High 7.8Published Jun 6, 2025

CVE-2025-38001net_sched: hfsc: Address reentrant enqueue adding class to eltree twice

Updated under an hour ago (Oct 28, 2026, 12:10 AM ET)

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Exploited in the last 30 days

In the Linux kernel, the following vulnerability has been resolved: net_sched: hfsc: Address reentrant enqueue adding class to eltree twice Savino says: "We are writing to report that this recent patch (141d34391abbb315d68556b7c67ad97885407547) [1] can be bypassed, and a UAF can still occur when HFSC is utilized with NETEM. The patch only checks the cl->cl_nactive field to determine whether it is the first insertion or not [2], but this field is only incremented by init_vf [3]. By using HFSC_RSC (which uses init_ed) [4], it is possible to bypass the check and insert the class twice in the eltree. Under normal conditions, this would lead to an infinite loop in hfsc_dequeue for the reasons we already explained in this report [5]. However, if TBF is added as root qdisc and it is configured with a very low rate, it can be utilized to prevent packets from being dequeued. This behavior can be exploited to perform subsequent insertions in the HFSC eltree and cause a UAF." To fix both the UAF and the infinite loop, with netem as an hfsc child, check explicitly in hfsc_enqueue whether the class is already in the eltree whenever the HFSC_RSC flag is set. [1] https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=141d34391abbb315d68556b7c67ad97885407547 [2] https://elixir.bootlin.com/linux/v6.15-rc5/source/net/sched/sch_hfsc.c#L1572 [3] https://elixir.bootlin.com/linux/v6.15-rc5/source/net/sched/sch_hfsc.c#L677 [4] https://elixir.bootlin.com/linux/v6.15-rc5/source/net/sched/sch_hfsc.c#L1574 [5] https://lore.kernel.org/netdev/8DuRWwfqjoRDLDmBMlIfbrsZg9Gx50DHJc1ilxsEBNe2D6NMoigR_eIRIG0LOjMc3r10nUUZtArXx4oZBIdUfZQrwjcQhdinnMis_0G7VEk=@willsroot.io/T/#u

CVSS: 7.8 HIGH (v3.1, CNA)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE): Not given
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: Linux
NVD analysis: Modified
Record last updated: Oct 15, 2026
First seen by InfoSec Signals: Oct 15, 2026

Affected products

Affected products

Linux Linux linux:linux (from the name)	from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea before e5bee633cc276410337d54b99f77fbc1ad8801e5; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea before 6672e6c00810056acaac019fe26cdc26fee8a66c; 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea builds before 2c928b3a0b04a431ffcd6c8b7d88a267124a3a28; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea before a0ec22fa20b252edbe070a9de8501eef63c17ef5; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea before 295f7c579b07b5b7cf2dffe485f71cc2f27647cb; 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea builds before 2f2190ce4ca972051cac6a8d7937448f8cb9673c; 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea builds before 4e38eaaabfb7fffbb371a51150203e19eee5d70e; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea before 39ed887b1dd2d6b720f87e86692ac3006cc111c8; and 1 more ranges	CNA record
linux linux_kernel linux:linux_kernel	from 5.0.1 before 5.4.294; from 5.5 before 5.10.238; from 5.11 before 5.15.185; from 5.16 before 6.1.141; from 6.2 before 6.6.93; from 6.7 before 6.12.32; from 6.13 before 6.14.10; from 6.15 before 6.15.1; and 7 more ranges	NVD
debian debian_linux debian:debian_linux	11.0; 12.0	NVD

References

References

https://git.kernel.org/stable/c/e5bee633cc276410337d54b99f77fbc1ad8801e5	patch
https://git.kernel.org/stable/c/6672e6c00810056acaac019fe26cdc26fee8a66c	patch
https://git.kernel.org/stable/c/2c928b3a0b04a431ffcd6c8b7d88a267124a3a28	patch
https://git.kernel.org/stable/c/a0ec22fa20b252edbe070a9de8501eef63c17ef5	patch
https://git.kernel.org/stable/c/295f7c579b07b5b7cf2dffe485f71cc2f27647cb	patch
https://git.kernel.org/stable/c/2f2190ce4ca972051cac6a8d7937448f8cb9673c	patch
https://git.kernel.org/stable/c/4e38eaaabfb7fffbb371a51150203e19eee5d70e	patch
https://git.kernel.org/stable/c/39ed887b1dd2d6b720f87e86692ac3006cc111c8	patch
https://git.kernel.org/stable/c/ac9fe7dd8e730a103ae4481147395cc73492d786	patch
https://syst3mfailure.io/rbtree-family-drama/	third-party-advisory
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The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.