CVE-2025-38177 sch_hfsc: make hfsc_qlen_notify() idempotent
A non-idempotent function in the Linux kernel HFSC scheduler can cause state inconsistencies, potentially leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-38177?
CVE-2025-38177 is a high-severity vulnerability in Debian Debian Linux, published on 4 Jul 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
sch_hfsc: make hfsc_qlen_notify() idempotent
hfsc_qlen_notify() is not idempotent either and not friendly to its callers, like fq_codel_dequeue(). Let's make it idempotent to ease qdisc_tree_reduce_backlog() callers' life:
1. update_vf() decreases cl->cl_nactive, so we can check whether it is non-zero before calling it.
2. eltree_remove() always removes RB node cl->el_node, but we can use RB_EMPTY_NODE() + RB_CLEAR_NODE() to make it safe.
Weakness: CWE-459
Which versions are affected by CVE-2025-38177?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2025-38177?
Apply the vendor's patch.
Is CVE-2025-38177 being exploited?
There is no known exploitation of CVE-2025-38177 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as AZL-72763, BELL-CVE-2025-38177, DEBIAN-CVE-2025-38177, GHSA-9pjq-r2xc-hgwc, ROOT-OS-DEBIAN-11-CVE-2025-38177, ROOT-OS-DEBIAN-12-CVE-2025-38177 and 1 more.