The vulnerability in Incus (github.com/lxc/incus/v7/cmd/incusd) versions prior to 7.2.0 is due to insufficient validation of the backup compression algorithm parameter. The software parses the user-provided compression algorithm string into tokens and only validates the first token against an allowlist of allowed compressors. Additional tokens (arguments) are not validated and are passed directly to the compressor command line. This allows an attacker to inject arbitrary arguments, such as file output redirection, resulting in arbitrary file writes on the host. This can be exploited to write files like cron jobs, leading to arbitrary command execution with the privileges of the Incus daemon. The vulnerability is tracked as CVE-2026-48755 and is rated critical with a CVSS 3.1 vector indicating network attack vector, low attack complexity, low privileges required, no user interaction, scope change, and high impact on confidentiality, integrity, and availability.

An attacker with the ability to trigger backups on an affected Incus instance can exploit this vulnerability to write arbitrary files on the host system. This can lead to arbitrary command execution, such as installing persistent cron jobs, potentially compromising the entire host. The impact includes full system compromise with confidentiality, integrity, and availability severely affected.

A fix is available in Incus version 7.2.0 and later. Users should upgrade to version 7.2.0 or newer to remediate this vulnerability. Until patched, avoid exposing backup functionality to untrusted users or networks. Patch status is confirmed by the affectedVersions field indicating versions prior to 7.2.0 are vulnerable and later versions are fixed.