Executive brief
The Linux kernel's Landlock security module contains a bypass in its signal delivery controls that allow a sandboxed process to send signals to unsandboxed processes outside its security domain. A malicious application running in a sandbox could exploit this to kill or disrupt critical processes on the system, potentially compromising the security of the entire host and other running applications.
Technical details
The vulnerability is an authorization bypass in Landlock's LANDLOCK_SCOPE_SIGNAL enforcement, which is designed to prevent sandboxed processes from signaling processes outside their security domain. A sandboxed process can set up file or socket owners with specific flags (fcntl F_SETOWN, F_SETSIG, and O_ASYNC) to trigger asynchronous SIGIO signal delivery to a process group containing unsandboxed processes. The kernel's domain recording mechanism in control_current_fowner() fails to properly record the Landlock domain when delivering signals to process groups (PIDTYPE_PGID), only checking if one group member shares the caller's thread group. Additionally, when the process group's thread-group leader has a different domain than the registrant, hook_file_send_sigiotask() incorrectly delegates the decision to a single registration-time check rather than evaluating live domains per recipient. The fix records the registrant's thread group alongside its domain and exempts same-process delivery while blocking out-of-domain group members.
Affected products
- Linux Linux kernel Affected versions through at least 2026-08-15
Timeline
- 2026-08-15: disclosed: Vulnerability published and resolved in kernel
- 2026-08-15: patched: Fix merged addressing the SIGIO path domain recording and thread group exemption