Incus EUVD-2026-16462

The CVSS 4.0 score of 4.7 reflects moderate severity with specific limiting factors: attack vector is local (AV:L), access complexity is low (AC:L), but privilege escalation requires low user privileges (PR:L) and has partial temporal factors (AT:P). The integrity impact is rated high (VI:H) with no confidentiality or availability direct impacts scored in the base vector, though the description acknowledges potential denial of service and privilege escalation on unprotected systems. Exploitation probability (EPSS) is marked as present (E:P), indicating the vulnerability is practically exploitable. Real-world risk is substantially lower than the CVSS score suggests because the attack requires three converging factors: local system access, authenticated user status, and the rare condition of disabled kernel.protected_symlinks (present on only a minority of Linux systems). The vast majority of production systems with default security configurations will encounter Permission Denied errors that block actual exploitation. However, the vulnerability maintains relevance for high-security environments, containerized platforms where users share systems, and non-standard deployments that disable symlink protection. The public availability of an exploit proof-of-concept increases priority for patching in affected environments.

An authenticated user on a system running Incus versions prior to 6.23.0 with kernel.protected_symlinks disabled creates a symlink in /tmp pointing to a critical system file such as /etc/shadow or a service configuration file. When an administrator or another privileged user requests a VM screenshot via the Incus API, the vulnerability causes Incus to write the screenshot through the attacker's pre-positioned symlink, truncating and modifying the target file's permissions. On systems with symlink protection enabled (default), this attack fails harmlessly with Permission Denied, but on unprotected systems, the attacker achieves file corruption, privilege escalation, or denial of service depending on the target file chosen. Public exploit code demonstrating this attack vector exists, reducing the barrier to exploitation for attackers with local access.