CVE-2026-74284: Linux Vulnerability

Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_hfsc: Don't make class passive twice update_vf() is called from two places for the same class during a single dequeue when the class's child qdisc (e.g. codel/fq_codel) drops its last packets while dequeuing: 1. The child calls qdisc_tree_reduce_backlog(), which, now that the child is empty, invokes hfsc_qlen_notify() -> update_vf(cl, 0, 0) and turns the class passive (cl_nactive is decremented up the hierarchy). 2. hfsc_dequeue() then calls update_vf(cl, qdisc_pkt_len(skb), cur_time) to charge the dequeued bytes. On the second call the class is already passive, but its child qdisc is still empty, so update_vf() arms go_passive again: if (cl->qdisc->q.qlen == 0 && cl->cl_flags & HFSC_FSC) go_passive = 1; The leaf is then skipped by the cl_nactive == 0 check inside the loop, which does not clear go_passive, so the stale go_passive propagates to the parent and decrements its cl_nactive a second time. A parent that still has other active children is driven to cl_nactive == 0 and removed from the vttree, even though those siblings are still backlogged. They are never dequeued again and the qdisc stalls. Fix this by only arming go_passive when the class is actually active, so an already-passive class no longer triggers a second passive transition. The byte accounting (cl->cl_total += len) still runs for every ancestor, so dequeued bytes continue to be counted exactly once.

Metrics

EPSS Probability

0.21%

11.6th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 72c61ffbeeb8c50f6d4d70c65d3283aa1bac57a7, < a425c82ff06cda5165e0de3de8c2a445ec1f863e; >= a5efc95a33bd4fcb879250852828cc58c7862970, < fc973ecd1a079b9a87c360478542f3a56dea085b; >= 0475c85426b18eccdcb7f9fb58d8f8e9c6c58c87, < 15720cd8fa3fc625146128f89a8e11b0449a20a7; >= 9030a91235ae4845ec71902c3e0cecfc9ed1f2df, < b2a017bfcf565721918ec7355a373911d2f2a227; >= d06476714d2819b550e0cc39222347e2c8941c9d, < 9221a594c72a1446137926d4c2aa04e345f798dc; >= 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb, < 66dbb13eeb2fc339f8f548a9076be4c1a94857b0; >= 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb, < 3a49bbae676fef1ffe548971e6229ae2adeb9d10; >= 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb, < 90b662ea25f5e83bb3b8ccec5b93ced810b92fb8; 9a5fd5c2f4d4afdd5e405083ee53e0789ce76956; c1175c4ad01dbc9c979d099861fa90a754f72059; >= 5.10.241, < 5.10.261; >= 5.15.190, < 5.15.212; >= 6.1.138, < 6.1.178; >= 6.6.90, < 6.6.145; >= 6.12.28, < 6.12.97; >= 5.4.297, < 5.5; >= 6.14.6, < 6.15
Linux	Linux	6.15

References

Timeline

Published: Aug 15, 2026
Last Modified: Aug 17, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-74284?

In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_hfsc: Don't make class passive twice update_vf() is called from two places for the same class during a single dequeue when the class's child qdisc (e.g. codel/fq_codel) drops its last packets while dequeuing: 1. The child calls qdisc_tree_reduce_backlog(), which, now that the child is empty, invokes hfsc_qlen_notify() -> update_vf(cl, 0, 0) and turns the class passive (cl_nactive is decremented up the hierarchy). 2. hfsc_dequeue() then calls update_vf(cl, qdisc_pkt_len(skb), cur_time) to charge the dequeued bytes. On the second call the class is already passive, but its child qdisc is still empty, so update_vf() arms go_passive again: if (cl->qdisc->q.qlen == 0 && cl->cl_flags & HFSC_FSC) go_passive = 1; The leaf is then skipped by the cl_nactive == 0 check inside the loop, which does not clear go_passive, so the stale go_passive propagates to the parent and decrements its cl_nactive a second time. A parent that still has other active children is driven to cl_nactive == 0 and removed from the vttree, even though those siblings are still backlogged. They are never dequeued again and the qdisc stalls. Fix this by only arming go_passive when the class is actually active, so an already-passive class no longer triggers a second passive transition. The byte accounting (cl->cl_total += len) still runs for every ancestor, so dequeued bytes continue to be counted exactly once.

How severe is CVE-2026-74284?

Severity scoring for CVE-2026-74284 is pending analysis. The EPSS model estimates a 0.21% probability of exploitation in the next 30 days.

How do I fix CVE-2026-74284?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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