VulnerabilityPublished 15 Aug 2026Updated 6 Nov 2026

CVE-2026-74284: Linux kernel · net/sched: sch_hfsc: Don't make class passive twice

Affects Linux kernelSource CVE Database V5

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Not known to be exploited · fixed in fc973ecd1a079b9a87c360478542f3a56dea085b : update Linux kernel when convenient.

Data as of 6 Nov 2026, 18:11 UTC

Severity

Medium

Rated Medium by Threat Radar's AI analysis · CVSS not yet scored by NVD

Thin evidence

One scorer or none

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact: Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-11-06.

Patch

Available – fixed in fc973ecd1a079b9a87c360478542f3a56dea085b, b2a017bfcf565721918ec7355a373911d2f2a227, a425c82ff06cda5165e0de3de8c2a445ec1f863e +12

Exploitation evidence

Disclosed: evidence found.
CVE published 15 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 6 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected >=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	Fixed in fc973ecd1a079b9a87c360478542f3a56dea085b b2a017bfcf565721918ec7355a373911d2f2a227 a425c82ff06cda5165e0de3de8c2a445ec1f863e 15720cd8fa3fc625146128f89a8e11b0449a20a7 9221a594c72a1446137926d4c2aa04e345f798dc 90b662ea25f5e83bb3b8ccec5b93ced810b92fb8 66dbb13eeb2fc339f8f548a9076be4c1a94857b0 6.15 6.12.97 6.6.145 6.1.178 5.15.212 5.10.261 5.5 3a49bbae676fef1ffe548971e6229ae2adeb9d10
LinuxLinux	Affected =6.15	Fixed in–

AI-suggested

A fix is available in Linux kernel versions 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97, 6.15, and later. Users should upgrade to these fixed versions to resolve the issue. No additional mitigation steps are required beyond applying the official kernel updates.

Description

A vulnerability in the Linux kernel's HFSC (Hierarchical Fair Service Curve) scheduler caused certain classes to be made passive twice during packet dequeue operations. This double passive transition leads to active classes being incorrectly marked as inactive, causing the queueing discipline (qdisc) to stall and stop dequeuing packets from some active children. The issue has been fixed by ensuring that a class is only made passive if it is currently active, preventing the erroneous second passive transition.

Impact

The vulnerability causes the HFSC queueing discipline in affected Linux kernel versions to stall packet dequeuing for some active classes. This can lead to degraded network performance or traffic disruption on systems using HFSC for traffic shaping. There is no indication of remote code execution or privilege escalation, but network traffic management may be adversely affected until the issue is resolved.

Summary

The Linux kernel's HFSC scheduler had a flaw where the update_vf() function was called twice for the same class during a single dequeue operation when the child qdisc dropped its last packets. The first call correctly made the class passive, but the second call, seeing the class already passive, incorrectly armed the go_passive flag again. This caused the parent's active count (cl_nactive) to be decremented twice, potentially removing a parent class from the virtual time tree even though other children were still active. As a result, those siblings were never dequeued again, causing the qdisc to stall. The fix ensures go_passive is only set if the class is active, preventing the double passive transition while maintaining correct byte accounting.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 6 Nov 2026, 18:11 UTC

Technical details

References

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