CVE-2025-37797
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk8th percentile - higher than 8% of all known CVEs
Summary
In the Linux kernel, a Use-After-Free (UAF) vulnerability was found in the HFSC scheduler's class handling. It results from an incorrect assumption that the queue remains non-empty after calling qdisc_peek_len().
Risk Assessment
An attacker could cause memory corruption or arbitrary code execution by intentionally emptying the queue at the right moment.
Recommendation
Apply the patch that adds a second queue length check after qdisc_peek_len().
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Original NVD description (English source)
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.