files or configurations.
The attack vector involves a local attacker first registering a malicious printer. During the printer probing phase, the attacker can steal a valid CUPS authentication token. This captured token is then replayed to register another printer, this time utilizing a file:// device URI. This URI targets a local path chosen by the attacker, which is not protected by System Integrity Protection (SIP), allowing the malicious write operation.
A critical aspect of this vulnerability is that the cupsd daemon may initiate root-privileged file operations before the authentication validation process is fully complete. In the final stage of the exploit, the attacker submits a crafted print job. The cupsd daemon then writes the attacker-controlled content to the selected file location with root privileges.
According to the PoC documentation, the attack requires no user interaction once initiated and has been successfully reproduced on vulnerable versions of macOS Sonoma, Sequoia, and Tahoe. The provided exploit script verifies the creation of a file with root ownership, confirming the arbitrary file write capability. While not a complete privilege escalation chain on its own, this primitive is highly impactful.
An attacker with existing local access could leverage this arbitrary root file write to modify insecurely handled configuration files, alter scheduled task definitions, compromise application support files, or exploit other writable locations. The ultimate impact depends on factors such as SIP restrictions, file permissions, endpoint security controls, and the attacker's ability to convert the file write into persistent root-level code execution.
Apple has addressed this vulnerability by releasing patches in macOS 26.6, macOS 15.7.8, and macOS 14.8.8. Organizations are strongly advised to prioritize the deployment of these updates, particularly on shared Mac systems, developer workstations, and any device where local code execution is possible. Security teams should also implement monitoring for unusual local printer registrations, modifications to printer device URIs, and suspicious print jobs targeting file destinations.
The public release of a PoC significantly increases the likelihood of active exploitation attempts. Prompt patching is therefore essential to mitigate the risk posed by CVE-2026-39875, ensuring the security of macOS environments against local privilege escalation threats.