CVE-2025-37797: Debian Linux

High severity, CVSS 7.8. EPSS: 0.2% chance of exploitation in the next 30 days.

In the Linux kernel, the following vulnerability has been resolved: net_sched: hfsc: Fix a UAF vulnerability in class handling This patch fixes a Use-After-Free vulnerability in the HFSC qdisc class handling. The issue occurs due to a time-of-check/time-of-use condition in hfsc_change_class() when working with certain child qdiscs like netem or codel. The vulnerability works as follows: 1. hfsc_change_class() checks if a class has packets (q.qlen != 0) 2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g., codel, netem) might drop packets and empty the queue 3. The code continues assuming the queue is still non-empty, adding the class to vttree 4. This breaks HFSC scheduler assumptions that only non-empty classes are in vttree 5. Later, when the class is destroyed, this can lead to a Use-After-Free The fix adds a second queue length check after qdisc_peek_len() to verify the queue wasn't emptied.

Affected products

• Debian Debian Linux: version 11.0 only
• Linux Linux Kernel: from 4.14.1, before 5.4.293 (fixed in 5.4.293); from 5.5, before 5.10.237 (fixed in 5.10.237); from 5.11, before 5.15.181 (fixed in 5.15.181); from 5.16, before 6.1.136 (fixed in 6.1.136); from 6.2, before 6.6.89 (fixed in 6.6.89); from 6.7, before 6.12.26 (fixed in 6.12.26); …

Published 2025-05-02. Last modified 2026-07-30.