CVE-2025-37890

A use-after-free vulnerability has been identified in the Linux kernel's HFSC (Hierarchical Fair Service Curve) queuing discipline when it is configured with NETEM (Network Emulation) as a child. This flaw can lead to a kernel panic or crash due to incorrect assumptions about the queue state.

Exploitation of this vulnerability requires local access with CAP_NET_ADMIN privileges and control over the qdisc (queueing discipline) setup. A local attacker could leverage this flaw to achieve denial of service or escalate privileges. Given that it affects kernel memory structures, successful exploitation could result in memory corruption, data leaks, or arbitrary write capabilities, leading to a full kernel crash.

On Red Hat Enterprise Linux 8 and later releases, regular (non-root) users can exploit this issue by abusing unprivileged user namespaces. Red Hat Enterprise Linux 6 and 7 are not affected by this CVE because they did not include the upstream commit that introduced the CVE (37d9cf1).

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.

To mitigate this issue, prevent module sch_hfsc from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically.