CVE-2026-87766

A flaw was found in bubblewrap. During sandbox setup, creating files or directories under the new root can follow a parent symlink onto the host via /oldroot, writing attacker-chosen paths outside the sandbox as the launching user. This happens before the sandboxed process starts. This issue is GHSA-pxhw-h44j-8pfx. It is fixed in bubblewrap 0.12.0.

This flaw in bubblewrap is rated as Important because it allows a local attacker to write files outside of a sandbox on the host system. This occurs during the initial setup phase, before any sandboxed process begins, by exploiting symlink traversal when processing untrusted application images, such as those used by Flatpak. While the created files are written with the privileges of the user launching bubblewrap, this can lead to unintended file creation on the host filesystem.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Do not create files on untrusted content with unpatched bwrap. Do not install untrusted Flatpaks. No upstream fix for older setuid builds.