CVE-2025-21846

In the Linux kernel, the following vulnerability has been resolved:

acct: perform last write from workqueue

In [1] it was reported that the acct(2) system call can be used to trigger NULL deref in cases where it is set to write to a file that triggers an internal lookup. This can e.g., happen when pointing acc(2) to /sys/power/resume. At the point the where the write to this file happens the calling task has already exited and called exit_fs(). A lookup will thus trigger a NULL-deref when accessing current->fs.

Reorganize the code so that the the final write happens from the workqueue but with the caller's credentials. This preserves the (strange) permission model and has almost no regression risk.

This api should stop to exist though.

This vulnerability is rated as Moderate impact because triggering it requires local access with elevated privileges, and the failure mode is restricted to a system crash and denial of service. Under default Red Hat Enterprise Linux configurations, invoking the process accounting interface via the acct system call requires administrative privileges (specifically the CAP_SYS_PACCT capability), which prevents unprivileged local users from exploiting the flaw. Consequently, the issue cannot be triggered remotely or by standard users, limiting the blast radius to environments where untrusted processes already hold elevated permissions.

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.