Working exploit code is circulating for a bug in the printing system built into macOS, and it lets any user who is already on the machine write files anywhere on disk with root privileges.
The flaw is tracked as CVE-2026-39875 and sits in CUPS, the Common UNIX Printing System that Apple ships with macOS. It affects macOS Sonoma, Sequoia and Tahoe before versions 14.8.8, 15.7.8 and 26.6, and Apple has already fixed it in those releases. The advisory compiling the public proof of concept rates the issue high but carries no CVSS score, and it does not name the researcher who published the code.
How the attack works
Two logic flaws inside cupsd, the printing daemon that runs as root, are chained together. An attacker with a normal user account on the Mac first registers a malicious printer, then captures a valid CUPS authentication token while the system probes it. Replaying that token lets them register a second printer configured with a file:// device URI, which aims the "printer" at a local file path instead of at hardware. The path only has to be somewhere that System Integrity Protection, Apple's kernel level guard on system files, does not cover.
Because cupsd validates in the wrong order, it carries out privileged file operations before it has finished its authentication checks. The attacker then submits a print job whose contents they control, and the root level daemon writes that data to the chosen location.
The published script stops short of a root shell. It only demonstrates creating a root owned file and does not automate full privilege escalation, which the researcher was explicit about. That is a real limitation, but arbitrary writes as root are still treated as high impact, because the same primitive can be aimed at configuration files, persistence mechanisms, scheduled tasks or application support files to get the rest of the way. The code reproduces on macOS Tahoe 26.4.1, Sequoia 15.7.5 and Sonoma 14.8.5, with no further user interaction once it runs.
What you should do
Update to macOS 14.8.8, 15.7.8 or 26.6. Apple's own security release notes carry the authoritative version detail. Shared Macs, developer machines, administrative workstations and any endpoint that runs untrusted local software are the ones to do first, because this is a local privilege escalation: an attacker needs a foothold before it is worth anything to them, and those are the systems where a foothold is cheapest.
Where patching lags, the advisory suggests keeping users on standard rather than administrator accounts, restricting who may add or change printer configurations, and watching CUPS for unusual printer registrations, unexpected configuration changes, print destinations that use file:// URIs pointing at sensitive locations, and abnormal print job activity. A public PoC tends to bring opportunistic testing with it, so monitoring matters more now than it did last month.
Local privilege escalation rarely draws the attention a remote bug does, but it is the step that turns a nuisance infection into a full compromise, and macOS has had a busy few months. Apple patched a set of chainable WebKit bugs in June, and criminals have been locking Macs outright to phish the login password.
This briefing is provided by IntelFusions for informational and defensive purposes only. It is based on sources assessed to be reliable at the time of writing, and analytic judgments carry the confidence levels indicated. Indicators of compromise are defanged; re-arm them only in controlled environments. IntelFusions is not affiliated with the organizations named and makes no warranty as to completeness or accuracy.