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CVE-2026-72036
net/sched: sch_multiq: Replace direct dequeue call with peek and qdisc_dequeue_peeked
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/sched. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-72036 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 | fixed | 6.1.180-1 | Update the kernel and reboot. Fixed in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
multiq_dequeue() takes a packet from a band's child with a direct ->dequeue() call after multiq_peek() peeked it. When the child is non-work-conserving the peek stashes the skb in the child's gso_skb, so the direct dequeue returns a different skb and orphans the stash, desyncing the child's qlen/backlog. With a qfq child reached through a peeking parent (e.g. tbf) this re-enters the child on an emptied list and dereferences NULL, panicking the kernel from softirq on ordinary egress. Take the packet through qdisc_dequeue_peeked(), as sch_prio already does and as sch_red and sch_sfb were just fixed to do. The helper is a no-op when the child has no stash, so a work-conserving child is unaffected.
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.
net/sched/sch_multiq.c
- What this is
- TC subsystemMAINTAINERS section matched on net/sched/ · netdev@vger.kernel.org · Maintained
- Kernel module
- sch_multiq
Check it on the machine
grep -w CONFIG_NET_SCH_MULTIQ /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.
lsmod | grep -w sch_multiqPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_NET_SCH_MULTIQ
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
- 2026-08-15 (2 months 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
- 0.17%, higher than 5.8% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/sched
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.29 | 5.10.261 | 3e5fd9d14f2d |
| 2.6.29 | 5.15.212 | eb1a9637f0bd |
| 2.6.29 | 6.1.178 | 7a5a15827109 |
| 2.6.29 | 6.6.145 | 86a61e46a191 |
| 2.6.29 | 6.12.97 | 1b9cc255e808 |
| 2.6.29 | 6.18.40 | 5889064919a1 |
| 2.6.29 | 7.1.5 | fffeb2ab5eeb |
| 2.6.29 | 7.2 | 54f6b0c843e2 |
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
- Exploitation requires locally installing a tbf→multiq→qfq hierarchy on a multiqueue netdev via RTM_NEWQDISC/tc netlink before egress can hit multiq_dequeue(); per kernel CNA guidance, tc/qdisc configuration bugs are Local even though the panic fires from softirq during packet transmission.
- AC:LAttack complexity, low
- Once the hierarchy exists, the peek/dequeue mismatch is a deterministic logic bug: tbf peek stashes the QFQ child's skb in gso_skb, then multiq_dequeue's direct child->dequeue() bypasses that stash and re-enters QFQ on an emptied list; ping reproducers for sch_red/sfb show no race or layout dependency.
- PR:LPrivileges required, low
- RTM_NEWQDISC and qdisc grafting are gated by netlink_net_capable(skb, CAP_NET_ADMIN) in rtnetlink_rcv_msg, evaluated against net->user_ns; unprivileged users obtain CAP_NET_ADMIN via user/network namespaces (unshare -Urn) without init-namespace root.
- UI:NUser interaction, none
- No victim interaction is needed after qdisc setup; triggering the NULL dereference requires only attacker-generated egress traffic (e.g., ping) through the defective tbf→multiq→qfq dequeue path.
- S:UScope, unchanged
- The qlen/backlog desync, orphaned gso_skb stash, and resulting kernel panic occur entirely within the host kernel packet scheduler; no VM, IOMMU, or sandbox security boundary is crossed.
- C:HConfidentiality impact, high
- Peek stashes the skb in the non-work-conserving child's gso_skb while direct dequeue returns a different packet, desyncing qlen/backlog—the same scheduler-accounting corruption primitive seen in prior net/sched CVEs and capable of exposing corrupted or freed kernel scheduler memory.
- I:HIntegrity impact, high
- Orphaning the gso_skb stash corrupts parent/child queue linkage and QFQ aggregate scheduling state; inconsistent qlen drives invalid list operations in qfq_dequeue, yielding attacker-influenced memory corruption beyond the demonstrated NULL dereference.
- A:HAvailability impact, high
- The desync re-enters QFQ on an emptied aggregate list and dereferences NULL in qfq_dequeue from softirq during ordinary egress, panicking the kernel as documented in the fix commit and matching KASAN null-ptr-deref traces in the related sch_red/sch_sfb reports.