CVE-2026-55480: CUPS copy_model() creates a predictable PPD tempfile without O_EXCL/O_NOFOLLOW (symlink TOCTOU, lp → root)
OpenPrinting CUPS is an open source printing system for Linux and other Unix-like operating systems. Prior to 2.4.20, copymodel() in scheduler/ipp.c creates a predictable TempDir/<connection-number>.ppd path in an lp-group-writable directory and opens it as root without OEXCL or ONOFOLLOW. Exploitation requires an lp-group process able to write that directory to predict the connection-derived name and plant a symlink before the root open, while a privileged add-printer or modify-printer operation using a model PPD triggers copymodel(). The reporter treats an existing lp foothold and the privileged operation as distinct prerequisites, while the maintainer assesses high privileges because installing the relevant filter or administering the printer requires root or print-administrator access. If the race succeeds, the root scheduler follows the symlink and truncates or overwrites a root-writable target with generated PPD data, compromising file integrity or availability. This issue is fixed in version 2.4.20.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
OpenPrinting CUPSto a version that resolves this vulnerability.Fixed in 2.4.20
Event History
Frequently Asked Questions
Who is realistically exposed to this issue?
Systems running OpenPrinting CUPS before 2.4.20 are exposed only where an lp-group process can write the relevant TempDir and a privileged user performs an add-printer or modify-printer operation using a model PPD. The attacker must also win a timing race before the scheduler opens the temporary file as root.
Does exploitation require an existing foothold or administrative access?
Exploitation requires an existing lp-group foothold capable of writing the temporary-file directory. It also requires a privileged printer administration action that triggers copy_model(); the maintainer notes that installing the relevant filter or administering the printer requires root or print-administrator access.
What is the impact if the race is won?
The root scheduler can follow an attacker-planted symlink and truncate or overwrite a root-writable target with generated PPD data. This can compromise the integrity or availability of the targeted file.
What version fixes the issue?
The issue is fixed in OpenPrinting CUPS version 2.4.20.