Описание
In the Linux kernel, the following vulnerability has been resolved:
net/sched: cls_api: Handle TC_ACT_CONSUMED in tcf_qevent_handle
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.
A flaw was found in the Linux kernel's traffic control (TC) classifier application programming interface (API). The tcf_qevent_handle function does not properly handle a consumed socket buffer (skb) when it is processed by the defragmentation engine. This can lead to a Use-After-Free (UAF) vulnerability, where the system attempts to use memory that has already been freed. An attacker could potentially exploit this to cause system instability or execute arbitrary code.
Отчет
This Important flaw in the Linux kernel's networking scheduler can lead to a use-after-free vulnerability. Exploitation requires a local attacker to configure specific tc qdisc and tc filter rules involving RED qdisc with early drop events and connection tracking on fragmented network traffic. This non-default configuration limits the attack surface, but successful exploitation could lead to privilege escalation or a denial of service.
Меры по смягчению последствий
To mitigate this issue, avoid configuring the Linux kernel's traffic control (tc) subsystem with the RED queue discipline (red) that includes qevent early_drop and an action ct filter on interfaces processing fragmented UDP streams. This specific configuration is required to trigger the use-after-free vulnerability.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 6 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel-rt | Not affected | ||
| NVIDIA for RHEL 10 | kernel | Fixed | RHSA-2026:67277 | 14.09.2026 |
| Red Hat Enterprise Linux 10 | kernel | Fixed | RHSA-2026:49211 | 31.07.2026 |
| Red Hat Enterprise Linux 10 | kpatch-patch | Fixed | RHSA-2026:55618 | 17.08.2026 |
| Red Hat Enterprise Linux 10.0 Extended Update Support | kernel | Fixed | RHSA-2026:47620 | 29.07.2026 |
| Red Hat Enterprise Linux 8 | kernel-rt | Fixed | RHSA-2026:49213 | 31.07.2026 |
| Red Hat Enterprise Linux 8 | kernel | Fixed | RHSA-2026:49214 | 31.07.2026 |
| Red Hat Enterprise Linux 8 | kpatch-patch | Fixed | RHSA-2026:55762 | 17.08.2026 |
Показывать по
Дополнительная информация
Статус:
EPSS
7.8 High
CVSS3
Связанные уязвимости
In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_api: Handle TC_ACT_CONSUMED in tcf_qevent_handle 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 fra...
In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_api: Handle TC_ACT_CONSUMED in tcf_qevent_handle 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,
net/sched: cls_api: Handle TC_ACT_CONSUMED in tcf_qevent_handle
In the Linux kernel, the following vulnerability has been resolved: n ...
EPSS
7.8 High
CVSS3