CVE-2026-115378: Improper Link Resolution Before File Access ('Link Following') in lxc incus

The vulnerability CVE-2026-115378 in lxc's incus component involves improper link resolution before file access in the sftpRecursivePullFile function. This allows a malicious incus-agent running with root privileges inside a virtual machine to escape the target directory during recursive file pulls (incus file pull -r). By returning duplicate entries first as symbolic links and then as files or directories, the attacker can write arbitrary files on the host system, such as /etc/shadow, potentially compromising host security. The affected versions are all incus versions prior to 6.0.7, versions from 6.1.0 up to but excluding 7.0.2, and versions from 7.1.0 up to but excluding 7.5.0. The CVSS 4.0 vector indicates network attack vector, low attack complexity, partial attack traceability, and high impact on integrity and system availability.

An attacker with root privileges inside a virtual machine can exploit this vulnerability to write arbitrary files on the host system by escaping the intended directory during file pull operations. This can lead to overwriting critical host files such as /etc/shadow, potentially allowing privilege escalation or host compromise. The impact affects host integrity and availability but does not affect confidentiality according to the CVSS vector.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. No official patch or fix links are provided in the available data. Until a fix is confirmed, restrict root access within virtual machines and avoid using incus file pull operations with untrusted agents. Monitor vendor communications for updates on patches or official mitigations.