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CVE-2025-38177 is a flaw in the Linux kernel High-Speed Fair Service Curve (HFSC) traffic-control queueing discipline, sch_hfsc. The hfsc_qlen_notify() routine was not idempotent when invoked through queueing-discipline backlog-reduction paths, including callers such as fq_codel_dequeue(). Repeated invocation could decrement a class's active-count state more than once through update_vf() and attempt repeated removal of the same eligible-tree red-black-tree node. The fix guards update_vf() on a nonzero active count and makes eligible-tree node removal safe by checking and clearing node state.
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No public exploit code observed for this vulnerability.
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18 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A Linux kernel vulnerability in the sch_hfsc component where hfsc_qlen_notify() was not idempotent, leading to an availability impact and resolved by making the function safe for repeated calls.
A Linux kernel HFSC scheduler flaw addressed by making hfsc_qlen_notify() idempotent.
A Linux kernel sch_hfsc flaw concerning non-idempotent hfsc_qlen_notify() behavior. Red Hat addressed it in its RHEL 7.7 AUS kernel update.
A flaw in the Linux kernel sch_hfsc traffic-control scheduler addressed by making hfsc_qlen_notify() idempotent.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.