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CVE-2026-98017
net/sched: defer qdisc freeing after failed creation
Published 2026-09-25 (24 days ago) by the Linux kernel CNA. Subsystem include/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-98017 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.7-1 | Update the kernel and reboot. Fixed in 7.2.7-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.7-1 | Update the kernel and reboot. Fixed in 7.2.7-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
An RTM_NEWQDISC request can make clsact bind a populated shared ingress block during ->init(), publishing an embedded mini_Qdisc to lockless readers. If the same request has an invalid TCA_RATE, estimator setup fails after ->init(); the unwind removes the pointer but synchronously frees its containing qdisc while tc_run() may still hold it. Retire failed qdiscs through the same RCU helper as normal destruction. Inline the synchronous free into the callback now that no direct callers remain.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
include/net/sch_generic.h
net/sched/sch_api.c
net/sched/sch_generic.c
- What this is
- NETWORKING [GENERAL]MAINTAINERS section matched on include/net/ · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_NET_SCHED /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sid, bookworm · linux-6.12y
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_NET_SCHED
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-25 (24 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.13%, higher than 2.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- include/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.16 | 6.1.189 | 96a27a3e64e7 |
| 4.16 | 6.6.158 | 6a1b49bb9fdf |
| 4.16 | 6.12.111 | 20bf6fa34b34 |
| 4.16 | 6.18.53 | 156a3bab6974 |
| 4.16 | 7.2.7 | 5bfe927c5b4b |
| 4.16 | 7.3 | e6662f2100f8 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The trigger is a local rtnetlink RTM_NEWQDISC message (tc_modify_qdisc -> qdisc_create) with a clsact kind, a shared TCA_INGRESS_BLOCK and an invalid TCA_RATE. Packets only drive the reader side (tc_run), and no remote peer supplies the input that causes the bug.
- AC:LAttack complexity, low
- The attacker controls both sides of the race: they repeat the failing clsact create, which runs qdisc_free() with no grace period, while pushing traffic through their own veth/dummy device so that tc_run() dereferences the published miniq. No outside condition is needed.
- PR:LPrivileges required, low
- tc_modify_qdisc only needs CAP_NET_ADMIN in the netns that owns the device, which an unprivileged user gets through unshare -Urn plus a self-created veth/dummy interface. That makes it reachable as PR:L rather than requiring init-namespace root.
- UI:NUser interaction, none
- The attacker performs every step themselves: creating the shared block and filter, sending the failing RTM_NEWQDISC, and generating traffic. No victim action is needed.
- S:UScope, unchanged
- The use-after-free and any resulting privilege escalation stay inside the same kernel security authority. No hypervisor or IOMMU boundary is crossed.
- C:HConfidentiality impact, high
- The mini_Qdisc embedded in the freed qdisc (a kmalloc'd object, so its slot can be reclaimed) is read by tc_run: miniq->block and miniq->filter_list are passed to tcf_classify. With a sprayed replacement object, the attacker controls these pointers, which can be used to leak kernel memory.
- I:HIntegrity impact, high
- tc_run calls mini_qdisc_bstats_cpu_update(), which writes through the cpu_bstats pointer taken from the freed object, and tcf_classify follows a filter_list the attacker can control. After reclaim, this gives a controlled write and a path to hijacking control flow.
- A:HAvailability impact, high
- Freeing the qdisc while RCU readers in tc_run still hold its embedded miniq leads to KASAN splats and oopses when the packet path touches the freed or reallocated memory. The result is a kernel crash.