CVE-2026-74284
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- CVE-2026-74284
CVE Details
| Release Date: | 2026-08-15 | |
| Impact: | Important | What is this? |
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.
See more information about CVE-2026-74284 from MITRE CVE dictionary and NIST NVD
NOTE: The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 metrics
| Base Score: | 5.5 |
| Vector String: | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
| Version: | 3.1 |
| Attack Vector: | Local |
| Attack Complexity: | Low |
| Privileges Required: | Low |
| User Interaction: | None |
| Scope: | Unchanged |
| Confidentiality Impact: | None |
| Integrity Impact: | None |
| Availability Impact: | High |
Errata information
| Platform | Errata | Release Date |
| Oracle Linux version 10 (kernel-uek) | ELSA-2026-500248 | 2026-09-04 |
| Oracle Linux version 8 (kernel-uek) | ELSA-2026-500249 | 2026-09-04 |
| Oracle Linux version 9 (kernel-uek) | ELSA-2026-500248 | 2026-09-04 |
| Oracle Linux version 9 (kernel-uek) | ELSA-2026-500249 | 2026-09-04 |
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