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CVE-2026-64530
net/sched: cls_api: Handle TC_ACT_CONSUMED in tcf_qevent_handle
Published 2026-07-26 (3 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-2026-64530 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-4720-1 · 2026-08-05 · text | 6.1.180-1 | Update the kernel and reboot. DLA-4720-1 shipped the fix on 2026-08-05, in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6405-1 · 2026-07-31 · text | 6.12.100-1 | Update the kernel and reboot. DSA-6405-1 shipped the fix on 2026-07-31, 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. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4724-1 · 2026-08-07 · text | 6.12.100-1~deb12u1 | Update the kernel and reboot. DLA-4724-1 shipped the fix on 2026-08-07, in 6.12.100-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
tcf_classify() can return TC_ACT_CONSUMED while the skb is held by the defragmentation engine (e.g. act_ct on out-of-order fragments). When that happens the skb is no longer owned by the caller and must not be touched again. tcf_qevent_handle() did not handle TC_ACT_CONSUMED: it fell through the switch and returned the skb to the caller as if classification had passed. The only qdisc that wires up qevents today is RED, via three call sites (qe_mark on RED_PROB_MARK/HARD_MARK, qe_early_drop on congestion_drop) red_enqueue() was continuing to operate on an skb it no longer owns in this case -- enqueueing it, dropping it, or updating statistics. Resulting in a UAF. tc qdisc add dev eth0 root handle 1: red ... qevent early_drop block 10 tc filter add block 10 ... action ct (with ct defrag enabled and traffic that produces out-of-order fragments, e.g. a fragmented UDP stream) Handle TC_ACT_CONSUMED in tcf_qevent_handle() the same way the ingress and egress fast paths do: treat it as stolen and return NULL without touching the skb. Unlike the TC_ACT_STOLEN case, the skb must not be dropped/freed here, as it is no longer owned by us.
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/cls_api.c
- What this is
- TC subsystemMAINTAINERS section matched on net/sched/ · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_NET_CLS /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_CLS
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
- 2026-07-26 (3 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.54%, higher than 44.0% 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 |
|---|---|---|
| 5.15.148 | 5.15.212 | 5ed3d6f85991 |
| 6.1.75 | 6.1.178 | f42e8134a3a1 |
| 6.6.14 | 6.6.145 | 447d493034a9 |
| 6.8 | 6.12.97 | e1270e69dcf2 |
| 6.8 | 6.18.40 | 2140c2f3f2e7 |
| 6.8 | 7.1.5 | e28aedab9488 |
| 6.8 | 7.2 | a8a02897f2b4 |
| 6.7.2 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4724-1 | 2026-08-07 | bookworm 6.12.100-1~deb12u1 | tracker |
| DLA-4723-1 | 2026-08-07 | bullseye 6.1.180-1~deb11u1 | tracker |
| DLA-4720-1 | 2026-08-05 | bookworm 6.1.180-1 | tracker |
| DSA-6405-1 | 2026-07-31 | trixie 6.12.100-1 | 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:NAttack vector, network
- On a transparent bridge or traffic-shaping gateway configured with the RED qevent and act_ct, unauthenticated remote IP fragments reach red_enqueue() through normal receive, bridge-forwarding, and egress-qdisc processing. No local netlink access is required to trigger the deployed configuration.
- AC:LAttack complexity, low
- The attacker controls fragment contents and ordering and can drive RED into deterministic hard-mark or drop conditions with sustained traffic. No race or condition outside the attacker's control must be won.
- PR:NPrivileges required, none
- CAP_NET_ADMIN is required to create the vulnerable configuration, but a remote attacker sending fragments through an already configured appliance needs no privileges or authentication. Local triggering is also possible with namespaced CAP_NET_ADMIN.
- UI:NUser interaction, none
- Triggering requires only attacker-generated fragmented traffic and does not depend on a victim performing any action.
- S:UScope, unchanged
- The corruption occurs within the host kernel and compromises resources governed by that same security authority. This remains unchanged scope even when used for namespace escape or kernel privilege escalation.
- C:HConfidentiality impact, high
- The reclaimable sk_buff use-after-free and corrupted defragmentation-tree links can be leveraged through attacker-controlled network heap spraying to disclose arbitrary kernel memory.
- I:HIntegrity impact, high
- RED overwrites linkage fields that overlap the defragmentation RB node and may free the object while it remains referenced, enabling subsequent writes through freed or attacker-reclaimed kernel objects and potential code execution.
- A:HAvailability impact, high
- The dangling fragment-tree entry can cause immediate or deferred use-after-free, double-free, invalid tree operations, and kernel panic when another fragment arrives or the queue expires. The attacker can trigger this repeatedly with fragmented traffic.